Horticultural Reviews, Volume 21

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HORTICULTURAL REVIEWS Volume 21

Horticultural Reviews is sponsored by: American Society for Horticultural Science

Editorial Board, Volullle 21 Louise Ferguson R.E.C. Layne Ian J. Warrington

HORTICULTURAL REVIEWS Volume 21

edited by

Jules Janick Purdue University

John Wiley 8' Sons, Inc. NEW YORK / CHICHESTER / WEINHEIM / BRISBANE / SINGAPORE / TORONTO

This text is printed on acid-free paper. Copyright © 1997 by John Wiley & Sons, Inc. All rights reserved. Published simultaneously in Canada. Reproduction or translation of any part of this work beyond that permitted by Section 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful. Requests for permission or further information should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY 10158-0012.

This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If legal advice or other expert assistance is required, the services of a competent professional person should be sought. Library of Congress Catalog Card Number: 79-642829 ISBN 0-471-18907-3 ISSN 0163-7851 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

Contents List of Contributors

ix

Dedication

xi

1. Integrated Management of Greenhouse

Vegetable Crops

1

A. P. Papadopoulos, S. Pararajasingham, f. 1. Shipp, W. R. Jarvis, T. f. Jewett, and N. D. Clarke I. II. III. IV. V.

Introduction Greenhouse Climate Responses of Cucumber, Pepper, and Tomato Integrated Management of the Crop Future Prospects Literature Cited

2. Okra: Botany and Horticulture Eftal Diizyaman

I. II. III. IV.

Introduction Botany Horticulture Research Needs Literature Cited

3. Sweet Sorghum

2

4 7

18 28 30

41 42

43 55 62 63

73

E. 1. Hunter and 1. C. Anderson I. II. III. IV.

Introduction Botany Crop Physiology Genetic Improvement

73 74 84

87 v

CONTENTS

vi

V. VI.

Syrup Production Future Prospects Literature Cited

4. Deficit Irrigation in Deciduous Orchards

91 99 100

105

M. H. Behboudian and T. M. Mills

I. II. III. IV. V.

Introduction The Concept of Deficit Irrigation Physiology of Deficit Irrigation Establishment of Irrigation Schedules for Deficit Irrigation Future Prospects Literature Cited

5. Germplasm Resources of Pineapple Ceo Coppens d'Eeckenbrugge, Freddy Leal, and Marie-France Duval

I. II. III. IV. V.

Intro duction Genetic Base and Genetic Diversity Problems of Genetic Significance Germplasm Maintenance and Utilization Future Prospects Literature Cited

6. Salinity Tolerance in Olive R. Cucci and M. Tattini I. II. III. IV. V. VI. VII. VIII.

Introduction Units Expressing Salinity Effects of Salinity on Olive Performance Physiological Mechanisms Cultural Implications Factors Affecting Salinity Tolerance Interactions with Other Abiotic Stresses Conclusions Literature Cited

106 107 113 122 126 127

133

134 142 154 164 168 169

177

178 179 180 185 198 204 205 206 207

CONTENTS

vii

7. Cranberry: Botany and Horticulture

215

Teryl R. Roper and Nicholi Vorsa I. II. III. IV. V.

Introduction Botany Horticulture Environmental Issues Future Prospects Literature Cited

216 223 229 239 242 243

Subject Index Cumulative Subject Index Cumulative Contributor Index

251 253 275

Contributors I. C. Anderson, Department of Agronomy, Iowa State University, Ames, Iowa 50011 M. H. Behboudian, Department of Plant Science, Massey University, Palmerston North, New Zealand N. D. Clarke, AI Solutions, 47 Tomlin Crescent, Richmond Hill, Ontario, Canada L4C 7T1 Geo. Coppens d'Eeckenbrugge, CIRAD-FLHOR/IPGRI, c/o CIAT, AA 6713, Cali, Colombia Marie-France Duval, CIRAD-FLHOR, B.P. 153, Fort-de-France, Martinique, FWI Eftal Diizyaman, Department of Horticulture, University of Ege, Izmir, Turkey 35100 R. Gucci, Dipartimento di Coltivazione e Difesa delle Specie Legnose, Sezione Coltivazioni Arboree, Universita di Pisa, Via del Borghetto 80, Pisa, Italy 56124 E. L. Hunter, Department of Agronomy, Iowa State University, Ames, Iowa 50011 Jules Janick, 1165 Horticulture Building, Purdue University, West Lafayette, IN 47907 W. R. Jarvis, Greenhouse and Processing Crops Research Center, Agriculture & Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO T. J. Jewett, Greenhouse and Processing Crops Research Center, Agriculture & Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO Freddy Leal, UCV Facultad de Agronomia, Apartado 4736, Maracay, Aragua, Venezuela Paul Lyrene, University of Florida T. M. Mills, Environment Group, HortResearch, Palmerston North, New Zealand A. P. Papadopolous, Greenhouse and Processing Crops Research Center, Agriculture & Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO S. Pararajasingham, Greenhouse and Processing Crops Research Center, Agriculture & Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO Teryl R. Roper, Department of Horticulture, University of Wisconsin-Madison, Madison, Wisconsin 53706 J. L. Shipp, Greenhouse and Processing Crops Research Center, Agriculture & Agri-Food Canada, Harrow, Ontario, Canada NOR 1GO M. Tattini, Istituto sUlla Propagazione delle Specie Legnose, Consiglio Nazionale delle Richerche, Scandicci, Firenze, Italy 50018 Nicholi Vorsa, Blueberry and Cranberry Research Station, Rutgers University, Chatsworth, New Jersey 08019 ix

Wayne B. Sherman

Dedication: Wayne B. Sherman This volume is dedicated to Wayne B. Sherman, a leading world authority on breeding low-chill fruit cultivars. Although principally known for his work with peaches and nectarines, Wayne is also a breeder of blueberries, citrus, strawberries, plums, pears, apples, blackberries, persimmons, cherries, apricots, dogwood, and Rhododendron species native to the southeastern United States, and he has released cultivars of many of these species. Wayne was born in Lena, Mississippi, in 1940 and grew up on a small farm near the Pearl River in central Mississippi. During his childhood and youth, he was an avid hunter and fisherman, and his rambles through the forests and swamps made him a close observer of nature. Wayne remains a superb naturalist, with a wide-ranging knowledge of the plants and animals, geology, and weather of the southeastern United States. He is an avid bow hunter and, with the possible exception of his wife Etoyle, is probably more successful at fishing than any other person in Alachua County. Wayne received his B.S. degree in Horticulture and his M.S. in Pomology, both from Mississippi State University, and he received his Ph.D. in plant genetics and breeding from Purdue University in 1966. Except for a sabbatical in eastern Australia, Wayne has spent his entire career as a fruit breeder in the Horticultural Sciences Department at the University of Florida in Gainesville. Wayne's success as a plant breeder is due to an outstanding combination of personal talents and work habits. One special skill is his almost incredible ability to accurately determine the value of a seedling from slight evidence. In his first-stage selection nursery, where seedlings grow at densities 300 times greater than in commercial plantings, Wayne selects or eliminates seedlings the first year they fruit, sometimes on the basis of a single fruit. This high-density "fruiting nursery" system, which Wayne did much to develop, allows him to screen thousands of seedlings in a small area at minimal cost. Skeptics might claim that much of the variation Wayne sees among the trees in the high-density nursery is not genetic and would not persist in an orchard, but the steady stream of superb cultivars that emerges from his breeding proxi

xii

DEDICATION

gram proves the effectiveness of his methods and his uncanny abilities. Wayne Sherman's peach trees are not only planted by the hundreds of thousands in the United States but have also achieved great success worldwide, from Mexico to Egypt, from Argentina to Australia. Luther Burbank once claimed that he could walk down a row of seedlings that looked uniform to other observers and pick out superior plants as fast as an assistant could tie on the marker ribbons. This claim sounds exaggerated, but Wayne does the same thing in his peach-breeding nurseries. Because of his skill and long experience with peaches, and because he is so alert and focused on what he is looking for, Wayne is able to see things that most would neither notice or consider important. Few are born with an artist's eye or a musician's ear; fewer still are born with Wayne's tremendous ability to select plants. Wayne's great success as a plant breeder rests heavily on his Burbank-like ability to recognize good plants amid a jungle of stems and leaves. A similar intuition allows Wayne to plan successful crosses based on his knowledge of parental clones. Breeders with less intuition have spent decades in unsuccessful toil because the parents they chose lacked the necessary combining ability to give rise to extraordinary genotypes such as a 'Sharpblue' blueberry or a 'Floridagold' peach. Other factors contribute to Wayne's success. He works extremely fast. He can bud a row of peaches before most people can find their budding knife. He has a great ability to identify solvable problems whose solutions would have large and beneficial consequences. His total confidence in the power of plant breeding to achieve quick and dramatic results is exemplified by two typical Wayne Shermanesque statements: "If we could breed a truly cold-hardy citrus variety with delicious fruit, every homeowner from Houston, Texas to Savannah, Georgia, would plant a tree in their back yard, and I know what cross to make to get it." "Using the nonmelting flesh gene, we can breed a high-quality peach for the fresh market that can be harvested tree-ripe and still shipped long distances; when millions of consumers discover the flavor of a tree-ripe peach, there will be a revolution in the fresh peach industry." Wayne not only has great vision, but he also has the confidence, the skill, and the energy to turn his visions into reality. Wayne's contributions to the science of horticulture go far beyond his breeding program. For example, he offers the most practical advice on chill hours: "The chilling situation on your farm can be deduced from the mean temperature of the coldest month of the year; thus, choose varieties from those that have done well in other parts of the world where the mean temperature of the coldest month is the same as at your farm." He has published countless articles on breeding methods, on the results

DEDICATION

xiii

of breeding with various unique germplasms, and on the biology of disease and insect pests he has studied in his breeding plots. He has trained numerous graduate students, served as graduate coordinator for the Horticultural Sciences Department, has given advice to hundreds of growers, has instructed and entertained a stream of visitors from all parts of the world, and has taught courses in pomology, plant breeding, and plant propagation for both graduate and undergraduate students. He inspires, motivates, and energizes both students and colleagues. He has received many awards and honors internationally, nationally, and locally. To exemplify, he was elected a Fellow of the American Society for Horticultural Science; he was awarded the Wilder Medal of the American Pomological Society; and he received the best research paper of the year award from the Florida State Horticultural Society. Wayne is not only a first-class scientist, but is also a loyal and generous friend to the many who have passed his way. A conversation with Wayne is a fascinating experience. His stories, insights, knowledge, and opinions are truly memorable. Wayne is an extraordinary horticulturist, and as a breeder, he emulates one of his personal heroes, Luther Burbank. Wayne Sherman has contributed a great deal to our world, and we are privileged to know and honor him. Paul Lyrene University of Florida Jules Janick Purdue University

1 Integrated Management of Greenhouse Vegetable Crops A. P. Papadopoulos, S. Pararajasingham, f. 1. Shipp, W. R. Jarvis, and T. f. Jewett Greenhouse and Processing Crops Research Center Agriculture and Agri-Food Canada Harrow, Ontario Canada NOR lGO N. D. Clarke AI Solutions 47 Tomlin Crescent Richmond Hill Ontario, Canada L4C 7Tl

1. Introduction II. Greenhouse Climate III. Responses of Cucumber, Pepper, and Tomato A. Aerial Environment 1. Radiation 2. Temperature 3. Humidity 4. Carbon Dioxide B. Root Environment IV. Integrated Management of the Crop A. Environmental Management B. Pest and Disease Management 1. Pest 2. Disease V. Future Prospects Literature Cited

Horticultural Reviews, Volume 21, Edited by Jules Janick ISBN 0-471-18907-3 © 1997 John Wiley & Sons, Inc. 1

2

A. P. PAPADOPOULOS et al.

I. INTRODUCTION In many countries where climate prevents or reduces the choices for year-round outdoor crop production, vegetable production also takes place in protected environments (Hanan et al. 1978; Wittwer and Castilla 1995). With greenhouses being the most efficient means to overcome climatic adversity (Hanan et al. 1978; Wittwer and Castilla 1995), greenhouse vegetable production makes use of recent advances in technology to control the greenhouse environment for maximizing crop productivity per unit area (Manrique 1993). The world greenhouse area as a whole is only a minuscule part of that devoted to worldwide agricultural operations but, in some cases, the income can be a significant factor in improving a country's farm income and foreign exchange earnings from exports. The global greenhouse (plastic plus glass houses) industry consisted of only 279,000 ha (Wittwer and Castilla 1995) compared to the total area under wheat cultivation in the world in 1989 which was estimated to be 225 million ha (Verreet 1995). In 1992, the value of Dutch greenhouse vegetables was u.s. $1.6 billion (Ammerlaan 1994), while in Canada it was U.S. $98 million (Statistics Canada 1993). An estimate of the U.S. greenhouse vegetable industry revealed that, in 1988, greenhouse vegetables were grown on 120 ha with total sales reaching U.S. $31.7 million (Snyder 1993). Most countries with a sizeable greenhouse vegetable industry (Table 2 in Wittwer and Castilla 1995) span latitudes between 26°N (Florida, USA) and 65°N (Finland). Within these latitudes, the local climate can vary from extremely hot (> 40°C) and humid in the summer to extremely cold « -40°C) and dry in the winter. Growers in these countries are faced with the need to control the greenhouse environment to maximize crop production with the minimum expenditure of energy and other inputs to remain competitive in increasingly open international markets. A description of the engineering aspects of greenhouse structures for energy conservation can be found in White (1979). Recent developments in the greenhouse vegetable industry worldwide have highlighted the need to improve the level of environmental control available to the growers. The widespread use of airtight plastic structures in most countries (Wittwer 1993) has resulted in humidity problems within the greenhouses (White 1979). The use ofCO z enrichment is now commonplace. Computer-controlled fertigation systems (Papadopoulos and Liburdi, 1989) are becoming popular among European and North American greenhouse vegetable growers. The supply of nutrients and the use of chemicals for pest and disease control are

1. INTEGRATED MANAGEMENT OF GREENHOUSE VEGETABLE CROPS

3

on the decline because of public demand for safer food products and more stringent environmental regulations (Clarke et al. 1994). Biological control methods are prevalent as alternatives to chemical control of pests and diseases (Shipp et al. 1991). As a result, growers are looking for means that will enable them to control both the aerial and root environments of the greenhouse with more precision to increase crop productivity, to decrease pest and disease incidence, and to promote the activity of biological control agents (Clarke et al. 1994). Most European and North American greenhouse vegetable enterprises have now installed computer-controlled environmental systems that offer the potential to control the greenhouse environment in ways that were not possible in the past (Shipp et al. 1991). The use of computers permits the control of greenhouse equipment by one or more of several factors (Bailey 1995). For example, inside temperature, CO 2 , and humidity can now influence the operation of vents. The grower is still responsible for choosing the array of set points and keying them into the computer. When a grower selects a set point for an environmental factor in the greenhouse, it represents the grower's perceptions of current crop condition, outside weather, triggers for pest and disease outbreaks, and market trends. Greenhouse environmental control decisions, in practice, are more intuitive than analytical (Jones et al. 1988; Clarke et al. 1994). Thus, a critical need exists for the development of tools that will complement growers' knowledge with additional information on (a) the physical, chemical, and biological factors that create the greenhouse environment and their interaction; (b) growth of crops; (c) how crop growth is modified by the greenhouse and vice versa; and (d) pest-and disease-control strategies. Current computer-controlled greenhouse environmental systems merge knowledge and information in greenhouse management in order to increase crop productivity while slowing development of pests and diseases. Greenhouse crop management that uses information from many diverse sources is called integrated crop management. The management of the greenhouse environment to which the aerial portion of the plant is exposed has been discussed in detail more recently by Bailey (1995), Bakker (1995), and Bakker et al. (1995). The purpose of this review is twofold: (1) to provide an overview of how greenhouse crops respond to factors that constitute the greenhouse environment, and (2) to introduce integrated crop management programs to the greenhouse vegetable industry. Tomato, cucumber, and pepper were chosen as model crop examples because of their worldwide economic significance (Wittwer and Castilla 1995).

4


II. GREENHOUSE CLIMATE The greenhouse environment can be looked at as two distinct parts (Rudd-Jones 1978): the aerial environment and the root environment. The physical factors-light, temperature, humidity, wind speed, and CO 2 concentration-that need to be controlled in the aerial environment are often referred to as greenhouse climate (e.g., Bot 1983). The term greenhouse climate usually denotes the spatial average climate inside a greenhouse as opposed to the microclimate in a particular area, the assumption being that the greenhouse behaves as a perfectly stirred tank with a uniform spatial distribution of climate variables (Udink ten Cate 1983). Greenhouse temperature usually refers to the spatial average temperature of the air in the greenhouse. Temperature is measured at a central location with a sensor shielded from the sun and aspirated at air speeds of 2 to 4 m S-1 (Gieling and Schurer 1994). The relative humidity of greenhouse air is measured in conjunction with air temperature so that the vapor pressure deficit (VPD) of greenhouse air may be calculated. Vapor pressure deficit, the difference between the saturation vapor pressure of air and the ambient vapor pressure for a given temperature, air moisture content, and atmospheric pressure, is the most appropriate variable for greenhouse humidity management because it is directly related to crop transpiration. Carbon dioxide concentration in greenhouses refers to the spatial average concentration of CO 2 CuI L-1 ) in the air. The speed and direction of air movement in a greenhouse vary greatly, and are assumed to be variable enough to cause complete air mixing. Depending on the context, different measures of light level are used for greenhouse climate studies (Cathey and Campbell 1980; Nobel 1991). When discussing the energy balance of a greenhouse, the flux of radiant energy received from the sun on a horizontal surface outside the greenhouse is the quantity used. The radiometric flux of solar energy is called solar irradiance and is measured in W m- 2 • Radiometers typically used for solar irradiance measurements for greenhouse climate control are responsive to shortwave radiation. When discussing photosynthesis, the photon flux in the wavelength band of 400 to 700 nm (photosynthetically active radiation, PAR) on a horizontal surface, the photosynthetic photon flux density (PPFD) in .umol m-2 S-1, is used. Radiation in the wavelength range of 0.15 to 3 .urn is designated as shortwave radiation, whereas that in the range of 3 to 100.um is designated as longwave, infrared, or thermal radiation (Oke 1978). The spectral distribution of solar radiation below the earth's atmosphere is such that 95 % of the solar energy received is in the 0.4 to 2.8.um wavelength band (Coulson 1975).


5

Local weather patterns have a major effect on the climate inside greenhouses. Areas with a maritime climate tend to have more cloud cover and less PPFD at ground level than those with a continental climate (Short and Bauerle 1989). Reduced PPFD is a disadvantage in winter but a significant advantage in summer when high irradiance levels cause greenhouse air temperature to be too high. Areas with maritime climates also tend to have less variability in day-to-day PPFD. Rapid fluctuations in PPFD perturb crops if they are not acclimatized to high radiation levels. Extreme outdoor air temperatures and VPDs in some locations make it difficult or impossible to control greenhouse climate within acceptable limits at certain times of the year. At very low outside air temperatures, air has a low moisture-holding capacity. When cold air infiltrates into greenhouses and is warmed to the greenhouse air temperature, the VPD of the greenhouse air can become too high if systems for humidification are not used. At very high outside temperatures and VPDs, ventilation and infiltration air entering greenhouses has an extreme drying effect. Under these conditions, humidification of the greenhouse air can decrease VPD and temperature (through the process of evaporative cooling) to acceptable levels. At very high outdoor air temperatures and low VPDs, air has very little evaporative cooling potential. In consequence, greenhouses in hot and humid climates cannot be cooled effectively. Local wind patterns also affect greenhouse climate. In winter, high wind speeds increase the surface heat transfer coefficients, resulting in greater heat loss. High wind speeds also increase heat and moisture loss in winter by increasing air infiltration. In summer, air speed has a major effect on ventilation effectiveness. Moderate wind speeds create the turbulence and pressure differentials necessary for good air movement into and out of greenhouses through vents. In addition to providing a physical barrier between the inside and the outside, greenhouse structures also affect the greenhouse climate. The structural component that has the greatest effect is the greenhouse cover. Despite modern designs and construction, greenhouses seldom transmit more than 70% of the available solar irradiance (Cockshull 1992; Stanghellini 1994) because of reflection and absorption of the cover and shading from structural members. Greenhouse covers have the property of transmitting most of the incoming shortwave radiation but are partly or completely opaque to outward thermal radiation (Bot and Challa 1991). This entrapment of longwave radiation, known as the greenhouse effect, can raise the temperature inside a greenhouse 22%

6


according to an estimate by Bot (1983). Glass is opaque to reradiation in the thermal wavelength region of 5 to 50 flm (Bot 1993). Most plastic cover materials are partly transparent to longwave radiation but when water vapor condenses at the inner surface (see Section IV) these covers act, for the most part, as net energy absorbers. The temperature at which the cover materials emit and absorb radiation is important for radiation exchange between the greenhouse and the outside environment (Bot and Challa 1991). Other structural components that affect the greenhouse climate include glazing bars, gutters and columns, the floor material, and the greenhouse vents. All internal surfaces of the greenhouse that are cooler than the dewpoint temperature of the greenhouse air condense moisture from the air. The design of glazing bars and their general state of repair affect the air infiltration rate which in turn affects the rate of heat, moisture, and CO 2 exchanges with the outside. The covering on the floor either reflects or absorbs solar radiation and can have a significant effect on the lighting environment and the thermodynamics of the greenhouse. White polyethylene mulch is often used on the greenhouse floor to maximize light reflection and to minimize heat absorption by the floor. With the vents closed, there is a large local reduction in wind speed inside a greenhouse. Circulation fans are often used to create air movement under these conditions. When the vents are opened, internal wind speeds, as well as the heat, moisture, and CO 2 exchange with the outside increase dramatically. The crop itself influences greenhouse climate. The primary reason for this is that greenhouse crops are effective absorbers of solar radiation. Most of the solar energy absorbed by crops is transferred to the greenhouse air as latent heat through the process of evapotranspiration. Less than 1 % of the light available is actually used by greenhouse crops in the production of biomass (Warren Wilson 1972). In experiments with greenhouse tomato, Stanghellini (1987) measured transpiration rates in the range of 150 to 200 W m-2 at irradiance, temperature, CO 2 , and VPD levels of 500 W m-2 , 25°C, 800 fll L-1, and 0.2 to 0.9 kPa, respectively. Crops also affect the climate inside greenhouses by consuming CO 2 , With vents closed, actively photosynthesizing crops can deplete CO 2 to levels well below ambient levels found outside. Nederhoff (1994) measured CO 2 uptake of a tomato crop in the range of 3 to 5 g m-2 h-1 in a greenhouse enriched to 1000 fll L-1 CO 2 , Greenhouse crop canopies attenuate the radiation reaching the greenhouse floor; in so doing, they affect the thermodynamics of the greenhouse even though the thermal mass of the crop is small. Greenhouse crop canopies also provide significant resistance to air movement.


7

The net result of the interaction between outside weather, greenhouse structure, and the crop results in a climate that is generally warm, humid, wind free, and COz-depleted inside the greenhouses (Jarvis 1992). Without a climate-control system, the climate for crop processes is worse inside a greenhouse than it is outside during the summertime (Stanghellini 1994) but ideal for pests and pathogens. Climate-control equipment is used to create a greenhouse climate close to the optimum required for crop processes.

III. RESPONSES OF CUCUMBER, PEPPER, AND TOMATO

A. Aerial Environment 1. Radiation. The relation between PPFD and photosynthesis of individual leaves is well documented (Papadopoulos and Pararajasingham 1997). Usually, radiation use efficiency is high in a crop canopy because radiation is distributed over leaves with different orientations and positions within the canopy. Only a small fraction of the leaves will receive full sunlight (Bot and Challa 1991). Simulation studies have shown that in closed canopies of greenhouse tomato, photosynthesis does not show saturation up to a PPFD of 2000 tlmol m- z S-1 (or 1000 W m- z global radiation) (Gijzen 1995). Crop growth rate is linearly related to crop photosynthesis (Penning de Vries and van Laar 1982) as,

[Eq.l]

where Y = crop growth rate (g m-z d-1); a conversion efficiency (g biomass g-1 CHzO); P = gross photosynthesis (g CHzO m-z d-1); and Rm = maintenance respiration (g CHzO m- z d-1). Ehler and Karlsen (1993) used a value of 0.68 as the conversion factor for g CO z to g glucose, and 0.7 as the ratio of structural biomass formed per amount of glucose consumed. The lower PPFD found inside greenhouses compared to the ambient, with corresponding decreases in P, is a constraint for crop production in greenhouses. According to Eq. 1, to increase biomass production, P must be increased or maintenance respiration reduced. Integrated crop management, in essence, is an endeavor to ensure that total biomass production remains high by manipulating the environmental factors to increase P or reduce Rm . In young plants, the interception of PPFD is given by:

IlIa = 1 - e-kLA1

[Eq.2]

8


where 1 = PPFD absorbed by the crop; 10 = PPFD at the top of the canopy; k = extinction coefficient of the canopy; LAI = leaf area index (leaf area per unit land area). Acock et al. (1978) reported a value of k = 0.63 for the upper leaf layer and stem in a tomato canopy; the k value decreased to 0.52 with depth in the canopy. In sweet pepper, kwas found to be 0.42 for overcast skies and 0.2 to 0.3 around noon under clear skies (Hand et al. 1993). Greenhouse crops of tomato, cucumber, and pepper are normally grown in rows or double rows oriented N-S and have a mature height of 2 m or more. The row canopy with intervening paths and gaps has profound effects on the interception ofPPFD (Hand et al. 1993). These effects have been examined in greenhouse crops by means of various models, a review of which for greenhouse tomato can be found in Papadopoulos and Pararajasingham (1997). Light interception in greenhouse row crops has been examined by Nederhoff (1984) for cucumber, Papadopoulos and Ormrod (1988) for tomato, and Hand et al. (1993) for sweet pepper. For cucumber, Nederhoff (1984) reported that PPFD interception was dependent on the LAI rather than on plant density. In tomato, Papadopoulos and Ormrod (1988) found that the proportion of available PPFD intercepted increased as plant spacings became closer, but at wide plant spacings PPFD penetration into the canopy increased. Light interception measurements by Hand et al. (1993) in sweet pepper revealed that at row intervals of 1.6 m, a N-S-oriented row canopy achieves a PPFD interception exceeding 90% under overcast skies and 94% for much of the day under clear skies. However, around noon for the crop as a whole, the interception falls to about 80% for about an hour, lowering photosynthetic productivity, especially when CO 2 enrichment is used. Early growth of crops is exponential because at low LAI, PPFD interception, P, and Yare linearly related to LAI (Challa et al. 1995). Leaf area ratio (LAR), the ratio between leaf area and total crop biomass, has been shown to increase with declining light intensity, thus partly compensating for the loss in photosynthesis per unit leaf area per unit time (net assimilation rate, NAR) (Bruggink and Heuvelink 1987). As a result, in tomato, cucumber and sweet pepper seedlings, relative growth rate (RGR = LAR x NAR) is not proportional to variations in light integrals (Bruggink 1987). In crops with closed canopies, PPFD interception can be enhanced by better greenhouse structures (Critten 1993), optimum plant populations (Papadopoulos and Pararajasingham 1997) and the use of genotypes better adapted to low-light environments (Papadopoulos and Ormrod 1988;1990). At present, supplementary artificial lighting in greenhouse


9

vegetable production usually costs too much to be commercially worthwhile. Leaf area is a major determinant of crop growth rate (Watson 1952). Leaf number, the main component of total leaf area, is a function of leaf appearance rate. Temperature is a major limitation to leaf appearance rate in crops (Kiniry et al. 1991). An influence of light intensity on leaf appearance rate in cucumber has been reported by Marcelis (1993). In sweet pepper and tomato, Heuvelink and Marcelis (1996) examined the effect of altering the assimilate supply on leaf appearance rate by varying PPFD, plant density, and leaf, truss, and fruit thinning. In sweet pepper, as PPFD was increased from 20 to 80 W m- 2 , leaf appearance rate varied from 0.204 to 0.222 leaves day-1 (p > 0.05). As the percentage of leaves removed below the fourth node of the main branch was increased from 0 to 80%, vegetative biomass decreased from 50.5 to 34.2 g plan-t-1 while number of leaves visible at the end of experiment was 12.1 and 12.4 plant -1, respectively (p > 0.05). In tomato, increasing the plant density from 1.6 to 3.1 plants m-2 and fruit number from 1 to 7 fruits per truss reduced vegetative biomass by 45 and 40%, respectively, whereas visible leaf number plant-1 was unaffected. In tomato, increasing the assimilate supply resulted in an increase in leaf biomass and area per leaf and a decrease in specific leaf area (SLA = m 2 leaf area g-l leaf biomass). For sweet pepper grown under daylight conditions at a constant 24-h temperature, the rate of biomass increase of total plant and vegetative parts changed considerably (coefficient of variation (CV) 0.52 and 0.44, respectively) but leaf appearance rate remained constant during the growing season (CV = 0.07). A faster leaf appearance rate at higher PPFD levels was evident in sweet pepper seedlings. Several authors (e.g., Calvert 1959; Hussey 1963; Klapwijk 1981) have reported a reduction in leaf appearance rate with a decrease in PPFD levels during the early development of tomato. Heuvelink and Marcelis (1996) concluded that assimilate supply had little effect on leaf appearance rate during the production stage of sweet pepper and tomato. 2. Temperature. In the relationship between gross photosynthesis and biomass production (Eq. 1), temperature affects the rates of gross photosynthesis and maintenance respiration, although conversion efficiency is unaffected by temperature (Bot and Challa 1991). The optimal leaf temperature for photosynthesis ranges between 20 and 35°C (Fitter and Hay 1981). In closed canopies, under the conditions normally found in greenhouses, the effect of temperature on simulated crop photosynthesis was less than that observed for individual leaves (Gijzen 1995). However, under the conditions of high PPFD and high

10


COzlevels, temperature influences crop photosynthesis significantly by raising the photosynthetic capacity to potential levels (Gijzen 1995). Leaf area is a major determinant of crop growth rate, and temperature is the main determinant of leaf area development. Several studies [e.g., Nilwik (1981)-sweet pepper; Challa & Brouwer (1985)-cucumber; Smeets and Garretsen (1986); and Heuvelink (1989)-tomato] have demonstrated that the changes in RGR during the seedling stage in response to temperature is mainly caused by changes in LAR and not by changes in NAR. Gaastra (1959) found that at 300 ,ul L-1 CO z, temperatures in the range of 12.5 to 20.5°C had minimal effect on the net photosynthesis of tomato leaves. In contrast, Friend and Helson (1976), working with wheat, suggested that the high growth rate obtained under a temperature regime of high day temperature was the result of a high rate of net photosynthesis. In cucumber, a decline in NAR below a day temperature of 18°C (Kleinendorst and Veen 1983) and a night temperature of 12°C (Challa and Brouwer 1985) has been reported. In sweet pepper, at a daily irradiance integral of 3.25 MJ m-z, NAR decreased when temperature was decreased from 25 to 21°C, suggesting that at high irradiance levels, a temperature of 21°C is suboptimal for net photosynthesis in this crop (Nilwik 1981). Among the components of LAR (SLA x LWR), the data of Heuvelink (1989) indicated that although LWR (g leaf biomass g-1 crop biomass) was independent of temperature, SLA was sensitive to temperature changes. Nilwik (1981) reported a high correlation between LAR and specific leaf weight (l/SLA) for sweet pepper. Warren Wilson (1966) reported for field crops that temperature affects growth mainly through its effect on LAR (not NAR) and SLA (not LWR). Leaf area ratio and SLA respond not only to the average diurnal temperature, but also to the difference between day and night temperatures (DIF). In tomato, Smeets and Garretsen (1986) reported genotypic differences in SLA in response to DIF. Mean daily temperatures have been found to affect the growth rate of greenhouse tomato (Seginar et al. 1994). In young tomato plants, maximum rate of biomass accumulation occurred at a temperature close to 25°C (Went 1944; Hussey 1965). Hussey (1963) reported that the rates of leaf formation and leaf growth increased at 25°C compared to 15°C. More leaves were formed before flowering at 25°C than at 15°C. The optimum temperature for growth rates in vegetative tomato increases with PPFD levels and CO z concentration and decreases with plant age (Went 1945). Tomato fruit set and fruit weight per plant decreased as mean daily temperatures increased from 25 to 29°C (Peet et al. 1996) In this study, mean daily temperature was more important than either day or night temperatures per se (which ranged from 28-32°C day and 26-22°C


11

night) or the difference between day and night temperatures (which ranged from 2-10°C). Day and night temperatures do not have the same effect on tomato, however. In the vegetative phase, the optimum day temperature for total biomass accumulation is 2SoC, while the optimum night temperature increases from 18 to 2SOC depending on the day temperature (Hussey 1965). In work reported by Heuvelink (1989), day temperature was more important than night temperature in determining the fresh and dry weights, plant length, leaf area, leaf and truss numbers, and RGR of young tomato plants. In the reproductive phase, low temperatures in the range of 10 to 12°C during the early stages of flower development cause cluster branching (Calvert 1966). Low temperatures influence fruit set in tomato by affecting pollen viability (Martinez 1994). Slack and Calvert (1978) found a positive correlation between increasing night temperature and early fruit yield, but final yield was negatively related to temperature. Papadopoulos and Tiessen (1983) reported genotypic differences in the response of tomato flowering and yield to day/night air temperature regimes. Flowering of cv. Ohio MR-13 was delayed significantly at 24°/8°C (day/night) compared to the 24°/17°C (day/night) treatment, but the flowering of cv. Vendor was unaffected by air temperature treatments. Marketable yield of cv. Vendor was significantly higher at 24°/8°C compared to the 24°/17°C treatment, while the marketable yield of cv. Ohio MR-13 was unaffected. Papadopoulos and Tiessen (1983) suggested that when the day temperature is optimum, night temperature, depending on the genotype, determines earliness and marketable yield in tomato. They further suggested that when the night temperature is low (e.g., 8°C) fruiting in tomato depends heavily on day temperature. Went (1944) also arrived at a similar conclusion based on the observation that normal fruiting occurred at 26°/SoC compared to total absence of fruiting at So/SoC. Gent (1988) found that under a DIF of 9°C, greenhouse tomato fruits grew and ripened quickly, resulting in greater early yield. de Koning (1988) reported a positive effect of increasing night temperature on final fruit yield and fruit size. Several studies (e.g., Langhans et al. 1981; Slack and Hand 1983; Hurd and Graves 1984; de Koning 1990) have suggested that plants grow and develop in response to temperatures integrated over periods ranging from 24 h to several days. Seginer et al. (1994) stated that within certain bounds, plants could tolerate a certain variation about the optimal temperature without negative effects. In sweet pepper, vegetative growth and development depend mainly on the 24-h mean temperature, while the effect of the day/night amplitude is of minor importance (Bakker and van Uffelen 1988). Temperature also affects pepper flowering, fruit set, and fruit growth. Bakker (1989) applied

12


12 temperature regimes ranging from 16°/15°e to 28°/21°C (day/night) temperatures and found that low mean temperatures significantly delayed flowering in sweet pepper. The total number of flowers was significantly related to 24-h mean temperature as well as to day and night temperature amplitude; the high day/low night temperature conditions are considered to affect high flower abortion in the bud. Fruit set is increased by low temperatures. A normal regime for this stage would be 22 to 23°e by day and 18 to 19°e at night (Smith 1979). Bakker (1989) found that the pattern of fruit set and mean percentage fruit set over a long time interval depend mainly on 24-h mean temperature and day/night temperature amplitude. In contrast, Rylski and Spigelman (1982) suggested that night temperature determines pepper fruit set, but the response differs at different day temperatures. Abortion of fruits is related to assimilation rate and distribution. At high temperatures, more flowers are formed and fruit growth is enhanced, implying a high assimilation demand. Under low-light conditions this leads to high rates of abortion of newly formed fruits (Schapendonk and Brouwer 1984) and reduced fruit set. Low 24-h mean temperatures increased the number of fruits per plant while reducing vegetative growth (Bakker and van Uffelen 1988). Further, the presence of fruits reduces vegetative growth even further, resulting in an unfavorable leaf area/fruit ratio at low temperatures (Bakker 1989). Lower sink activity of pepper fruits at low tenlperatures reduces the mean fruit weight (Bakker and van Uffelen 1988), as individual fruit growth largely depends on assimilate supply (Walker and Ho 1977). Low temperatures also disturb fruit development by the absence of seeds and deformation of the ovary (Rylski and Spigelman 1982). The length/width ratio of pepper fruits is reduced by low 24-h mean temperatures (Bakker 1989). The formation of well-shaped, elongated fruits in sweet pepper requires that night temperatures be high (18 to 20°C) during flower development and low (8 to 10 0 e) thereafter (Rylski 1973). The net result ofthese responses is that temperature strongly affects the mean fruit weight as well as the yield of high-quality fruits (Bakker and van Uffelen 1988; Bakker 1989). Cucumber requires higher temperatures than tomato or sweet pepper for optimum plant growth. According to Friend and Helson (1976) and Karlsen (1978), the maximum rate of biomass production is achieved at a constant air temperature of 30 to 35°C, whereas the optimum temperature for the rapid expansion of leaves is 25°C (Milthorpe 1959). Slack and Hand (1983) observed that cucumber plants at the transplanting stage propagated at 24°/17°e day/night temperatures were 17% taller, 17% heavier (on biomass basis), and had 6% more leaf area than plants grown at 21°/19°C day/night temperatures. Rates of stem extension, leaf


13

area expansion, earliness, and weight of fruits from early and final harvests are linearly related to 24-h mean temperatures in the early postplanting period (Slack and Hand 1983). Temperature affects not only plant growth but also flower formation and abscission in cucumber (Manrique 1993). Although flower abscision occurs at all temperatures, flower numbers are more persistent at low temperatures (e.g., 15°C) than at high temperatures (e.g., 27°C) because of the increase in competition between buds at increased temperatures (van der Vlugt 1983 a and b). Grimstad and Frimanslund (1993) reported that an average daily temperature of 15 to 25°C reduced the time to the first cucumber harvest by 1.6 d °C-1 and increased the average total yield during the first 8 weeks after transplanting by 0.54 kg m-2 °C-1 over crops raised at 15°C. Raising the 24-h mean temperature during the early postplanting stage increased total yield by 1.17 kg m-2 for each 1°C (Slack and Hand 1983). Grimstad and Frimanslund (1993) reported that the difference between day and night temperatures had no effect on cucumber fruit yield but improved fruit quality. Temperature affects the sink strength of individual organs (Bakker 1995), which allows for the regulation of biomass partitioning in greenhouse tomato (Marcelis and de Koning 1995). Low temperatures have been shown to prevent the export of assimilates from the leaves (Acock and Pasternak 1986). At prolonged low temperatures, flower development, fruit set, and fruit growth are more adversely affected than vegetative growth (Bakker 1995). Tomato plants could easily survive temperatures below 10°C, but for fruit set this temperature is the low limit (Picken 1984). Temperature is a major regulator of developmental processes (Cockshull 1992). High temperatures increase the rates of leaf initiation and appearance (Milthorpe 1959) as well as the maturation rate of organs (Bot and Challa 1991). Higher temperatures in the early stages of growth of greenhouse tomato promote leaf expansion and, thus, light interception and also flowering and fruit development (Cockshull1992). 3. Humidity. Grange and Hand (1987) concluded that humidity between 0.2 and 1.0 kPa VPD (90 to 55% relative humidity, respectively) did not affect the growth and development of greenhouse crops. According to Picken (1984), pollination was similarly little affected over the same range. Extremely low humidity (VPD > 2 kPa) can lead to high transpiration and reduced photosynthetic rates. High humidity «0.2 kPa), which is considered more important than low humidity in greenhouses (see later),

14


has a significant impact on the energy balance of crops. Elevated humidities suppress crop transpiration, a process that converts a major fraction of incoming solar radiation into latent heat (Stanghellini 1987). Decreasing this fraction temporarily results in high leaf temperatures (Bakker 1995). Crop transpiration involves the passage of water vapor through the leaf stomata and the aerodynamic boundary layer of the leaf to the greenhouse air, which leads to an increased humidity (Bailey 1995). Transpiration is determined by (a) vapor pressure differential between leaf tissue and air and (b) resistances in the stomatal and boundary layer to vapor transport between leaf and air. Stomatal resistance is affected by radiation, CO 2 concentration, air humidity, and crop water status, whereas boundary layer resistance depends on greenhouse air speed (Bot and Challa 1991). When cornbined with the strong correlations found among radiation, temperature, and humidity within the greenhouse, these factors result in a linear relationship between transpiration and radiation (Stanghellini 1994). The ratio between transpiration and incoming radiation is affected by crop leaf area, season, and greenhouse type (Stanghellini 1994). The major long-term effect of humidity on greenhouse crops is through its effect on leaf area (Bakker 1991). Leaf expansion is favored by high humidity (through an improved water balance), but local Ca deficiency caused by suppressed transpiration rates can result in reduced leaf area (Bakker 1990; Holder and Cockshull1990). de Kreij (1995) reported that in cucumber at a VPD of 0.3 to 0.4 kPa, leaf area was 10% larger than at a VPD of 0.9 kPa; in tomato, high humidity (VPD < 0.45 kPa) in winter or early spring caused a low leaf area which negatively influenced production, while high humidity during the day in summer (VPD = 0.33 kPa) caused no difference in production compared with a low humidity (VPD = 0.76 kPa) during the day. At high daytime humidity, the incidence of blossom-end rot in tomato was lower than at low daytime humidity. In sweet pepper, humidity had no effect on total leaf area. There are differences among the three vegetable crops in the response of final yield to humidity. Bakker (1988) reported that the yield of cucumber was increased by high humidity in the day (VPD 0.57 to 0.91 kPa) but was unaffected by humidity at night (VPD 0.26 to 0.66 kPa) or by the 24-h mean humidity (VPD 0.43 to 0.75 kPa). In tomato, final yield was reduced by high humidity at night (VPD 0.21 to 0.71 kPa) or 24-h mean humidity (VPD 0.2 to 0.8 kPa). Daytime humidity (VPD 0.35 to 1.0 kPa) had no significant effect (Bakker 1990). Bakker (1989) found that sweet pepper yield did not respond to humidity by day (VPD 0.33


15

to 0.79 kPa) or by night (VPD 0.27 to 0.86 kPa) nor to 24-h mean humidity (VPD 0.30 to 0.78 kPa). Although the effects on final yield differed between the three crops, in all cases fruit quality at harvest was reduced by high humidity. For example, Bakker (1988) found that cucumber fruit color at harvest was 6.5 (9 = dark green; 1 = yellow) in plants grown at high humidity compared to 7.0 in those grown at low humidity. Low humidities have also been reported to cause reductions in fruit growth rates. In tomato grown in nutrient film culture, Pearce et al. (1993) observed reduced fruit expansion rates during the middle of the day. Since water supply was not limited, water taken up by the plants was used to meet transpiration requirements rather than to expand fruits. In cucumber seedlings, RGR increased in response to high humidity (reduced VPD) (van de Sanden and Veen 1992). Bakker (1991) reported a small but significant increase in RGR in response to an increase in daytime humidity for tomato seedlings. Van de Sanden and Veen (1992) reported that the mechanism underlying the rise in RGR with increasing humidity depended on the VPD. At VPDs between 0.8 and 1.4 kPa, the effect on RGR was attributed to an increase in NAR, caused by an increase in stomatal conductance; at low VPD (0.2-0.8 kPa), RGR was affected by an increase in SLA. Burrage (1988) also observed an increase in SLA for tomato plants at high humidity. In tomato seedlings, Bakker (1991) attributed the effect of humidity on RGR to the small increase in NAR as LAR was unaffected. In cucumber, unlike in tomato where SLA was unaffected, high humidities resulted in an increase in SLA (Bakker 1991). In cucumber grown in a double-inflated polyethylene film-covered greenhouse (D-poly, mean daytime VPD = 0.41 KPa), Papadopoulos and Hao (1997) found the SLA to be 0.034 m 2 g-l as compared to the 0.023 m 2 g-l (p < 0.05) in plants grown under glass cover (mean daytime VPD = 0.58 KPa). Papadopoulos and Hao (1997) concluded that the greater SLA is an adaptive response by the crop to raise the PPFD interception efficiency in response to the low PPFDs found in D-poly houses (PAR transmissions for D-poly and glass cover materials were 55.7 and 62.6%, respectively) for early and final yields were similar between plants grown in the two types of greenhouses. In greenhouses, high humidity is a major concern in connection with fungal and bacterial diseases (Bailey 1995). For example, Winspear et al. (1970) reported that the incidence of Botrytis cinerea on greenhouse tomato can be reduced considerably by reducing the relative humidity to 75% compared with 90%. The incidence of ghost spot caused by B. cinerea on tomato fruit decreased from 1.6 to 0.20/0 when relative humidity was reduced from 90 to 75 %. As liquid water is a pre-

16


requisite for spore germination in most fungal pathogens and since high humidity inside the greenhouse promotes condensation on the crop (Hand 1988), fungal diseases develop. The prevention of high humidities and consequent condensation on the plants is, therefore, the key to preventing fungal diseases within greenhouses (Jarvis 1992; Bailey 1995; Bakker 1995). Recently, the influence of humidity on predator/parasite-pest systems has received much attention as biological control methods become more prominent in integrated pest management schemes. The impact of the greenhouse aerial environment on shoot diseases and predator/ parasite-pest systems for insect pests is discussed in Section IV. 4. Carbon Dioxide. The role of CO 2 enrichment in protected cultivation has been reviewed by Porter and Grodzinski (1985) and Mortensen (1987). Crop responses to CO 2 enrichment in greenhouses suggest that

CO 2 affects photosynthesis, growth, and yield by decreasing the O 2 inhibition of photosynthesis in plants. The optimal CO 2 concentration for growth and yield seems to lie between 700 and 900 JlI L-1. Hurd (1968) estimated that CO 2 enrichment at 1000 JlI L-1 produces an effect similar to an increase of 30% in winter light. Elevated CO 2 concentrations increase the optimal growth temperature. The positive effects of CO 2 on greenhouse vegetable crops are increased plant height, number of leaves, and lateral branching; advanced flowering date; high fruit numbers; high fruit yields; and better-quality fruits (Mortensen 1987). Leaves of CO 2-enriched plants are usually thicker, resulting in a lower SLA and LAR. The effects of CO 2 on growth and production as observed by Nederhoff (1994) in greenhouse cucumber, tomato, and sweet pepper are summarized in Table 1.1. Growth and production responses of these crops to CO 2 enrichment was explained by Nederhoff (1994) by using sink/source relationships. In cucumber, the growth of lateral shoots and a short fruit growth period allow sink strength to adapt rapidly to changes in assimilate supply; this removes the need for biomass storage in vegetative organs. In consequence, and in contrast to sweet pepper and tomato, CO 2 enrichment has no effect on leaf area, SLA, or vegetative biomass in cucumber (Table 1.1). In tomato, at any given time, flower number is near maximum, preventing an increase in fruit number by high CO 2 ; thus, sink establishment is hardly affected by high CO 2 , During periods of high CO 2 assimilation rates, assimilate supply may exceed the demand because the limited fruit numbers in combination with the long fruit growth period lead to assimilates being stored in stems and leaves; thus, SLA decreases. As biomass allo-


17

Table 1.1. Summary of CO 2 effects on growth and production as observed by Nederhoff (1994) in cucumber, sweet pepper, and tomato. Symbols: no tendency; i increase; Jdecrease. CO 2 Effects Crop

LAI

SLA

Leaf Biomass

Stem Biomass

Fruit Production

Cucumber Pepper Tomato

JJ-

JJ-

JJ-

J,

i i i

i

Average Allocation Fruit Weight to Fruits

i i

i i

cation is regulated by sink strength, it is not changed by CO 2 supply. In sweet pepper, fruit set increases under high CO 2 , shifting biomass allocation toward fruits. As fruit growth inhibits vegetative growth and formation of new fruits, sink strength is fixed and cannot adapt to increased assimilate supply as in cucumber. During periods of abundant assimilate supply, these assimilates are stored in stems and leaves, explaining the lower SLA in sweet pepper at high versus low CO 2 supply. Long-term CO 2 enrichment can lead to reductions in leaf area and decreases in SLA (Nederhoff et al. 1992; Nederhoff 1994). High CO 2 supply has been reported to cause partial stomatal closure (Nederhoff 1994) and reduces the transpiration of greenhouse crops (Mortensen 1987; Nederhoff 1994). An extreme form of morphological adaptation of the tomato canopy to CO 2 enrichment is the "short leaf syndrome" thought to be caused by reduced Ca+ 2 translocation at high CO 2 levels (Nederhoff 1994). As Ca+ 2 is transported with the transpiration stream, a reduction in crop transpiration can also reduce Ca+ 2 translocation in the plant (Nederhoff 1994). In the three greenhouse vegetable crops under discussion, increasing the CO 2 concentration from 300 to 1200 tll L-1 reduced crop transpiration, on an average, by less than 7% (Nederhoff et al. 1992; Nederhoff and de Graff 1993). Yelle et al. (1990) found the beneficial effects of CO 2 enrichment (e.g., increases in RGR and NAR) to decline after 10 weeks of exposure to increased CO 2 concentrations. Behboudian and Lai (1994) reported lower concentrations (biomass basis) of macronutrients in tomato plants exposed to 1000 tll L-1 CO 2 compared to the control plants (e.g., 2.57 ± 0.12% N at 340 tll L-1 vs. 1.42±0.05 % Nat 1000 tll L-1). Nederhoff (1994) proposed two possible mechanisms to explain this side effect of CO 2 enrichment. The first mechanism is concerned with the negative (but small) effect of high CO 2 on transpiration rate with reduced translocation of nutrients as a possible

18


consequence. The second mechanism relates to the "diluting effect" of biomass production at high CO 2 concentrations. High CO 2 enhances biomass production, and if nutrient uptake lags behind biomass production, nutrient concentration in the biomass will decrease. B. Root Environment Jensen and Collins (1985) and Papadopoulos (1991, 1994) have described the various soilless media suitable for greenhouse crop production. The most popular soilless tomato production systems are those based on rockwool-type media or the recirculating systems such as the nutrient film technique (NFT). Soilless crop production requires that an adequate supply of all the elements essential for plant growth be maintained at all times. In circulating systems such as NFT, this is achieved by using a combination of automated control of solution electrical conductivity, periodic chemical analysis, and changes in the formulation of the fertilizer concentrations suited to the changing nutritional needs of the crop. A complete description of the root environment under NFT has been given by Graves (1983). An general overview of the role of macro- and micronutrients on the growth and development of greenhouse crops can be found in Joiner et al. (1983) and Papadopoulos (1991, 1994). Fertigation, the application of nutrients through the irrigation system, is a popular method in greenhouse vegetable cultivation. Fertilizer formulations and fertigation schedules for various soilless tomato and cucumber production systems have been published (e.g., Sonneveld and de Kreij 1987; Papadopoulos 1991, 1994). The fertigation solution is usually held at an electrical conductivity ranging between 2000 and 3000 JiS cm-1 , depending on crop stage, which allows the nutritional requirements of greenhouse vegetable crops be met satisfactorily. The pH of the fertigation solution is controlled at 6 to 6.5 to ensure that phosphates and trace elements remain in solution. Currently, computer-controlled fertigation systems, which take into account crop and environmental conditions, (Papadopoulos and Liburdi 1989) are becoming popular in many European and North American greenhouse vegetable enterprises. IV. INTEGRATED MANAGEMENT OF THE CROP A. Environmental Management The environmental factor that is usually not controlled within a greenhouse is radiation. It is often allowed to fluctuate with the outside solar


19

radiation and can be a disturbance to the greenhouse crop system (Garzoli 1985). The net rate of heat gain within a greenhouse as given by Garzoli (1985) is: [Eq.3] where N = net rate of heat gain by the greenhouse (W); r = average transmission of the cover to solar radiation; a = average solar absorption of greenhouse contents; F 1 = factor accounting for the reflection of internal solar radiation by the cover; F z = factor accounting for the absorbed solar radiation used by the crop in photosynthesis; A f = floor area of the greenhouse; H = outside solar radiation (W m-Z); U = heat loss coefficient that accounts for ventilation, convection, condensation, and thermal radiation (W m-z K-l); A c = total surface area of the greenhouse cover (m Z); T ai = inside air temperature; Tao = outside air temperature. As the absorption of solar radiation exceeds the heat loss through the cover, greenhouse temperature rises until the daytime set point is reached. The net rate of heat gain within a greenhouse results in a canopy temperature at which the energy input is balanced by losses due to transpiration and sensible heat loss (Stanghellini 1994). The temperature of the sunlit canopy has been reported to rise to 10°C higher than the surrounding air (Bakker 1995), suggesting that greenhouse crops endure a wide range of operating temperatures. However, the responses of plant processes to temperature may vary. As Cockshull (1992) reported, a venting temperature (see later) of 26°C instead of 21°C can hasten fruit ripening and increase early yields in tomato, but it will also increase the proportion of poor-quality fruits. Stanghellini and Bunce (1993) found little response of tomato leaf photosynthesis to increases in PPFD at a leaf temperature of 18°C, but at 32°C leaf photosynthesis rose with an increase in PPFD. Therefore, the rise in leaf temperature might not be as detrimental as could be expected. There is increasing evidence that the growth and yield of tomato is closely related to temperatures integrated over a 24-h period, possibly longer, rather than to set point day and night temperatures (Cockshull 1992; Bakker 1995). Further, the crop can integrate continually changing temperature (Bakker 1995). Peet et al. (1996) reported that in determining percentage fruit set and total number and weight of fruit per plant in tomato, DIF and the specific day-night temperatures were not as important as the mean daily temperatures. Control of short-term deviations in greenhouse temperature is, therefore, of low priority for a more efficient use of resources.

A. P . PAPADOPOULOS et al.

20

As the greenhouse air temperature reaches the daytime temperature set point and the greenhouse continues to accumulate heat at a greater rate than heat is lost, heat must be removed from the greenhouse (Garzoli 1985), usually by venting. Opening the ventilators increases the risk of diseases and insect infestation and reduces the effectiveness of biological control (Bot 1992). In many greenhouses, the CO 2 injector is not run if greenhouse air temperature exceeds the ventilation set point. In a ventilated greenhouse, Goldsberry (1986) reported CO 2 concentrations of less than 200 III L-1 under moderate radiation and about 250 III L-1 under high radiation. At these concentrations, CO 2 fixation by the crop will be reduced with little opportunity for compensation. At these low CO 2 concentrations, stomatal resistance has been shown to decrease 50%, resulting in large evaporative demands, a condition accentuated by the high radiation and temperatures found in summer (Stanghellini 1994). In many greenhouses, however, CO 2 concentrations are maintained at outside levels when the ventilators are open, a practice that might not always be economical and so ventilators must be allowed to open only when CO 2 concentration reaches a preset value. According to Bailey (1995), economically optimum CO 2 concentration will be that at which the marginal cost of raising the CO 2 concentration is equaled by an increase in crop value. The form of greenhouse environmental control that maximizes the economic performance has been termed optimal control (Challa 1988; Bailey 1995). Two types of models are crucial to assess the financial benefits of a rise in photosynthesis due to CO 2 enrichment (Bailey 1995): (a) Crop models are required to calculate the amount of assimilates obtained from canopy photosynthesis that translates into marketable yields and economic returns, and (b) greenhouse physical models are required to estimate the air leakage rate through ventilators to arrive at the cost of CO 2 supply. Ehler and Karlsen (1993) have proposed a model-based expert system for the optimization of CO 2 enrichment for greenhouse pepper. In their approach, net canopy photosynthetic rate (P - g CO 2 m- 2 h- 1 ) was calculated using a simple big-leaf model of Ehler (1991) in which P was calculated as a function of PPFD and CO 2 levels. The growth rate was calculated according to Eq. 1 and expected income, Ie' as: Ie = G(EDMI)

[Eq.4]

where G = growth rate and EDMI = sales value g-l crop biomass. The cost of CO 2 injection (CJ for attaining a certain CO 2 concentration was calculated as,


Cj

=

Price of CO 2 (v + t - s + P)

21

(Eq. 5)

where v = amount of CO 2 lost to or gained from the surroundings by ventilation; t = amount of CO 2 required to attain a desired concentration; and s = amount of CO 2 developed by the soil. Ventilation is not only important as a means to limit temperature inside a greenhouse; in combination with crop transpiration and cover surface temperature, it also determines the vapor content of greenhouse air. The condensation of water vapor on the cover is determined by the VPD and the temperatures of the greenhouse air and the cover (Bot and Challa 1991). If the temperature of the cover is lower than the dew point temperature of the greenhouse air, condensation will occur (Garzoli 1985). If the temperature of the cover inner surface is higher than the dew point temperature of the greenhouse air, the humidity within the greenhouse tends to rise, especially when ventilation is low (Stanghellini 1994). Mathematical models that relate greenhouse air humidity to crop transpiration (e.g., Stanghellini 1987; Aikman and Houter 1990) as well as yield (Jolliet et al. 1993) have now been developed. This opens the possibilities of controlling crop environments based on either transpiration or humidity (Cockshull1992). The effect of high humidity on tomato growth and yield is delayed in its expression, for it first has to reduce leaf size (Cockshull1992). In the U.K., although high humidity was observed between January and February, its effect was not seen until April and May when the value of the crop was less than premium (Cockshull1992). Stomata of most species open in response to increasing humidity (Stanghellini 1994). An intensive study by Bakker (1991) into the effects of greenhouse humidity on tomato, cucumber, sweet pepper, and eggplant found no effect of humidity on total biomass, indicating no enhancement of photosynthesis due to the commonly observed increase in stomatal conductance for CO 2 , Conditions of high humidity and low transpiration are causes of worry for growers, however, because crops growing under these conditions are often weak plants, sensitive to pests and diseases and to sudden changes in environmental conditions (Bot and Challa 1991). Consequently, many ways of optimally controlling humidity have been proposed, but ventilation may be the most effective method (Bailey 1995). Jacobson (1987) suggested that venting be based on the length of time the greenhouse can remain at 100% humidity without serious danger of diseases. When solar radiation diminishes in the evening, the greenhouse cools down to its nighttime set point value (Garzoli 1985). In most climates,

22


heat must be supplied to maintain this temperature which, in many instances, may not be cost-effective. Night temperatures may influence crop and fruit-growth rates in greenhouse tomato (see Section IILA.2). Greenhouse environmental control systems are an integral part of greenhouse crop production and are used to modify the greenhouse aerial and root environments to suit the physiological requirements of the crop. Since the 1980s, most greenhouse vegetable enterprises have installed computer-controlled environmental systems for multivariable control of the aerial environment. Environmental control computers repeatedly read the inside and outside sensors, determine how close the environmental variables are to the set points, and manipulate the environmental control equipment including heaters, vents, fans, and misting systems. The computational processes used to decide how to manipulate the environmental control equipment are known as control algorithms. Since the actual conditions are compared with the desired conditions, greenhouse environmental control algorithms are classed as feedback or closed-loop control algorithms. Control algorithms have to be fine-tuned to provide smooth dynamic response for a given greenhouse. Udink ten Cate (1983) developed adaptive greenhouse control algorithms that automatically adjust themselves as the dynamics of a greenhouse change throughout the cropping season. B. Pest and Disease Management

Notwithstanding the advanced environmental control systems available to greenhouse vegetable growers (Jewett et al. 1996; Kamp and Timmerman 1996), arthropod pests and plant diseases continue to reduce yields and quality (Powell 1982; Zinnen 1988; Jarvis 1989, 1992; Chase 1991; Shipp et al. 1991). Many growers rely on a chemical pesticide program to reduce a pest or disease outbreak (Shipp et al. 1991). Most pathogens and arthropod pests sooner or later develop tolerance to pesticides (Staub 1991). Pesticide applications also stress the crop and pollute the environment. Little conscious effort toward manipulating the environment to manage arthropod pests and diseases has been employed, however. As Regev (1984) and De Waard et al. (1993) have pointed out, the reliance on pesticides has to be replaced by rational biological control measures (Chet 1987; Jarvis 1989, 1992) which integrate arthropod pest and disease management with the manipulation of the greenhouse environment for crop production. Biological control is the destruction or suppression of arthropod pests and pathogens by the introduction, encouragement, or artificial increase of their natural enemies (Metcalf and Metcalf 1993). As Jarvis (1989)


23

pointed out, biological control agents have unique environmental requirements which mayor may not coincide with the optimum environment for crop production within the greenhouses. Control agents also have their own antagonists and parasites which in turn have environmental requirements. Integrated crop management, in essence, is an exercise in reconciling the greenhouse environment (aerial plus root) required for optimum crop production and the activity of biological control agents with that required for reducing pest activity. 1. Pest. Integrated pest management, in which biological control is combined with chemical and other measures for the control of pests, has been reviewed by Sunderland et al. (1992) for arthropod pests of greenhouse crops in Northern Europe. In this section, we discuss how greenhouse environmental management can be combined with integrated pest management for better crop protection. Irradiance, temperature, and humidity levels within greenhouses have a significant impact on the biology and dispersal of insect and mite pests and their biological control agents and the predatory/parasitic interactions between them. At irradiance levels less than about 17 W m- 2 usually found within canopies, Encarsia formosa Gahan, a parasite of greenhouse whitefly, exhibits decreased fecundity and increased adult mortality (Scopes 1973; Parr et al. 1976). Other biological control agents are not effective under short photoperiod regimes because the agent enters a state of reproductive diapause. Orius insidiosus (Say), a predatory anthocorid that is used to control western flower thrips, enters diapause when day lengths decrease to 12 to 13 h (Ruberson et al. 1991). Also, the predaceous midge, Aphidoletes aphidimyza Rondani, which is a control agent for aphids, enters diapause under similar conditions (Gilkeson and Kein 1981). Gilkeson and Hill (1987), however, report that diapause can be prevented when using a 100 W incandescent bulb every 22 m at a 9/15 h light/dark photoperiod regime. It is not only the biological control agents that can be affected by photoperiod; in North America, two-spotted spider mites enter diapause in November and resume activity again in February and March (Lindquist and Rowe 1984). Of the three above-mentioned environmental factors, the influence of temperature is the most studied. Temperature can have a substantial effect on the developmental rate of an insect or mite. An example is that the life cycle from egg to adult for two-spotted spider mites can be completed in 14.5 d at 21°C, but needs only 3.5 d at 32°C (Scopes 1985). Greenhouse temperature can also influence the effectiveness of a biological control agent in controlling a pest. Phytoseiulus persimilis Athias-Henriot, a predatory mite for spider mites, is an effective control

24


agent at temperatures between 20 and 30°C, but above 30°C, the spider mite population increases faster than that of P. persimilis (Scopes 1985). The optimal temperature for control of whiteflies using E. formosa is in the mid-20°C range (van Lenteren et al. 1996). Van Vianen et al. (1988) reported that the dispersal speed of whitefly in the greenhouse varies according to temperature from 17 to 30°C, with the greatest dispersal speed at the highest temperatures. Greenhouse temperature and irradiance can also indirectly influence the effectiveness of biological control of a pest by affecting the physical surface of the plant. Nihoul (1993) found that increased temperature and irradiance results in an increased number of trichomes per tomato leaf. The result was that more of the predatory mite became entangled in the sticky trichome exudates on leaves that had a greater density of trichomes. The spider mites were less affected and thus their population increased faster than that of P. persimilis. The effect of humidity on predator/parasite-prey interactions and biology is the least understood of the three variables. Milliron (1940) reports that the greatest percentage of whitefly parasitism by E. formosa occurs between 50 and 70% relative humidity. Extremes in relative humidities (down to 31 % and up to 100%) decrease the fecundity and longevity of E. formosa (Kajita 1979). Bauerle et al. (1987) found that misting greenhouse plants to maintain 80% relative humidity, compared to no humidity control, increases the effectiveness of E. formosa. At relative humidities below 60%, the searching capacity, survival, and egglaying rate of P. persimilis (Stenseth 1979; Pralavorio and Rojas 1980; Nihou11993) decrease greatly. Fungal pathogens, such Verticillium lecanii (Zimmerman), Aschersonia aleyrodis Webber, Paecilomyces fumosoroseus (Wize) Brown & Smith, Beauveria bassiana (Bal.), and Metarhizium anisopliae (Metsch) Sorokin show great potential as biological control agents for greenhouse pests (aphids, thrips, and whiteflies) (Brownbridge 1995; Vestergaard et al. 1995; Helyer 1993; Fransen 1990) but their development is highly dependent on greenhouse environment, especially humidity. V.lecanii is commercially available as Mycotal® and Vertalec®, and some of the other products are likely to be commercially available soon. Humidity plays a crucial role in spore germination and infection rates and, hence, in the success of these products as control agents. Relative humidities in the range of 85 to 95% must be maintained for a minimum of 10 to 12 hid (Hall and Burges 1979) and some species of entomopathogens require even longer periods of high humidity. The problem with entomopathogens is maintaining a microclimate suitable for germination on the insect host without inviting disease outbreaks in the crop from other fungi and bacteria.


25

Oil adjuvants are being investigated as a way to use entomopathogens at lower humidities (Helyer 1993). Increased temperature and VPD can greatly decrease the survival rate for all stages of western flower thrips (Frankliniella occidentalis (Pergande)), especially the first-stage larvae (Shipp and Gillespie 1993). The pupal stage was the most resistant to high temperatures, with 100% survival at all temperatures between 15 and 30°C, but at 35°C the survival rate decreased to 60% at the higher VPDs. With A. cucumeris, the larval stage again had the lowest survival rates. The adult stage had less than 90% survival for all temperatures except when VPD was above 2.8 kPa (Shipp and van Houten 1996), where fewer survived. Mathematical models have been developed to predict the survival rate of western flower thrips and their predatory mites at any temperature and VPD regime that is encountered in the greenhouse environment. Shipp et al. (1996) have demonstrated that the rate of predation by A. cucumeris on western flower thrips is also influenced by temperature and VPD, with VPD exerting the greater effect. At a constant temperature, the] ate of killed prey decreased when VPD was increased from 0.04 kPa Wil:l minima occurring between 1.24 and 1.44 kPa. As VPD was increaf:'"d beyond this range, the rate of predation increased again. The optim,jj rates of predation by A. cucumeris on western flower thrips should occur when the VPD ~ 0.75 kPa at recommended greenhouse production temperatures of 17 to 25°C. In the western flower thrip biocontrol complex, the influence of greenhouse environment on pest management is not restricted to the growing season but extends into crop clean-up and preparation for the next crop. In one study (Shipp and Gillespie 1993), between-crop temperatures of 30, 35, and 40° ± 1°C were evaluated and VPDs were maintained as high as possible. For western flower thrips on cucumber and sweet pepper, 40°C and 4.76 kPa provided 90 to 100% control after 2 to 3 d. At 30 and 35°C, 100% control was never reached or took 8 d for 35°C and 3.23 kPa for sweet pepper. Similar results were seen for adult whiteflies on cucumber and sweet pepper. Between-crop temperatures of 35 and 40°C gave 100% control within 3 d. At 30°C and 2.23 kPa, however, 100% control was never achieved. In the case of tomato, all treatments where the 24-h mean temperature and VPD were above 30°C and 1.05 kPa, respectively, provided total control of adult whiteflies. 2. Disease. In manipulating the environment to manage diseases within greenhouses, the key fact is that virtually all bacteria and fungi either infect shoots, flowers, and fruit via a water film or enter stomata directly into the wet substomatal cavity. Infectious conidia of the ubiquitous

26


Botrytis cinerea Pers. :Fr. germinate in a water film within 5 to 8 h, depending on the temperature and the adjacent microflora (Verhoeff 1980). Powdery mildew fungi, long regarded as capable of infecting dry surfaces (Yarwood 1957), have more recently been shown to be dependent on water for infection (De Long and Powell 1988; Powell 1990). The microclimate within about 50 pm of the plant surface is therefore of paramount importance (Burrage 1971). The greatest danger occurs when the dew point is reached and dew persists for only a few hours. The difficulty of monitoring this boundary zone accurately with commercial sensors up to 1 m away from the plant will be apparent. After the infection process, however, pathogenesis and epidemiology are very complicated and vary with crop and pathogen. Conidia of powdery mildew form during the night and disperse in dry conditions during the day (Butt 1978), while Botrytis conidia are dispersed in conditions of rapidly changing humidity (Jarvis 1980) or during worker activity (Hausbeck and Pennypacker 1991). Several diseases are characterized by a period of quiescence, or latency, following infection (Jarvis 1994), so that remedial actions when the symptoms appear might be days or weeks too late. Gray mold lesions on the stems of tomato plants can appear 10 to 12 weeks after deleafing, the period when the microclimate should be kept dry and inoculum removed (Wilson 1963). When soilless substrates and the NFT were introduced in the 1970s, it was thought that root diseases would be eliminated. Experience has shown that this is not so; indeed, severe losses from a variety of root diseases have occurred from time to time in soilless systems (Daughtrey and Schippers 1980; Jenkins and Averre 1983; Zinnen 1988; van der Vlugt 1989; Jarvis 1992). Most outbreaks of disease can be traced to poor hygiene practices, the use of pathogen-contaminated water (Hendrix and Campbell 1973; Erwin et al. 1983), or the transfer of pathogens by insects (Gardiner et al. 1990; Goldberg and Stanghellini 1990; Jarvis et al. 1992). In spite of this, excellent yields of high-quality produce are obtained in hydroponic systems. Root disease levels tend to decline as the crop ages because hydroponic systems start with little or no natural biological control, and potential antagonist microorganisms take some time to build up to effective populations (Cook and Baker 1983). McPherson and Harriman (1994) considered that, given time, an equilibrium between the plant, its pathogens, and their antagonists could be attained, however. It might be supposed that given the degree of environmental control that can be achieved in the greenhouse, biological control of plant diseases (Cook and Baker 1983; Chet 1987; Andrews 1992) might be suc-


27

cessful. Experience has proven otherwise. Only a few commercially successful microbial antagonists can be applied to greenhouse crops (Jarvis 1992). Development of a decision-support tool to better manage the greenhouse environment for crop growth, impede pathogen activity, and enhance the effectiveness of biological control agents may improve the situation. The prerequisites for a decision-support tool for integrated management of greenhouse crops are discussed in the next section. Jarvis (1989, 1992) reviewed greenhouse management measures for pest control including scrupulous greenhouse hygiene and the eradication of inoculum sources. To this can be added the need to eradicate arthropod and other vectors of pathogens. Inoculum eradicant measures include steam sterilization of soil and other substrates (Hege and Ross 1972; Nederpel 1979) or, preferably, pasteurization using heated airsteam mixtures (Baker and Roistacher 1957), solarization (Katan 1981), or fumigation with registered volatile chemicals (Vanachter 1979). The initial inoculum can also be considerably reduced or avoided by strict observation of quarantine practices at international, regional, and even at the local greenhouse levels; the use of disease-free seed and other planting material; roguing infected plants as soon as they are seen in a crop; and grafting onto disease-resistant rootstocks (Jarvis 1989, 1992). Genetic resistance is a primary means of disease control in greenhouse vegetable production. The downy mildew pathogen of lettuce, Bremia lactuceae Regel, exists in at least 24 pathogenic biotypes (Crute 1984; Farrara et al. 1987), and so disease avoidance in any particular greenhouse depends largely on knowing the local pathogen biotype structure. Even so, new biotypes continually appear as, for example, has happened with Verticillium dahliae Kleb.; race 2 which recently appeared in Ontario greenhouses on tomato cultivars with the Ve gene for resistance to race 1. It had apparently spread from neighboring fields (Dobinson et al. 1996). Crops stressed by adverse environments (Levitt 1980; Eastin and Sullivan 1984) generally are more susceptible to diseases (Schoenweiss 1975). Vegetable crops with the high fruit loads obtained in hydroponic culture seem particularly prone to new pathogens. Thus, in recent years Penicillium oxalicum Currie & Thorn has become a major pathogen in cucumbers in rockwool (Jarvis et al. 1990; Jarvis and Ferguson 1992) as have Nectria haematococca Berk. and Broome in peppers in rockwool (Jarvis et al. 1994) and powdery mildew (Erysiphe orontii Cast.) in tomato in rockwool and NFT (Belanger and Jarvis 1994). In addition, fruiting stress is also conducive to physiological root death (Daughtrey and Schippers 1980; van der Vlugt 1989).

28

A. P. PAPADOPOULOS 8t al.

V. FUTURE PROSPECTS Greenhouse crop production is the result of complex interactions between crop and environment. Clarke et al. (1994) represented the greenhouse production system as a six-level hierarchy of factors. A change in one production factor can potentially affect the remaining five levels and ultimately the greenhouse crop health. For example, greenhouse climate can affect the toxicity of a pesticide on a biological control agent. The biological control agent in turn affects the population of a pest which might be vectoring a disease. The greenhouse climate can directly or indirectly affect five levels of factors: pesticide, biological control agent, vector pest, disease, and, ultimately, the greenhouse crop itself. Managing the complex greenhouse cropping system requires a multidisciplinary approach that integrates routine cultural practices and environmental and fertigation regimes with pest and disease protection strategies into a common decision-making process. For an integrated crop management approach, modern growers must become experts in interpreting and managing technical information for decision making. This could well be beyond the means of individual growers, thus requiring the use of computer-based decision-support systems (DSS) to manage the information. There are three main reasons for the use of computer systems in integrated crop management: First, computer-controlled environmental systems routinely generate megabytes of data. Add to these greenhouse climate data, crop production data, fertigation records, and pest count records and the data quickly become unmanageable without computer technology. Second, the relationships between the various crop production factors are complex and will require expert knowledge or computer models to simulate and understand their effect on the greenhouse crop. Third, it is likely that many strategies within an integrated crop management framework will conflict. Resolution of these conflicts will require expert knowledge and information on all aspects affecting the greenhouse crop. Ideally, a decision-support system for integrated crop management should accommodate the following three functions: data management and analysis, decision support, and conflict resolution. The DSS should have the capability to store and retrieve greenhouse data, summarize the data, prepare reports, and graphically display data provided by the grower, computerized climate control, fertigation or packing systems, or external databases on bulletin boards or on the Internet. In addition, the DSS should provide support for the grower to make decisions through predictive simulation models and/or expert systems. Finally, the DSS should identify and help resolve conflicts.


29

Several DSSs have been developed for greenhouse applications. Jones et al. (1986) developed an expert system for greenhouse tomato based completely on the knowledge of a grower for choosing climatic set points. Jacobson (1987) described a DSS where crop models were combined with an expert system to choose optimal environmental set points for greenhouse tomato. In this approach, the expert system contained a knowledge base for variables that have not been well modeled, such as the length of time humidity may remain high without a disease outbreak. Dayan et al. (1993) developed a greenhouse tomato model, TOMGRO, that models plant physiological processes and their dependence on environmental conditions but not the effects of pest and diseases on crop productivity. Martin-Clouaire et al. (1993) developed an expert system to determine daily climatic set points for greenhouse tomato while balancing conflicting goals such as avoiding diseases, maintaining crop growth, and minimizing energy expenditures. Clarke et al. (1994) discussed other expert systems for use in greenhouse applications. The Harrow Greenhouse Crop Management System (HGCMS, Clarke et al. 1994) helps the grower manage climate, production, pest, and disease data. The HGCMS can also identify and recommend control and preventive measures for greenhouse cucumber and tomato pests, diseases, and physiological disorders. The system identifies conflicting control measures. Although the systems developed to date are useful for providing solutions to greenhouse crop management problems, the technology is still a long way from being a DSS that provides true integrated crop management strategies. Meeting this goal requires improved understanding of crop response to the environment and formulation of models that describe these relationships mathematically. Models of crop responses to pests and pathogens are required, as is an understanding of the response of pests and their biological controls to the environment. In the interim, since the ecophysiology of pests and pathogens in combination with their parasites or predators is so complex and poorly understood, a DSS along the lines of the HGCMS will be required to store and retrieve pest and disease management information. The DSS also allows growers to input their knowledge on aspects of crop response that the model does not contain. An integrated crop management DSS can be a very useful and powerful tool. For example, data measured by climate sensors in real time could be used within a crop growth model to compute optimal set points similar to that described for CO 2 optimization in Section IV. The DSS could then run a pest and biological control agent model and use expert rules to adjust the set points if they were found to be detrimental to biological control agents or crop. The actual implementation ofthe set


30

points as recommended by the DSS would best be left to the judgment of the grower. LITERATURE CITED Acock, B., D. A. Charles-Edwards, D. J. Fitter, D. W. Hand, L. J. Ludwig, J. Warren Wilson, and A. C. Withers. 1978. The contribution of leaves from different levels within a tomato crop to canopy net photosynthesis: An experimental examination oftwo canopy models. J. Expt. Bot. 29:815-827. Acock, B., and D. Pasternak. 1986. Effects of CO 2 concentration on composition, anatomy and morphology of plants. p. 41-52. In: H. Z. Enoch and B. A. Kimball (eds.), Carbon dioxide enrichment of greenhouse crops Vol. II. Physiology, yield and economics. CRC Press, Boca Raton, FL. Aikman, D. P., and G. Hauter. 1990. Influence of radiation and humidity on transpiration: implications for calcium levels in tomato leaves. J. Hart. Sci. 65:245-253. Ammerlaan, J. C. J. 1994. Environment-conscious production in glasshouse horticulture in the Netherlands. Acta Hort. 361:67-76. Andrews, J. H. 1992. Biological control in the phyllosphere. Annu. Rev. Phytopathol. 30:603- 635.

Bailey, B. J. 1995. Greenhouse climate control-new challenges. Acta Hart. 399:13-23. Baker, K. F., and C. N. Roistacher. 1957. Principles of heat treatment of soil. p. 138-161. In: U. F. Baker (ed.), The uc. system for producing healthy container-grown plants. Calif. Agr. Expt. Sta. Man. 23. Bakker, J. C. 1988. The effects of humidity on growth and production of glasshouse cucumbers, tomatoes and sweet peppers. Acta Hart. 229:159-163. Bakker, J. C. 1989. The effects oftemperature on flowering, fruit set and fruit development of glasshouse sweet pepper (Capsicum annum L.). J. Hort. Sci. 64:313-320. Bakker, J. C. 1990. Effects of day and night humidity on yield and fruit quality of glasshouse tomatoes (Lycopersicon esculentum MilL). J. Hart. Sci. 65:323-331. Bakker, J. C. 1991. Analysis of humidity effects on growth and production of glasshouse fruit vegetables. Ph.D. diss., Agricultural Univ., Wageningen, The Netherlands. Bakker, J. C. 1995. Greenhouse climate control: constraints and limitations. Acta Hart. 399:25-35.

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Crute, I. R. 1984. The integrated use of genetic and chemical methods for control of lettuce downy mildew (Bremia lactuceae). Crop Prot. 3:223-242. Daughtrey, M. 1., and P. A Schippers. 1980. Root death and associated problems. Acta Hort. 98:283-291. Dayan, K, H. van Keulen, J. W. Jones, I. Zipori, D. Shmuel, and H. Challa. 1993. Development, calibration and validation of a greenhouse tomato growth model: I. Description of the model. Agr. Syst. 43:145-163. de Koning, A N. M. 1988. The effect of day/night temperature on growth, development and yield of glasshouse tomatoes. J. Hort. Sci. 63:465-471. de Koning, A. N. M. 1990. Long-term temperature integration of tomato. Growth and development under alternating temperature regimes. Scientia Hort. 45:117-127. de Kreij, C. 1995. Effect of nutrition and climate on production and quality. Canadian Greenhouse Conf., Guelph, Ontario, Canada. Oct. 19-20,1995. De Long, R. K, and C. C. Powell. 1988. Development of a deterministic model for greenhouse rose powdery mildew using modified leaf wetness sensors. Phytopathology 78:1520 (Abstr.). De Waard, M. A, S. G. Georgopoulos, D. W. Holloman, H. Ishii, P. Leroux, N. N. Rassdale, and P. J. Schwinn. 1993. Chemical control of plant diseases: problems and prospects. Annu. Rev. Phytopathol. 31:403-421. Dobinson, K. F., G. K. Tenuta, and G. Lazarovits. 1996. Occurrence of race 2 of VerticilHum dahHae in processing tomato fields in southwestern Ontario. Can. J. Plant Pathol. 18:55-58.

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Erwin, D. c., S. Bartnickin Garcia, and P. Tsao. 1983. Phytophthora: its biology, taxonomy, ecology, and pathology. Am. Phytopathol. Soc., St. Paul, MN. Farrara, B. F., T. W. Hott, and R. W. Michelmore. 1987. Analysis of genetic factors for resistance to downy mildew (Bremia lactuceae) in species of lettuce (Lactuca sativa and L. serriola). Plant Pathol. 36:499-514. Fitter, A H., and R. K. M. Hay. 1981. Environmental physiology of plants. Academic Press, London. Fransen, J. J. 1990. Natural enemies of whiteflies: Fungi. p. 187-210. In: D. Gerling (ed.), Whiteflies: their bionomics, pest status and management. Intercept Ltd., Hants, UK. Friend, D. H. c., and V. A Helson. 1976. Thermoperiodic effects on the growth and photosynthesis of wheat and other crop plants. Bot. Gaz. 137:75-84. Gaastra, P. 1959. Photosynthesis of crop plants as influenced by light, carbon dioxide, temperature and stomatal diffusion resistance. Meded. Landbouw Hogesch., Wageningen 59:1-68.

Gardiner, R. B., W. R. Jarvis, and J. 1. Shipp. 1990. Ingestion of Pythium spp. by larvae of the fungus gnat Bradysia impatiens (Diptera: Sciaridae). Ann. Appl. BioI. 116: 205-212.

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2

Okra: Botany and Horticulture Efta] Duzyaman Department of Horticulture Faculty of Agriculture University of Ege 35100, Izmir, Turkey

I. Introduction II. Botany A. Taxonomy B. Origins and Distribution C. Morphology D. Floral Biology E. Physiology 1. Environmental Requirements 2. Growth and Development 3. Fruit Composition F. Genetics and Breeding III. Horticulture A. Commercial Cultivars B. Cultural Practices 1. Plant Establishment 2. Fruit Set and Harvest 3. Storage 4. Plant Nutrition 5. Irrigation 6. Growth Regulator Treatments 7. Weed Control 8. Pests and Diseases C. Processing 1. Canning and Freezing 2. Drying IV. Research Needs Literature Cited


E. DUZYAMAN

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I. INTRODUCTION

Okra is a traditional vegetable crop commercially cultivated in West Africa, India, Southeast Asia, the southern United States, Brazil, Turkey, and northern Australia and is also a popular home-garden vegetable in many areas. Yearly okra production is estimated to be 4 million t throughout the tropical, subtropical, and Mediterranean climates and contributes about 4% of total vegetable consumption in most developing countries (Siemonsma 1982a). In addition to fruits, leaves are also consumed in some African countries (Charrier 1984; Hamon et al. 1986), and medicinal properties have been reported in some species (Siemonsma 1982a; Velayudhan and Upadhyay 1994). Okra is also known as Lady's Finger in English, gombo in French, bhendi in Hindi, and bamiah in Arabic. Okra has been cultivated in Africa for over 2000 years and domestication probably took place in Egypt, where records date back to Neolithic times (Chevalier 1940; Charrier 1984). Okra is increasing in popularity and is now commonly available as a boiled or fried vegetable dish at restaurants, salad bars, and cafeterias. It has become a new alternative vegetable in the European diet (Quagliotti and Lotito 1989; Possingham 1990). Fresh tender fruits provide dietary fiber, protein, and vitamin C in human nutrition (Table 2.1; Grubben 1977; AI-Wandawi 1983; Candlish et al. 1987). Okra seeds have also gained much interest as a new oil and protein source. Seeds contain 12 to 17% oil, mainly monounsaturated fatty acids (oleic) and palmitic acid (Martin and Rhodes 1983) and have potential in cereal-based diets due Table 2.1. Nutritive value of okra fruit (Grubben 1977; Candlish et al. 1987). Variable

Content (%)

Dry matter Moisture Protein Starch Cellulose Lignin Calcium Iron Carotene Thiamine Riboflavin Niacin Vitamin C

10.4 89.9 1.8 0.52 0.98 0.52 0.09 0.001 0.0001 0.00007 0.00008 0.0008 0.18

2. OKRA: BOTANY AND HORTICULTURE

43

to their high lysine level (AI-Wandawi 1983). Seed flours and protein concentrates are more soluble than commercial soy products and display promise as applications in food products such as meat analogs, soups, and sauces (Bryant et al. 1988). However, okra is considered an economically minor crop, and scant attention is paid to it in international research programs. Research is underway mostly in India and Nigeria and to a lesser extent in the United States. Reviews on okra have covered cultural techniques (Siemonsma 1982a), genetic resources (Charrier 1984; Hamon et al. 1991), and diseases (Mukhopadhyay and Chowdhury 1986; Sokhi et al. 1990). This chapter is intended as an overview of okra from a horticultural perspective.

II. BOTANY A. Taxonomy Okra is a member of the Malvaceae which includes fiber crops such as cotton (Gossypium spp.) and kenaf (Hibiscus cannabinus). The present accepted binomial is Abelmoschus esculentus (L.) Moench (Siemonsma 1982a), formerly Hibiscus esculentus L. (van Borssum Waalkes 1966; Bates 1968). The genus Abelmoschus comprises nine species (IBPGR 1991c; Table 2.2). The relationships and genetic integrity among the cultivated and wild forms of the Abelmoschus species have been studied by Babu and Dutta (1990) and Hamon and Hamon (1991). In most cases, intraspecific crosses among Abelmoschus species are not readily obtained, and F 1 S are often sterile (Siemonsma 1982b; Charrier 1984). However, A. eSGulentus crosses relatively easily with A. caillei (Nerkar and Jambhale 1985; Hamon and Yapo 1986; Fatokun 1987; Jambhale and Nerkar 1989) and may produce partially fertile plants. A. tetraphyllus x A. esclulentus hybrids are also possible (Sharma and Dhillon 1983; Hamon and Yapo 1986; IBPGR 1991c) and have been stabilized for breeding purposes (Koechlin 1991). The variation in chromosome numbers suggests a number of ploidy levels (Table 2.2). Charrier (1984) suggested three ploidy levels, where A. moschatus (n = 36), A. ficulneus (n = 36), A. tuberculatus (n = 29), A. esculentus (n = 36), A. manihot (n = 30-34) are at ploidy level 1; A. esculentus (n = 62-65), A. tetraphyllus (n = 69) are at ploidy level 2; and A. caillei (n = 99) is at ploidy level 3. Four ploidy levels seem also possible (Hamon 1988). The genus, therefore, may be a "polyspecies complex" where continuous interchange of genes throughout itsevolution has complicated the determination of relationships.

~ ~

Table 2.2.

Classification of Abelmoschus.

Species

Chromosome Number

Type of Species

A. esculentus (1.) Moench A. caillei (A. Chev.) Stev. A. moschatus Medikus subsp. moschatus var. moschatus subsp. moschatus var. betulifolius subsp. biakensis (Hochr.) Borss. subsp. tuberosus (Span.) Borss. A. manihot (1.) Medikus A. tetraphyllus (Roxb. ex Hornem.) R. Graham var. tetraphyllus var. pungens (Roxb.) Hochr. A. tuberculatus Pal & Singh A. ficulneus (1.) W. & A. ex Wight

Wild Wild Wild Wild

A. crinitus Wall. A. angulosus WalL ex W. & A.

Wild Wild

Cultivated Cultivated Semiwild Cultivated Wild Wild Semiwild

(2n)

Geographical Distribution (See Fig. 2.1)

108-144 mostly 124 or 130; also 66,72 185-198

1

72

2

? ?

2 2° 2° 3

38 60-68 138 138 58 72 (African sp.) 78 (Asian sp.) ? 56

4 4 5 6 6 7

8

Sources: IBPGR (1991c); chromosome numbers and cultivation from Siemonsma (1982b), Charrier (1984), Hamon and Yapo (1986), and Koechlin (1991).

Area of okra CA. esculentus) cultivation . . . . . . . . .. Centers of genetic diversity of the genus Abelmoschus.

Fig. 2.1. fI:>

VI

The cultivated area of okra and distribution of the genus Abelmoschus in the world (Charrier 1984).

()\)

46

E. DUZYAMAN

B. Origins and Distribution The centers of diversity of Abelmoschus include West Africa (Benin, Togo, Guinea), India, and Southeast Asia (Burma, Indochina, Indonesia and Thailand) (Fig. 2.1; Chevalier 1940; van Borssum Waalkes 1966; Siemonsma 1982a,b; Hamon 1988; Hamon and Hamon 1991; Bisht et al. 1995). Two species, A. esculentus and A. caillei, are cultivated for their fresh fruits. To avoid confusion in the text, the name okra will be used only for A. esculentus which is an annual cultigen in the low-altitude regions of the tropics and subtropics, with an extension to temperate climates in the Mediterranean basin. Abelmoschus caillei (Stevels 1988), a relatively new species, is most probably indigenous to West Africa (Siemonsma 1982b; Hamon et al. 1986). The geographical distribution is from northwest Guinea extending to southeast Cameroon, suggesting it may be distributed in the central parts of Africa. It is cultivated in the most humid parts of Guinea, mostly in an intercropped system with A. esculentus (Hamon and Charrier 1983; Hamon 1988). A. moschatus and A. manihot are semiwild, and show a greater diversity than the cultivated forms (Hamon et al. 1991). A. moschatus is morphologically and genetically the most different from the other species (Hamon and Yapo 1986) with probably the widest geographical distribution (Hamon and Charrier 1983), which extends from the South Pacific Islands through Indochina and India and over to the central and western parts of Africa. The cultivated form (A. moschatus subsp. moschatus var. moschatus), better known as "musk mallow," "Jew's mallow," or "ambrette" in Africa, Asia, and America, has fragrant seeds used for perfume making (Hamon and Charrier 1983). The subspecies biakensis is endemic to Papua New Guinea (Charrier 1984). The cultivation of A. manihot is mainly in Southeast Asia and is known under the vernacular name" aibika"; it is also found in India, northern Australia, and less frequently in the American continent and tropical West Africa. Cultivation is exclusively for leaf consumption. The species A. tetraphyllus (IBPGR 1991c), A. ficulneus, A. crinitus, A. angulosus (van Borssum Waalkes 1966; Bates 1968), and A. tuberculatus (Pal et al. 1952) are truly wild. A. ficulneus is found from the northern parts of Australia to Southeast Asia and from India to most parts of Africa. A. tetraphyllus, A. crinitus, A. angulosus, and A. tuberculatus are exclusively of Asian origin. A. tetraphyllus var. tetraphyllus and var. pungens are endemic to Southeast Asia with extension of the former to Papua New Guinea and New Ireland. A. crinitus is found at low altitudes in India and Southeast Asia, and A. angulosus at high altitudes in India,


47

Sri Lanka, Indochina, and Indonesia. A. tuberculatus is endemic to the northern and western parts of India (Charrier 1984; Velayudhan and Upadhyay 1994). The discovery of A. caillei, the second edible okra species, in West Africa (Chevalier 1940) and later evaluations (Hamon and Yapo 1986; Hamon 1988; Jambhale and Nerkar 1983a, 1989) have received much attention in the last decade. It is distinguished from A. esculentus by shape and number of epicalyx segments and fruit shape and orientation (Siemonsma 1982b), and shows great variability (Hamon and Charrier 1983; Hamon et al. 1991; Koechlin 1991; Ariyo 1993). A. caillei is prized for its potentially prolific yield, vigorous growth, and tolerance to some negative environments, serving as a source of many desirable characteristics for okra (Fatokun 1987; Ariyo 1993). However, it is a short day plant, is very photoperiod sensitive, and requires selection for photoperiod insensitivity to make it more adaptable (Ariyo 1993). In the last decade, much attention has been paid to preservation, characterization, and availability of okra germplasm, one of the main reasons for limited studies on okra breeding. Several okra collection expeditions have been initiated in West Africa, Southeast Asia, and India (Table 2.3). For reviews of earlier okra collection missions, see Charrier (1984), Mergeai (1986), Hamon and van Slaten (1989), Bettencourt and Konopka (1990), Hamon et al. (1991), IBPGR (1991a), and

Table 2.3.

Abelmoschus spp. collection missions in Asia and Africa 1983-1994.

Collection Site Asia Bangladesh India (Mauritius) India India Nepal Sudan (Western) Sudan (Northern) Syria Thailand Africa Benin and Togo Gambela/Ethiopia Guinea Zimbabwe

No. Accessions

20

17 79 181 59 10 18 6

72

718 4

190 25

Reference NBPGR-BARI1990 Damania 1985 IBPGR 1990 IBPGR 1991b Velayudhan and Upadhyay 1994 Hassan et al. 1984 Genief et al. 1985 George 1984 Hamon et al. 1987 Hamon and Charrier 1983 Engels and Dadi 1986 Hamon et al. 1986 Padulosi and Ng 1989

E. DUZYAMAN

48

Koechlin (1991). A descriptor list has been established by IBPGR (Charrier 1984). The joint ORSTOM/IBPGR collection mission during 1982-86 of okra and its wild relatives intensively covered West Africa (Hamon and Charrier 1983; Hamon et al. 1986) and also included Asia (Hamon et al. 1987). Characterization and evaluation of 2283 okra accessions, including A. caillei and A. moschatus, were made. A core collection (180 samples) was also established (Charrier and Hamon 1991) and is available to breeders from the Laboratoire de Resources Genetiques et Amelioration des Plantes Tropicales, ORSTOM, Montpellier, France (IBPGR 1986; Hamon and van Sloten 1989). In West African countries where the local farmers and consumers are not concerned with fruit uniformity, germplasm may be preserved by composting cultivars as a dynamic gene pool to reduce genetic erosion (Akoroda 1986a; Hamon et al. 1986).

c.

Morphology

Commercial okra cultivars are erect annuals, becoming woody at maturity. The main stem branches at the base with usually 2 to 5 but as many as 20 predominant branches/plant. Orthotropic stemmed types are not exclusive (Hamon and van Sloten 1989; Ariyo 1990a; Ariyo and Odulaja 1991). The plant often reaches 60 to 180 cm in height (Hamon and van Sloten 1989; Ariyo 1990a), but an extremely tall type in the central parts of Nepal reaches up to 4 m (Velayudhan and Upadhyay 1994). Leaves are present at each node, solitary flowers are axillary, and fruits are born upright. Simple leaves are palmatifit to palmatisect (Charrier 1984; Ariyo and Odulaja 1991) with a symmetrical lamina of chartaceous texture. The base is cordate, margins toothed (serate), and apex acute (Bhat et al. 1988). Effective methods for leaf area determinations have been proposed by Srinivas (1982) and Abdullahi and Jasdanwala (1991). Red pigmentation can occur in stems, petioles, leaf veins, pedicel, petal bases, and fruits, which gives the plant ornamental value (Martin et al. 1981; More and Vibhute 1983). The plant carries unicellular trichomes on almost all parts of the plant, providing protection from pests such as leafhoppers (Uthamasamy 1985b; Rao 1991). Seeds are relatively large and heavy (60 g/100 seeds) and have a light green to gray color when high in quality (Martin and Rhodes 1983). Shape is round to reniform, and their surface is rather glabrous or sometimes hirsute or scattered, having simple short hairs (trichomes) on the surface (Wyatt 1985). Fruits consist of 55 to 62% pericarp, 30 to 40% seeds, and 7 to 11 % axil (Singh and Agarwal 1988).


49

D. Floral Biology Plants flower 34 to 67 d after sowing. Hermaphrodite golden yellow flowers appear at the 3rd to 19th nodes and generally at the 5th to 7th nodes (Hamon and van Sloten 1989), opening at dawn and remaining open until evening. Flowers have a style in a central position surrounded by a stamen column where anthers are arranged in concentric superimposed circles (5-6 anthers per circle). Stigmas, which are joined in cultivated species, are more or less separated and located much further from anthers. Pollen grains (about 100/anther) are sticky and are not necessarily in contact with the stigma at anthesis. Contact takes place mechanically during the day by elongation of the stamen column (Hamon and Koechlin 1991a). There are 8 to 12 epicalyx segments, linear to lanceolate, surrounding the flower (Chevalier 1940). If floral abortion does not occur, flowers bear erect fruits in each leaf axil starting from the flowering node in both main stem and lateral branches (Hermann et al. 1990). Commercial cultivars have ridged or smooth fruits about 2 cm wide and 10 to 14 cm long at maturity (Ariyo and Odulaja 1991), but there is wide variation in fruit types (Charrier 1984), especially in West African types (Hamon and Charrier 1983; Hamon et al. 1986; Ariyo 1990a). Wild Abelmoschus species have only five carpels (van Borssum Waalkes 1966), but domestication resulted in a higher number of carpels (up to 11) (Hamon 1988). Although okra is assumed to be self-pollinated, hermaphroditic flowers display entomophilous features such as colored petals, nectarin, extrorse dehiscent anthers, and sticky pollen grains (Tenda see Hamon and Koechlin 1991b). Cross-pollination can reach 63%, depending on insect population levels and temperature (Aken'Ova and Fatokun 1984; Akoroda 1986a). Hamon and Koechlin (1991a,b) classified okra as a facultative autogamous species; factors leading to outcrossing are discussed in relevance to flowering behavior and floral morphology. Hybridizing procedures have been established by Koechlin (1991), while the relation of hybrid seed quality to nodal position is discussed by Prabhakar et al. (1985). Large numbers of controlled hybrids may be obtained by depositing pollen on stigma in the morning even without prior emasculation (Hamon and Koechlin 1991b). E. Physiology 1. Environmental Requirements. Okra requires a long growing period (up to 6 months), high temperatures, and high light (Iremiren and Okiy 1986; Ghanti et al. 1991). The vegetative phase is up to 2 months, and a harvest duration of at least 2 to 3 months is required for an economic

50

E. nUZYAMAN

return. The plant is sensitive to frost (Teets and Hummel 1988) and is cultivated as a summer crop in the subtropical and temperate regions. Most okra cultivars require short photoperiods for floral bud initiation (Nwoke 1986). However, there are day-neutral and quantitative long-day genotypes, the latter having a cool temperature requirement for flower initiation (Tenga and Ormrod 1985). If the plant is exposed to high day temperatures, floral development may be delayed. High night temperatures can increase plant height in the majority of the present cultivars (Tenga and Ormrod 1985). The optimum environment for seed production is low precipitation, low relative humidity, and high light with hot, dry weather during seed ripening (Singh et al. 1988; Adetunji and Chheda 1989). Because okra seeds are often sown at suboptimum environments in temperate areas, emergence may be poor (Iremiren and Okiy 1986); therefore, excess seeds are planted (Siemonsma 1982a). Seedling emergence at optimal soil temperature (35°C) (Fasheun 1988) and moisture (Iremiren and Okiy 1986) occurs in 7 days, but at 18/15°C (day/night) about 14 days are required (Lotito and Quagliotti 1991). In the tropics, mulching with straw (e.g., Imperata cylindrica) to reduce soil temperature improved emergence (Fasheun 1988). Sandy-loam soils with good drainage are best suited for okra (Siemonsma 1982a). 2. Growth and Development. Okra has an indeterminate growth habit, but the extent of the fruiting period depends on the combination of the photoperiod sensitivity of the cultivar and daylight duration. A shortday cultivar in the subtropics or temperate regions often will not flower until the first autumnal frosts. Once flowering is induced, day-neutral cultivar plants continue to flower until frost (Teets and Hummel 1988). Fruit production is continuous as the shoot grows so that all transitional stages of development from flower buds to harvestable immature fruit (or mature when left for seed production) appear simultaneously on the plant throughout most of its ontogeny. While the upper parts of the stem(s) remains productive by forming new leaves, leaf senescence occurs at the basal parts (Hermann et al. 1990). High-yielding cultivars have an appropriate relationship between source (leaves and stem) and sink (fruits and flowers) (Rao et al. 1989; Singh and Shyam-Singh 1991), with a high rate of nitrogen translocation and photosynthates partitioning from source to sink (Singh 1990) and bidirectional transport of assimilates to both apical and basal parts of the stem. Prior to flowering, stem and leaves appear to be strong sinks (Rao et al. 1989). Furthermore, fruit removal at early stages (edible fruit harvest) enhances the activity of leaves and apical growth, which enhances


51

fruit production. In contrast, the presence of mature fruits suppresses vegetative growth (Rao et al. 1989). Fruits do not become sinks up to 13 days after pod set (approximately the final elongation stage) (Iremiren et al. 1991), but become the strongest sinks after this date so must be removed punctually to prevent reduction of plant growth (Rao et al. 1989). The importance of frequent and complete harvest for satisfactory yield has been emphasized by many authors. Allowing fruits to mature on the plant, as is the case in seed production (Kanwar and Saimbhi 1987), results in alternate bearing or "fruiting waves," reducing fruit yields/plant by 60 to 70% (Perkins et al. 1952; Akoroda 1986b). 3. Fruit Composition. Fruit composition has importance in consumer quality and has been investigated in detail (Sistrunk et al. 1960; Singh et al. 1990; Iremiren et al. 1991). Pod growth is realized by constant elongation, which starts immediately after pollination and reaches about 2 cm each day for up to 9 to 13 d. Fruit weight increases rapidly up to 9 or 10 days after pod set followed by gradual increases to 21 days. Fruits harvested more than 7 days after pod set become poor in quality due mainly to an increase in crude fiber and a gradual reduction in moisture, crude protein, and starch content. Sugar content increases up to the ninth day and declines thereafter. Changes in sugar and acidity of the pods seems to affect table quality only to a minor extent, whereas crude fiber accumulation and reduction in the moisture content have a significant influence. Baxter et al. (1987) reported a simple method for determining fibrousness in okra pods. Okra mucilage makes okra dishes unappealing to many people. The mucilage is a sticky substance of acidic polysaccharides and has viscous colloidal dispersion properties in water, which makes it appropriate for preparing soups or stews with a desired slimy consistency. Africans traditionally extracted mucilage from almost all plant parts to prepare local dishes. Extraction and characterization of various mucilages are reported by EI-Mahdy and EI-Sebaiy (1984), Tomoda et al. (1985), and Shimizu and Tomoda (1985). Ames and MacLeod (1990) have described 148 volatile compounds of okra. F. Genetics and Breeding The sensitivity of okra to several diseases and pests is a serious production problem. However, the transfer of resistance from wild relatives has been hampered by sterility problems (Nerkar and Jambhale 1985; Hamon and Yapo 1986; Fatokun 1987; Hooda and Dhankhar 1992). A. caillei and A. tetraphyllus have been utilized in the improvement of

52

E. DUZYAMAN

okra. A few viable seeds were produced in F 1 hybrids (Jambhale and Nerkar 1983a; 1985; Fatokun 1987), and through a series of backcrosses it was possible to transfer a "symptomless carrier" type of tolerance to Yellow Vine Mosaic Virus from A. cajllei (Jambhale and Nerkar 1985, 1986) and from A. tetTaphyllus (IBPGR 1991c) to the conventional okra. Crossing between promising parents combined with pedigree selection or backcrossing remains the most common breeding procedure (Corley 1985; Scott et al. 1989,1990). There is little information on improvement using biotechnology, but in vitro DNA extraction (Kochko et al. 1990) and plant regeneration from various explants and callus tissue have been reported (Mangat and Roy 1986; Roy and Mangat 1989). Recent genetic improvement has emphasized plant characteristics such as semidwarf plant stature, reduced branching, moderately lobed leaves for increasing fruit visibility to improve harvest, red ornamental pigmentation, early maturity, and smooth, dark green pods with slow fiber development (Corley 1985; Jambhale and Nerkar 1986; Scott et al. 1989,1990; Kulkarni and Nerkar 1992). A summary of the latest screening programs for resistance to some major pests and diseases are presented in Table 2.4. Okra lines resistant to root-knot nematodes, shoot and fruit borer, and leafhopper (Uthamasamy and Subramaniam 1985) have been identified. Breeding for high productivity, development of cultivars suited to specific environments, better multiplication and distribution of certified seed, and governing resistance to specific pests and diseases represents the current scope of programs in okra improvement (Seshadri and Chatterjee 1983; Koechlin 1991). Genetic variation among genotypes has been analyzed by Martin et al. (1981), Ariyo (1987b, 1990a), and Ariyo and Odulaja (1991). Diversity in fruit shape appears to be highest in West African material (Hamon and Charrier 1983; Hamon et al. 1986; Hamon et al. 1991), and along with flowering behavior (Ariyo 1987b), it accounts for most of the variation among genotypes (Martin et al. 1981; Ariyo 1990a; Koechlin 1991). The low genotypic and phenotypic variability for pod yield/plant indicates limited scope for further improvement through selection (Ariyo 1990b). Little hybrid vigor has been reported in okra, and genetic analysis of many characteristics indicates additivity (Dutta 1983; Hamon et al. 1991; Koechlin 1991) based on yield components (Dutta 1983; Agarrado and Rasco 1986), pest resistance (Veeraragavathatham and Irulappan 1990), and quality characteristics (Elangovan et al. 1983). The presence of genotype-environment interaction in numerous characteristics in okra makes it difficult to get a reliable estimation of heritability to predict the rate of genetic progress under selection. Most of the important yield components [e.g., pod yield/plant, pods/plant,

2. OKRA: BOTANY AND HORTICULTURE Table 2.4. in okra.

53

Screening of world germplasm for resistance to major pests and diseases No. of Okra Genotypes

Pathogen or Pest Root-knot nematodes Meloidogyne spp. M. javanica M. javanica and M. incognita M. javanica M. incognita Shoot and fruit borer Earias spp. Earias spp. Yellow Vein Mosaic Virus Yellow Vein Mosaic Virus Powdery mildew Erysiphe cichoracearum

Total

Resistant or Tolerant

Reference

35 29

1 resistant 2 tolerant

Jain and Bhatti 1984 Ramakrishnan 1990

140 145

None 3 resistant

Resende and Ferraz 1987 Darekar and Ranade 1990

97 1000 74 44

5 tolerant 50 tolerant 1 resistant Q 9 resistant Q

Sharma and Dhankhar 1989 Bhalla et al. 1989 Sharma and Sharma 1984 Jambhale and Nerkar 1983a

44

5 immune b

Jambhale and Nerkar 1983a

GA. manihot

bIncluding crosses among A. esculentus x A. manihot and A. esculentus x A. tetraphyllus.

branches/plant, final plant height (Ariyo 19S7a, 1990b,c; Veeraragavathatham and Irulappan 1990), flowering behavior (Ariyo 19S7a, 1990c), and seed yield (Adetunji and Chheda 19S9; Ariyo 1990b; Veeraragavathatham and Irulappan 1990)] lack stability due to strong environmental influence, suggesting the need for breeding for specific environments (Ariyo 1990b,c). The only genotypic yield component correlated with pod yield/plant were 100-seed weight, number of branches/plant, and edible pod length and weight (Gulshan and La119S6; Ariyo et al. 19S7; Ariyo 1990b). Heritability of various characteristics have been reviewed by Martin et al. (19S1) and Koechlin (1991). The genetics of some simply inherited characteristics in okra are summarized in Table 2.5. The most effective mutation rates were obtained by 40 to SO krad gamma ray seed treatments in alternative, recurrent, and single treatments. Albino and chlorina chlorophyll mutants (Jambhale and Nerkar 19S2, 19S5) and viable mutants with altered plant stature, fruits, or leaf traits were identified in the M z (Table 2.5; Jambhale and Nerkar 19S2, 19S5; Abraham 19S5). A "thick-fruit" mutant obtained by Abraham and Bhatia (1 9S4) had an average yield of 17.2 t/ha and was superior to 'Pusa Sawani' (14 t/ha) under field conditions (Abraham 19S5). A mutant with

~

Table 2.5.

Inheritance of various characteristics in okra.

Characteristic Resistance to powdery mildew

YVMva Mutations spiny fruit albino chlorina virescent dark green pale leaf short bushy subdariffa c trilobed weavy leaf drooping dwarf Pigmentation bases of petal fruit stem, pedicel, epicalyx,

Gene Action

Gene Designation

Reference

Incomplete dominant Recessive Several dominant genes Two comulementarv dominants b

Pm

Jambhale and Nerkar 1983b Uthamasamy and Subramaniam 1985 Sharma and Gill 1984 Sharma and Dhillon 1983

Incomplete dominant Recessive Single recessive Single recessive Single recessive Single recessive Single recessive Single recessive Single recessive Single recessive Single recessive Single recessive

Sf aa ch vr

dw

Jambhale and Wyatt 1985 Abraham and Abraham and Abraham and Abraham and Abraham and Abraham and Abraham and Abraham and Abraham and Abraham and

Dominant Dominant

Ppb Pf

More and Vibhute 1983 More and Vibhute 1983

Duplicate genes Recessive Single recessive

sd

More and Vibhute 1983 Wyatt 1985 Dutta 1983

dg pI sb sd trl wvl

dp

msl

aYellow Vine Mosaic Virus. bInterspecific cross between A. manihot (resistant) and susceptible cultivars of okra. cResembles Hibiscus subdariffa in its early vegetative growth.

Nerkar 1984 Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984; Bhatia 1984;

Abraham Abraham Abraham Abraham Abraham Abraham Abraham Abraham Abraham Abraham

1985 1985 1985 1985 1985 1985 1985 1985 1985 1985


55

superior freezing attributes was released as a cultivar 'Parbhani Tillu' by Kulkarni and Nerkar (1992).

III. HORTICULTURE A. Commercial Cultivars A number of attractive well-known commercial cultivars such as 'Clemson Spineless', 'Perkins Spineless', 'Velvet Round', 'Emerald', 'Cajun Queen', 'Dwarf Long Good Green', 'Red Wonder', 'Lee', 'Goldcoast', 'Louisiana' and 'Jefferson' in the United States and 'Pusa Sawani' in India have existed for more than 30 years (Siemonsma 1982a). New cultivars include 'Clemson Spineless 80', 'Cajun Delight', 'UGA Red', 'Jade', and some hybrids such as 'Annie Oakley I and II', and 'Prelude' in the United States, and 'Parbhani Kranti', 'Parbhani Tillu', and 'Arka Anamika' in India. All have performed well in a wide range of environmental conditions (Blennerhassett and EI-Zeftawi 1986; Jordan-Molero 1986; Nagel 1995) and have respectable responses to high-management cultural practices (Maynard 1987). 'UGA Red Okra', considered an edible ornamental, has red pigmentation in leaves and stems and completely red pods. It was derived by selection for high yield, semidwarf stature from the cross between 'Red Wonder' and 'Dwarf Green Long Pod' (Corley 1985). Scott et al. (1989, 1990) developed the early-maturing 'Jade' okra for fresh-market and home garden from crosses among 'Clemson Spineless', 'Emerald', 'Goldcoast', 'Louisiana 97-2-1', and 'PI248999', followed by single plant and mass selections. B. Cultural Practices 1. Plant Establishment. Ploughing or harrowing did not consistently

increase plant stands or yield in okra (Asoegwu 1987). Seedbed ridging has been used as a tillage system to increase performance (Sumner et al. 1988).

Sowing Time. In the subtropics and mild climates, okra is planted in the spring as early as possible when soil temperature is favorable (Ghanti et al. 1991; Marsh 1992). In the tropics, April-August planting is made at the onset of rains (Iremiren and Okiy 1986) to ensure vigorous plant growth, earlier flowering, and a long harvest period. To overcome low seed germination and enhance overall vegetative growth, pres owing hydration-dehydration (Enu-Kwesi et al. 1986), seed treatments with

56

E. DUZYAMAN

osmoticum (Vijayakumar et al. 1988), seed coating (Siddiqui and Alam 1988), fluid drilling (Ghate et al. 1986), or soaking seeds overnight in water before sowing (Siemonsma 1982a) are recommended. Yellowgreen or gray-green seeds that sink in water (Singh and Gill 1983) and have a moisture level of 7 to 9% (Standifer et al. 1989; Demir 1994) are preferred. A standard germination test (emergence at 18°C and 15°C in 8 h light and 16 h dark) is used to estimate seed vigor (Lotito and Quagliotti 1991).

Sowing Density. Plant density has an impact on overall plant growth and development. Plants are spaced between 4 to 16 plants/m 2 (Hermann et al. 1990), but increased density reduces almost all vegetative structures. Decreases in single plant yields are due to a decrease in percentages of nodes forming fruits (from 92.2 to 68.9%). But, due to higher density, total fruit yield per unit area remains constant (Lee et al. 1990; Gupta 1990) or even increases (Hermann et al. 1990). The small fruits preferred in Asian countries increase at high densities (Gupta 1990; Hermann et al. 1990). Dense plantings (14 plants/m 2 ) are suitable for seed production (Palanisamy and Karivaratharaju 1984). 2. Fruit Set and Harvest. Harvest is difficult and time consuming. The lack of concentrated fruit set limits mechanization possibilities. Since fruit elongation starts soon after pollination and is very rapid (ca. 2 em/d), picking must be done regularly (4 to 6 days after fruit set) to ensure good consumer quality (Perkins et al. 1952; Sistrunk et al. 1960; Tamura and Minamide 1984; Akoroda 1986b; Singh et al. 1990; Iremiren et al. 1991). This interval does not necessarily translate into harvesting every 4 to 6 days since in one harvest round the youngest fruits may not be picked and will overmature in the second round. Therefore, harvest is mostly done two, three or even four times per week. Overmature fruit need to be harvested to increase plant growth but are discarded. A simple test for fibrousness is to break the fruit tips between the fingers. Exudates from trichomes in several plant parts including pods and leaves can cause skin inflammations to field or processing workers (Matsushita et al. 1989), and harvesters often use gloves. A yield of 7 to 12 t/ha of immature fruits is considered excellent yield, but yields of 22 t/ha have been reported (Blennerhassett and EI-Zeftawi 1986; Jordan-Molero 1986; Maynard 1987; Nagel 1995). Akoroda (1986b) has estimated that dry seed yield per unit area is 90% less than fresh fruit weight. In nonhybrid cultivars, farmers can first harvest fresh fruits and then harvest seeds (Bhuibhar et al. 1989). To attain maximum seed quality, seed pods should be harvested at least 35 days after anthesis (Demir 1994), corre-


57

sponding to two to three sutures split in dehiscent cultivars (Kanwar and Saimbhi 19S7). 3. Storage. Fresh okra pods have a short postharvest life and are prone to physical breakdown such as microbial decay, shriveling, toughening, and chlorophyll degradation (Baxter and Waters 1990a), and physiological changes such as loss of sugar, soluble proteins, amino acids, and citric, malic, and ascorbic acids (Baxter and Waters 1990b). In air-stored pods, considerable deterioration in quality occurs even after two days (Tamura and Minamide 19S4). Furthermore, pods are sensitive to chilling injury, and calyx discoloration, seed browning, and surface pitting occur after three days of storage at 1 or 6°C (Tamura and Minamide 19S4; Kozukue et al. 19S4). Pods, stored under controlled atmosphere at 5% O 2 and 10% CO 2 at 1PC, and 90 to 93% humidity remained saleable after 12 days (Tamura and Minamide 19S4; Lougheed 19S7; Baxter and Waters 1990a,b). 4. Plant Nutrition. A total of 75 to 100 or up to 120 kg/ha N, 20 to 30 or

up to 60 kg/ha P, plus 60 to 130 kg/ha K is sufficient for both fruit or seed production (Majanbu et al. 19S6; Sarnaik et al. 19S6; Lee et al. 1990). Nitrogen leaching due to excessive rains (McLaurin et al. 19S4) or nonavailability due to low soil moisture (Majanbu et al. 19S6) are the reasons for the ineffectiveness of nitrogen fertilizers to improve yield (Adejonwo et al. 19S9). Excess N fertilizations can reduce yield by enhancing vegetative growth at the expense of fruit development (Majanbu et al. 19S5; Lee et al. 1990). Phosphorus should placed at 10 or 15 cm depth below the seed in two bands on either side of the seed furrow (Shivananda and Iyengar 1990). Where deficient, copper can be applied to foliage at 0.2% at 20 days and again at 40 days after sowing (Hazra et al. 19S7). Type and occurrence time of deficiency symptoms of major and minor elements in okra are described by Velho et al. (19SS). 5. Irrigation. Okra displays a "root osmotic" adjustment to water-deficit stress and tolerates water stress well (Wullschleger and Oosterhuis 1991). Nevertheless, water is the most limiting factor in okra production in areas with dry growing periods (Hamon and Hamon 1991). The effects of moisture stress depend on the phenological stage of the plant. The flowering/pod-filling stages are critical and water stress can reduce yield more than 70% (Mbagwu and Adesipe 19S7). Total water (irrigation + rain) of 460 mm during a 4-month growing period is required for good yields (Siemonsma 19S2a; Singh 19S7; Gupta 1990). A point source sprinkler system may also be used (Fapohunda 1992). However, if seed

E. DUZYAMAN

58

production is envisaged, this should be discontinued after flower induction since seeds require hot, dry weather during ripening (Singh et al. 1988; Adetunji and Chheda 1989). 6. Growth Regulator Treatments. Growth regulator treatments have been reported to enhance vegetative growth and to improve early and total yield. A single foliage spraying with chlormequat (CCC) at 1000 mg/liter or 1,1-dimethyl-piperidinium chloride (Pix) at 250 mg/liter increased early and total yield by reducing number of days to flowering and increasing the number of pods/plant (Zayed et al. 1985). Higher doses of Cycoeel (500 ppm) reduced expression of Yellow Vein Mosaic Virus (Arora et al. 1990). Daminozide, and ethephon at several doses were ineffective in enhancing growth or yield (Marsh et al. 1990). 7. Weed Control. Competition of weeds can be especially serious when okra is at the stage of establishment, with yield losses ranging from 54 to 91 % (Iremiren 1988). In developing countries such as Nigeria and Turkey, hand weeding is practiced almost exclusively. A comprehensive list of problems, costs, weed-control techniques, and critical weed interference periods in okra is discussed by Usoroh (1989). Presowing or preemergence herbicide treatments in combination with supplementary hoeing will probably give the most satisfactory result (Table 2.6). Tiwari et al. (1985), Iremiren (1988), and Adejonwo et al. (1991) obtained similar results with preemergence herbicide treatment combined with a well-timed single hoeing (4 weeks after sowing) or up to three hoeings without prior herbicide treatment. Alachlor (at 3 kg), flurochloridone (at 0.75 kg), and diphenamid (at 3.5 kg/hal significantly reduced yield (Americanos and Vouzounis 1991). The weedy okra has the potential for persistent weed problem because of the high percentage of hard seeds overwintering and germinating the following spring (Egley and Elmore 1987). Table 2.6.

Herbicides recommended for okra.

Chemical

Application Rate (kg/ha)

Reference

Alachlor Benthiocarb [thiobencarb] Fluchloralin Metolachlor + Prometryne Nitrofen Oxyfluorfen

1.5 2.0 1.0 2.0 + 1.0 2.0 0.35

Leela 1989 Tiwari et al. 1985 Tiwari et al. 1985 Adejonwo et al. 1991 Tiwari et al. 1985 Tiwari et al. 1985


59

8. Pests and Diseases. Okra can tolerate considerable apical pest damage

and at least 25% leaf damage, especially at early growth stages, before significant yield loss (Olasantan 1986,1988). Root-knot nematodes, Meloidogyne incognita (Kofoid and White) M. javanica (Treub.) and Rotylenchulus reniformis (Linford and Oliveira) are destructive (Siemonsma 1982a). Young plants are susceptible to attack (Sinhababu and Sukul 1983). Infected plants show reduced growth due to decreased water absorption capacity of roots (Sharma and Trivedi 1991). Biological nematode control has been recommended with nematicidal plant extracts of Anthocephalus cadamba (Basu and Sukul 1983), Manihot esculenta extract (DaPonte and DaPonte 1988), neem oil, karanj oilcake from Pongamia glabra (Reddy and Khan 1991), animal manures (Montasser 1991), Pasteuria penetrans in combination with soil fungi (Paecilomyces lilacinus or Talaromyces flavus) , or bacterium (Bacillus subtilis) (Zaki and Maqbool 1991). Carbofuran at 1 kg/ha or aldicarb at 0.5 to 1.0 kg/ha have been proposed (Verma and Gupta 1987). Extreme pH levels such as 5 or 10 reduced nematode incidence on okra (Jonathan and Vadivelu 1990). Trap plants have been tested by Patel et al. (1991) and pink and white periwinkle (Catharanthus roseus) reduced nematode population on okra by 100 and 95%, respectively. Leafhoppers [Amrasca devastans (Dist.) and jassids [A. biguttula biguttula (Shir.)] cause serious damage in okra by heavy desapping of leaves leading to phytotoxemia, known as hopperburn. The insecticides tested in Table 2.7 were persistent and controlled either pest population for about 15 days. Resistance of okra to leafhopper feeding is present in some lines (Uthamasamy 1985a; Singh and Agarwal 1988), enhanced by the presence of long lamina hair (Uthamasamy 1985b). Lal et al. (1990) observed that adverse climatic conditions, especially continuous heavy rainfall, high relative humidity, low mean temperature, and low light, have a negative impact on leafhopper population on okras. Okra itself has been investigated as a trap plant and displayed promise when intercropped with greenhouse eggplants (Bernardo and Taylo 1990). The shoot and fruit borer, Earias vittella (Fab.), also known as the potted ball worm in cotton fields, is one of the most ubiquitous pests, causing damage to okra fruits and shoots to the extent of 90%. The shoot and fruit borer develops and pupates mostly on fruit (67%) followed by seeds (60%), pericarp (28%), and axil (10%) (Singh and Singh 1987). Weekly applications of fenvalerate (0.1 kg/hal or monocrotophos (0.05%) (Mohan and Jagan-Mohan 1985) are recommended for use in an integrated control scheme. Mortality rates of mites [Tetranychus macfarlanei (Baker & Pritchard)] in okra vary between 57 and 72% for the acaricides tested by Patel and

E. DUZYAMAN

60 Table 2.7.

Insecticides for the control of the leafhoppers in okra.

Insecticides

Concentration (%)

Reference

Cypermethrin Fenvalerate

0.006-0.008 0.006-0.008

Flucythrinate Deltamethrin Endosulfan Carbaryl

0.006 0.002

Kakar and Dogra 1988; Dahiya et al. 1990 Mohan and Jagan-Mohan 1985; Kakar and Dogra 1988; Dahiya et al. 1990 Dahiya et al. 1990 Kakar and Dogra 1988; Dahiya et al. 1990 Yadav et al. 1988; Dahiya et al. 1990 Mohan and Jagan-Mohan 1985; Yadav etal.1988 Yadav et al. 1988 Mohan and Jagan-Mohan 1985; Kakar and Dogra 1988

Oxydemeton-methyl b Permethrin

0.05-0.07°

0.15 0.025°

0.008

°Including jassids [A. biguttula biguttula (Shir.)]. bShould be discontinued after flower bud formation.

Yadava (1988) and Chawla et al. (1988) (Table 2.8). The longest protection duration was achieved with UC-55248 and dicofol with effectiveness for 15 days after treatment. Methomyl or profenofos (0.5 kg/hal are recommended against aphids [Aphis gossypii (Glover)] (Mohan and Jagan-Mohan 1985). In Asia, the Yellow Vine Mosaic Virus (YVMV) transmitted by the whitefly, Bemisia tabaci (Genn.), is a limiting factor in okra production. In Africa, the Okra Mosaic Virus (OMV) , transmitted by the flee beetles of the genus Podagrica, is widespread but less important than Okra Leaf Curl Virus (OLCV), transmitted by the whitefly, Bemisia tabaci (Genn.). These viruses can reduce fruit yield by 30 to 70%.

Table 2.8.

The control of mites in okra. Miticide

Concentration (%)

Sevisulf (carbaryl + sulphur) UC-55248°

0.1 0.2

Dicofol Sulphur Ethion Phosalone Methamidophos Phosphamidon

0.05 0.8 0.05 0.06 0.05 0.03

Reference Patel and Yadava 1988 Patel and Yadava 1988; Chawla et al. 1988 Patel and Yadava 1988 Patel and Yadava 1988 Chawla et al. 1988 Chawla et al. 1988 Chawla et al. 1988 Chawla et al. 1988

0[5,5-dimethyl-2-(2-methylphenyl)-3-oxo-l-cyclohexen-l-yl-2-ethylhexanoate].

61


Certain vegetables common around okra plantings, such as eggplant, are very susceptible to whitefly and make control difficult (Mohanty and Basu 1990). Control of the vector with insecticides (Table 2.9), combined with regular removal of virus-infected plants, is suggested (Sinha and Chakrabarti 1982). Some okra lines have been identified by Atiri (1990) where YVMV symptoms appear only after the commencement of fruiting, leaving insufficient time for the disease to significantly reduce yield and avoiding expensive control measures against the whitefly vector. The major soil-born fungi in growers' fields are Fusarium spp., Verticillium spp., Rhizoctonia spp., Macrophomina spp., and pythium spp. Due to its deep root structure, okra does not respond well to soil fungicides, but application of metham-sodium in 2.5 em of water was effective in controlling Rhizoctonia solani (Kuhn.) and Pythium spp. (Sumner and Phatak 1988). Seed-borne fungal flora of okra include Aspergillus spp., Cochliobolus lunatus, Fusarium spp., and Rhizoctonia solani (Kuhn.) which can produce varying degrees of seed and seedling mortalities (Gupta Kumkum et al. 1989). No single fungicide (Chlorothalonil, Triflumizole, Thiram, Carbendazim or Flutolanil) was effective for control of seed-borne fungi but combinations of all five test fungicides enhanced seed germination, growth, and vigor (Hema et al. 1991). Periodical fumigation programs with an ammonia concentration of 5 ppm are beneficial in seed storehouses (Tyagi 1986). To control powdery mildew [Erysiphe cichoracearum (DC.)], one spray of carbendazim (2%) or tridemorph (0.08%) in combination with two dustings of sulphur every 10 to 15 days have been recommended, but fungicide application under humid conditions is ineffective (Gawande and Peshney 1987).

Table 2.9. Control of the Yellow Vine Mosaic Virus (YVMV) and Okra Leaf Curl Virus (OLCV) by applications against the whitefly vector [Bemisia tabaci (Genn.)]. Insecticide

Concentration (%)

Dimethoate Endosulfan Phosphamidon Methyl demeton G Foratox [phorate]

0.06%/fortnightly 0.07%/fortnightly 0.02%/3 sprays 0.025%/3 sprays 15 kg/ha single b

GDemeton-S-methyl bSoil application

Reference Sinha Sinha Singh Singh Singh

and Chakrabarti 1982 and Chakrabarti 1982 et a1. 1989 et al. 1989 et al. 1989

62

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C. Processing 1. Canning and Freezing. The rapid expansion of okra processing by

freezing and canning in the last three decades has been responsible for the increase of commercial okra production, as well as the development of suitable cultivars such as 'Louisiana Green Velvet' (Woodroof and Shelor 1958). The ideal pod type for freezing is short, dark green, and round or multifaceted (Sistrunk et al. 1960). Canned okra requires color retention (chlorophyll content), low mucilage content, and low fiber content (Woodroof and Shelor 1958). Pod texture should be firm so that broken tissue or seeds are not present in the liquor, for which adequate nitrogen application (135 kg/ha) prior to planting is essential (McLaurin et al. 1984). 2. Drying. Sun drying of pods is often carried out in developing countries for consumption in the off season. The usual process is to leave whole or sliced pods in the sun for 7 to 10 days to reduce moisture content to 5%. There are only small differences in fat, protein, carbohydrate, and mineral content between fresh and dried samples, but dried samples show considerable loss of vitamins, particularly vitamin C and riboflavin (Okoh 1984). Drying has increased in Africa and Asia. Predrying treatments by sulphating and salting maintained 92% mucilage and 72% color retention (Echetama 1991). Solar dryers have been tested or used for dehydrating whole or sliced okra pods (Echetama 1991; EI-Shiatry et al. 1991).

IV. RESEARCH NEEDS Many of the limitations in okra production can be overcome by advances in genetic improvement. Genetic resistance is greatly needed in many parts of the world because okra is extremely sensitive to a large number of pests and diseases. Resistance to area-specific viruses, such as the Yellow Vine Mosaic Virus in Asia and Okra Mosaic Virus in Africa; soilborn fungi, such as Fusarium spp. and Verticillium spp.; and root-knot nematodes may be the first priority of breeders throughout the world. Biotechnological techniques could have practical relevance in okra. Progress in breeding would be facilitated by increased germplasm exchange. The publication of world germplasm collections would greatly facilitate the use of exotic germplasm. Techniques to overcome intraspecific barriers would expand the available gene pool. In this connection, research on in vitro technology such as embryo rescue tech-

2. OKRA: BOTANY AND HORTICDLTDRE

63

niques needs to be explored in okra. Furthermore, the addition of photoperiod insensitivity to A. caillei would allow further exploration in this species by itself or by introgression into A. esculentus.

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Ariyo, O. J. 1993. Genetic diversity in West African okra (Abelmoschus caillei) (A. Chev.) Stevels-Multivariate analysis of morphhological and agronomical characteristics. Gen. Resources Crop EvoI. 40:25-32. Ariyo, O. J., and A. Odulaja. 1991. Numerical analysis of variation among accessions of okra (Abelmoschus esculentus (1.) Moench), Malvaceae. Ann. Bot. 67:527-531. Ariyo, O. J., M. K Aken'Ova, and C. A. Fatokun. 1987. Plant character correlations and path analysis of pod yield in okra (Abelmoschus esculentus). Euphytica 36:677-686. Arora, S. K., B. S. Dhankar, and N. K. Sharma. 1990. Effect of Cycocel and NAA on vegetative growth, flowering, fruit-set and incidence of YVM of okra. Res. Dev. Rep. 7:123-129. Asoegwu, S. N. 1987. Comparison of tillage systems for the production of egusi-melon (Colocynthis citrullus 1.) and okra (Abelmoschus esculentus 1. Moench) in Eastern Nigeria. Crop Res. 27:77-90. Atiri, G. 1. 1990. Relationships between growth stages, leaf curl symptom development and fruit yield in okra. Scientia Hort. 45:49-53. Babu, K. V. S., and O. P. Dutta. 1990. Pollen fertility studies in Abelmoschus spp. South Indian Hort. 38:109. Basu, S. P. S., and N. C. SukuI. 1983. Effect of root-knot nematode Meloidogyne incognita on the total protein, carbodydrate and lipid in roots at different growth stages of Hibiscus esculentus. Indian J. NematoI. 13:66-70. Bates, D. M. 1968. Notes on the cultivated Malvaceae. 2. Abelmoschus. Baileya 3:99-112. Baxter, 1., and L. Waters, Jr. 1990a. Controlled atmosphere effects on physical changes and ethylene evolution in harvested okra. HortScience 25:92-95. Baxter, L., and 1. Waters, Jr. 1990b. Chemical changes in okra stored in air and controlled atmosphere. J. Am. Soc. Hort. Sci. 115:452-454. Baxter, 1., L. Waters, Jr., and W. Breene. 1987. A quick method for determining fibrousness of vegetable tissue. HortScience 22:315. Bernardo, K N., and L. D. Taylo. 1990. Preference ofthe cotton leafhopper, Amrasca biguttula (Ishida) for okra, Abelmoschus esculentus (Linn.), and eggplant, Solanum melongena Linn. Philippine Agr. 73:165-177. Bettencourt, K, and J. Konopka. 1990. Directory of germplasm collections. 4. Vegetables. IBPGR, Rome. Bhalla, S., B. R Verma, and T. A. Thomas. 1989. Screening of okra germplasm for field resistance to fruit-borer, Earias spp. Indian J. EntomoI. 51:224-225. Bhat, R B., J. A. Inamdar, and D. J. Weber. 1988. Leaf architecture of some Malvaceae. Angewandte Botanik 62:135-146. Bhuibhar, B. R, K. G. Mahakal, P. B. Kale, and S. G. Wankhade. 1989. Effect oftime of sowing and number of pickings of green fruits on growth and seed yield of okra (Abelmoschus esculentus (L.) Moench). PKV Res. J. 13:39-43. Bisht,1. S., R K. Mahajan, and R S. Rana. 1995. Genetic diversity in South Asian okra (Abelmoschus esculentus) germplasm collection. Ann. AppI. BioI. 126:539-550. Blennerhassett, R M., and B. M. El-Zeftawi. 1986. Productivity and growth of six okra cultivars. Australian J. Expt. Agr. 26:625-629. Bryant,1. A., J. Montecalvo Jr., K. S. Morey, and B. Loy. 1988. Processing, functional, and nutritrional properties of okra seed products. J. Food Sci. 53:810-816, 856. Candlish, J. K., L. Gourley, and H. P. Lee. 1987. Dietary fiber and starch contents of some Southeast Asian vegetables. J. Agr. Food Chern. 35:319-321. Charrier, A. 1984. Genetic resources of the genus Abelmoschus Med. (okra). (English translation). IBPGR, Rome.


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Charrier, A., and S. Hamon. 1991. Germplasm collection, conservation and utilization activities of the Office de la Recherche Scientifique et Technique d'Outre-Mer (ORSTOM). p. 41-52. In: N. Q. Ng, P. Perrino, F. Attere, and H. Zedan (eds.), Crop genetic resources of Africa, vol. II. lITA, Ibadan. Chawla, V. K, A V. Thakar, and C. P. S. Yadava. 1988. Bioefficiency of some insecticides and acaricides against red spider mite, Tetranychus macfarlanei Baker and Pritchard feeding on okra. Indian J. Entomol. 50:123-125. Chevalier, A, 1940. L'origine, la culture et les usages de cinq Hibiscus de la secion Abelmoschus. Rev. Bot. Appl. 20:319-328,402-419. Corley, W. 1. 1985. UCA red okra: a new edible ornamental. Res. Report, Agr. Expt. Sta., Univ. Georgia: 484. Dahiya, AS., S. S. Sharma, A. N. Verma, and S. Ombir. 1990. Comparative efficacy of different insecticides against jassid, Amrasca biguttula biguttula (Ishida) on okra. J. Insect Sci. 3:83-87. Damania, A B. 1985. Collecting in Mauritius. Plant Genetic Resources Newslett. 63:43-46. DaPonte, J. J., and J. J. DaPonte. 1988. "Cassareep": an unconventional nematicide. Cassava Newslett. 12:9. Darekar, K S., and M. S. Ranade, 1990. Resistance of some okra, Abelmoschus esculentus, cultivars to root-knot nematode, Meloidogyne incognita. Int. Nematol. Network Newslett. 7:6-7. Demir,1. 1994. Development of seed quality during seed development in okra. Acta Hort. 362:125-131.

Dutta, O. M. 1983. Male sterility in okra (Abelmoschus esculentus (1.) Moench.) and bottle gourd (Lagenaria siceraria (Mol.) Standl.) and its utilization in hybrid seed production. Thesis Abstracts 9:341-342. Univ. Agr. Sci. Bangalore. Echetama, J. K 1991. Development of sun-dried okra product (using a see-saw solar drier). Tech. Bul. National Hort. Res. Inst., Ibadan 15:16. Egley, G. H., and C. D. Elmore. 1987. Germination and the potential persistence of weedy and domestic okra (Abelmoschus esculentus) seeds. Weed Sci. 35:45-51. Elangovan, M., C. R Muthukrishnan, and 1. lrulappan. 1983. Evaluation ofbhendi hybrids and their parents for crude fibre content. South Indian Hort. 31:241-243. El-Mahdy, A R, and 1. A EI-Sebaiy. 1984. Preliminary studies on the mucilages extracted from okra fruits, taro tubers, Jew's mellow leaves and fenugreek seeds. Food Chern. 14:237-249.

El-Shiatry, M. A, J. Muller, and W. Muhlbauer. 1991. Drying fruits and vegetables with solar energy in Egypt. Agr. Mechanization Asia, Africa, Latin America 22:61-64. Engels, J., and T. Dadi. 1986. Germplasm exploration in Gambela: local okra and cowpea. PGRC/E.ILCA Germplasm Newslett. 11:15-19. Enu-Kwesi, L., M. Nwalozie, and D. 1. Anyanwu. 1986. Effect of pre-sowing "hydrationdehydration" on germination, vegetative growth and fruit yield of Abelmoschus esculentus grown under two soil moisture regimes. Trop. Agr. 63:181-184. Fapohunda, H. O. 1992. Irrigation frequency and amount for okra and tomato using a point source sprinkler system. Scientia Hort. 49:25-31. Fasheun, A 1988. Soil temperature management for optimal seedling emergence in A. esculentus and C. olitorius. Int. Agrophysics. 4:333-338. Fatokun, C. A. 1987. Wide hybridization in okra. Theor. Appl. Gen. 74:483-486. Gawande, P. S. and N. 1. Peshney. 1987. Seasonal incidence and chemical control of powdery mildew of bhendi (Abelmoschus esculentus 1.) in Vidarbha. PKV Res. J. 11:54-57.

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Sweet Sorghum E. 1. Hunter and 1. C. Anderson Department of Agronomy Iowa State University Ames, Iowa 50011

I. Introduction II. Botany A. Taxonomy B. Origin and Distribution C. Morphology and Anatomy D. Chemical Composition III. Crop Physiology IV. Genetic Improvement V. Syrup Production A. Sweet Sorghum Culture B. Harvesting and Processing C. Marketing and Distribution VI. Future Prospects Literature Cited

I. INTRODUCTION

Sorghum bicolor consists of a mixture of types that range from grain types with relatively low sugar concentrations in juice of the stalk at grain maturity to sweet-stalked types called sweet sorghums that have 10 to 25% sugar in stalk juice near the time of grain maturity. Sweet sorghums are mainly used for producing sorghum syrup. Sorghum syrup has a taste and other characteristics that differ from sugar cane molasses and from corn syrup made from hydrolyzed starch of maize grain, which is primarily glucose. Sorghum syrup consists of mixture of glucose, fructose, and sucrose along with many other impurities in the juice expressed from stalks of sweet sorghum. Sweet sorghum has been grown Horticultural Reviews, Volume 21, Edited by Jules Janick ISBN 0-471-18907-3 © 1997 John Wiley & Sons, Inc. 73

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as a specialty crop in most of the United States, with the greatest popularity and tradition in the southeast, mid-South, and lower Midwest. The greatest sorghum syrup yield per unit of land occurs at the late milk stage of grain development, before grain maturity. If stalks are cut later, stalk sugar may be used for grain growth and, at the end of the season, cool temperatures reduce photosynthesis in this crop of tropical origin. There are some cultures that allow sweet sorghum to mature the grain before harvest. For example, in India the seed of the plant may be used as animal feed, as a food, or fermented to a beer. The expressed stalk juices are evaporated to sorghum syrup, fermented to ethanol that is distilled with solar energy to make a fuel, and finally the pressed stalks are fed to cattle (National Academy of Science 1996). With the onset of several energy crises in the United States, sweet sorghum has received attention as a source ofbiofuels. A mixture of 10 to 15% ethanol with gasoline is an excellent replacement for tetraethyl lead in gasoline. Maize grain, a renewable source of energy that is storable, transportable, and available, developed as the source of ethanol for oxygenating gasoline. The U.S. DepartmentofEnergy has subcontracted a number of studies to evaluate herbaceous crops for energy. For much of the United States, the most promising herbaceous crops are switchgrass and sweet sorghum. Sweet sorghum cultivars have proven exceptionally adaptive to a wide range of environments for a grass of tropical origin (Smith et al. 1987). Sugar in a crop of sweet sorghum has the potential to produce up to 8,000 liters of ethanol per hectare or about twice that of maize. Sweet sorghum as a source of ethanol has not been developed because it is bulky and heavy and also spoils unless processed immediately after harvest. The authors along with others are studying methods to overcome these problems. In Brazil, sugarcane (Saccharum officinarum) is mainly used for ethanol production, but increasing amounts of sweet sorghum are being used. The length of the growing season for sweet sorghum is about half of that for sugarcane, and its culture from seed establishment is simpler and less expensive than that for sugarcane. In this chapter, we emphasize the taxonomy, origin, distribution, physiology, production, and processing of sweet sorghum. II. BOTANY

A. Taxonomy

The tribe Andropogonae includes many of the tall grass genera Miscanthus and Andropogon, as well as Tripsaaum, Zea, Saccharum, Sorgastrum, and Sorghum. Sorghum may be more closely related to Sorgastrum

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than to Saccharum (sugarcane). Extensive classification of Sorghum by Snowden (1936) resulted in 48 cultivated and related taxa, but this complex group was condensed by Harlan and deWet (1972). The genus is subdivided into four sections (Para-sorghum, Chaetosorghum, Striposorgum, and Sorghum). A partial taxonomy of section Sorghum is presented in Table 3.1. In S. bicolor (L.) Moench, the cultivated sorghums are in subspecies bicolor and the spontaneous races are in subspecies verticilliflorum. Harlan and deWet in 1972 classified subspecies bicolorinto five races (Bicolor, Caudatum, Durra, Guina, and Kaffir) with most of the sweetstalked sorghums (sweet sorghum) in subrace Sorgo of race Bicolor. The section Sorghum has one polymorphic population of (2n = 2x = 20) in tropical Africa now known as subspecies verticulliflorum and another distinctly different population in Southeast Asia known as S. propinquum. Hybrids between the two populations are fertile but they are separated as distinct species because of distributional and morphological differences. The tetraploid S. halepense (2n = 4x = 40) occupies a continuous area between subspecies verticilliflorum and propinquum. It probably came from chromosome doubling of a natural cross between these two (Dogget and Prosada Rao 1995). The base chromosome number may be five as it is in some of the other sections of the Sorghum genus. The origin of the cultivated crop is within the section Sorghum

Table 3.1. Partial taxonomy of the section Sorghum of the Sorghum genus associated with origin of sweet sorghum. Species

Subspecies

S. halepense

Race Halepense

Subrace Halepense Johnson grass Almum

Miliaceum Controversum S. propinquum S. bicolor

drumnondii verticilliflorum

bicolor

Verticilliflorum Arundinaceum Virgatum Aethiopicum Bicolor Caudatum Durra Guina Kafir

Sorgo Sudangrass Hegari Durra-bicolor

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E. 1. HUNTER AND I. C. ANDERSON

from the wild subspecies verticilliflorum of tropical Africa with introgression from S. propinquum and S. halepense. The Bicolor race exhibits the most morphological variation of the five races, yet it is presently the least cultivated (Harlan 1975). It may have originated from the wild race Aethiopicum (deWet and Harlan 1971) which is a widely distributed type, often growing in massive stands in central Africa. The Bicolor race is typified by long, hard, clasping glumes; elongate seed shape; long, stiff awns; and an open inflorescence. In some cultivars, the glumes remain with the grain (Martin 1970). These characteristics are usually associated with primitive cultivars (Harlan and deWet 1972). They resemble the weedy sorghums but lack a natural dispersal mechanism. When they occur away from their center of origin, members of the Bicolor race are either relics of ancient domesticated populations or recent derivatives of hybridization events between cultivated races and wild types (deWet 1978). Bicolor cultivars are likely to be reproduced wherever wild and cultivated sorghums grow together (Harlan and deWet 1972). In other sweet-stalked sorghums, the sweet characteristic probably has been introduced from race Bicolor. For ex~mple, there are important Dura-Bicolor intermediates in the Ethiopian highlands (Harlan and deWet 1972). Other sweet-stalked cuItivars belong to the Kafir race (Martin 1970). Race Kafir is predominantly grown in Tanzania and regions to the south. Its distribution and morphology suggest race Verticilliflorum (a wild grass common to the African savanna) as the ancestor of Kafir (deWet and Huckabay 1967). This race is characterized by small, exposed, fairly symmetrical grains and compact to semicompact panicles, often cylindrical in shape. Glumes tightly clasp the longer grain. In general, Kafir has been important in the breeding of intermediate types (Harlan and deWet 1972). Traits from other races have been incorporated in sweet sorghum cultivars to improve characteristics such as seed size for harvestability. Hegari, a subrace of the Caudatum race, is often associated with the Sorgos. Caudatum intermediates are in general very important as a source of yielding ability and high-quality grain (Harlan and deWet 1972). Caudatum intermediates are characterized by "turtle-backed" grains that are flat or concave on the side next to the first glume and convexly curved on the other, with the grains exposed between shorter glumes (deWet 1978). Also, introgression of wild types and old cultivars for improving resistances has introduced new grain characteristics and general morphologies. Therefore, sweet sorghum cultivars display a wide variety of seed types and panicle shapes.

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Classification of the sorghums is made difficult due to the diversity generated by hybridization and recombination (Bunting 1990). Some sorghums are self-pollinated and others show up to 50% outcrossing (Gill and Year 1980). Sorghum sudanese, or sudangrass, is derived from a hybrid swarm of Bicolor race material and a weedy form of the Virgatum race and is more properly classified as a subrace of the Bicolor race, as we show in Table 3.1, instead of as a separate species. It is commonly used as a forage or in crosses with sweet or grain sorghum (Harlan and deWet 1972). The cultivated sorghums all have 10 chromosomes (x = 10). Harlan and deWet (1971) suggest using a gene pool classification system with respect to the subspecies level of variation. In this system, the primary gene pool includes all the races that can be crossed with the crop of interest, yielding fertile hybrids with viable offspring. The primary gene pool for cultivated S. bicolor subsp. bicolor includes all of the cultivated and spontaneous subspecies, both wild and weedy types. The secondary gene pool includes the taxa that can be crossed with the crop, but exhibit restricted gene flow due to many reproductive barriers. Sorghum halapense, a perennial sorghum, would be in the secondary gene pool for S. bicolor. Finally, the tertiary gene pool includes all those species that can be crossed with the crop, but the hybrids are lethal, sterile, or anomalous. For example, S. bicolor is tertiarily related to maize and sugarcane (Harlan and deWet 1971). There may have been an ancient ancestor to S. vericolor (section ParaSorghum), S. bicolor, and S. halapense. This could have been a species with a base chromosome number of five that then differentiated into at least three groups: species with large chromosomes (Para-Sorghum), species with medium-sized chromosomes (Stiposorghum), and species with small chromosomes (Sorghum), which includes all the cultivated sorghums (Dube et al. 1991). The five races of S. bicolor subsp. bicolor maintain their distinct morphologies through ethnological and spacial isolation (deWet 1978).

B. Origin and Distribution The wide distribution and immense amount of morphological variability in Sorghum bicolor suggest an ancient origin. Although it is truly a "noncentric" crop, archeological evidence supports an African center of origin and domestication (deWet and Harlan 1971). All of the general types of sorghum found in other parts of the world are also found in Africa. The most diverse representation of sorghum types is found in east central Africa (Damon 1962). In Africa, stands of wild sorghum extend

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across the savanna, from South Africa to Ethiopia and westward to Mauritania and are often used as a food source in times of famine (deWet and Harlan 1971). As the continent's peoples made the transition to agrarian societies, the highly transient nomadic groups aided in creating an abundance in species types through seed trade and improvement (Bunting 1990). New hybrid combinations were produced almost continuously as geographically isolated sorghum populations, both wild and cultivated, were brought together through human migrations (deWet and Huckabay 1967). Sweet sorghum first arrived in the United States in association with African slave trade in the 17th and 18th centuries. Additional types arrived as heirlooms with European immigrant groups and through collection trips to Africa in the mid-1800s. Sweet sorghum from Africa also evolved into new cultivars in China and Japan that now typify those areas (Martin 1970). Sweet sorghum culture in the United States expanded after the introduction of the cultivar 'Chinese Amber,' via France in 1853. Fifteen additional cultivars were brought by Leonard Wray from Africa in 1854. These added greatly to the foundation of sweet sorghum production in the United States as they were used as parents to produce other popular cultivars (Coleman 1970). Eventually, improved sorghum cultivars were exported by the United States to South America and Australia (Martin 1970). Due to the extensive amount of variability available, collections are still being made in Africa and Asia in the ongoing search for new desirable traits. This is part of a larger movement toward preserving and updating global germplasm collections. Production of table syrup from sweet sorghum increased and peaked at over 36 million liters in 1946 (Coleman 1970). During World War II, sugar was rationed and many farm families grew small areas of sweet sorghum. The leaves and heads were stripped from the plants before transporting the stalks to a person who had a press and evaporation pans for making sorghum syrup. For these families, sorghum syrup became the main sweetener for baking and as a spread on bread and biscuits. Sorghum syrup did not replace corn syrup used with milk from cows for baby formula, probably because of the taste and impurities in sorghum syrup. With the end of the war, corn syrup and sugarcane molasses regained dominance over sorghum syrup. Sweet sorghum production declined steadily into the 1970s with the onset of low cane sugar prices (Kuepper 1992). However, throughout all rural areas in the United States where sweet sorghum can be grown, there are a few people with small presses who make sorghum syrup and a few larger operators who commercially produce sorghum syrup on a regional basis.

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Morphology and Anatomy

The Andropogoneae are all C4 plants and are mostly tropical or warm temperate, especially associated with savanna climate. Although one of the most morphologically complex tribes in terms of inflorescences, it is generally considered to be monophyletic. The tribe is characterized by paired spikelets, usually with one sessile and one pedicellate. The sessile spikelet is fertile and the pedicellate imperfect (pollen only) and often deciduous (Martin 1970). The pedicellate spikelet is reduced. The spikelets have two glumes varying from hard to papery, a membranous and sometimes awned lemma, and a reduced membranous palea. The paired spikelets usually disarticulate as a unit below the glumes and with part of the rachis (Gould and Shaw 1983). The spikelets are more or less terete or dorsally compressed with a two-keeled first glume. The inflorescence is made up of units called racemes or rames, a series of paired spikelets. In sorghum, the terminal inflorescence is a panicle. Modifications in the sorghum inflorescence have involved a general multiplication and condensation of spikelets and branches, as is seen in the domestication of many grasses (Harlan et al. 1973). Leaf anatomy in this tribe is conservative without highly specialized anatomical features. The leaf surface is highly variable and may be related to environments and therefore distribution. Most of the diversity of the tribe is in the Old World, especially Asia and Africa. In the generalized sorghum panicle, the primary branches bear short, dense, rames with few spikelet pairs per rame. Branches terminate in three spikelets, one sessile and fertile and two pedicelate and imperfect (Gould and Shaw 1983). The internodes of the rachis are pubescent. The overall shape can be upright, recurved, or inclined especially in heavy panicles on long pedicels (Martin 1970). The panicle shape ranges from cylindrical to ellipsoidal and may be dense and compact or open and loose. This is determined by the length and number of branches as well as the number of panicle internodes (Martin 1970). Glumes vary widely in color, size, and texture. Grain size and color vary similarly (Martin 1970).

The number of internodes produced in sweet sorghum is determined by four maturity genes controlled by photoperiod and temperature interactions (Quinby 1967). Internode length is determined by four major genetic factors as well as environmental parameters. Stalk thickness increases with the number of internodes produced; often, late-maturing cultivars have thicker stems than early cultivars (Martin 1970). The size of the panicle and the peduncle are often independent.

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The sweet sorghums tend to produce more tillers than other sorghum types; some have the potential to produce 8 to 10 tillers and as few as 1. Hybrid sorghum tends to tiller more than the inbred lines. In cultivars with race Kafir and race Dura characteristics, fewer tillers are produced (Sielinger and Martin 1939). Branching at upper internodes as well as the production of tillers increases as the space between plants increases. The number of leaves produced in sorghum cultivars depends on the length of the vegetative period. Typically, there are 8 to 10 nodes below the soil surface that elongate very little and the total number produced ranges from 15 to 40. Leaf blades are long and flat with width varying from narrow to broad. The ligule is membranous, with or without a fringe of hairs (Gould and Shaw 1983). The leaf midrib often appears cloudy in sweet sorghum cultivars. There is much variation in foliar colors, spotting, and streaking. Leaf angle also is affected by spacing or plant population. Leaf angle becomes more erectophylic with an increase in population. Leaf width has been shown to be reduced as well. These responses to light involve development of a leaf canopy with the most efficient exposure to incident solar radiation. Therefore, differences in yield between erect and planophylic leaf architectures are minimal (Clegg 1972). Little information is available on sweet sorghum stalk anatomy. Sorghum stalks in general are characterized by relatively numerous stomates. Many sorghum cultivars have thick waxy coatings on stem surfaces, which is implicated in drought tolerance in the species. The formation of air-filled, cottony tissue has been noted in some sorghum stems as they mature (Freeman 1970). The accumulation of "diffuse" starch in the cells surrounding vascular bundles and in the parenchyma between the bundles occurs in sweet sorghum. Variations in leaf surface anatomy in sorghum may be helpful in classification (L. G. Clark pers. comm.). The leaf midrib color in sorghum has been associated with various characteristics such as stalk juiciness (Quinby and Schertz 1970) and digestibility (Kalton 1988). D. Chemical Composition Sweet sorghum stalks are juicier than "dry-stalked" grain-producing cultivars (Coleman 1970). In grain types, the concentration of sugar in the stalk remains less than that of the sweet type because greater quantities of sugars are consumed by the panicle in making starch in the seed. Since starch is a nonosmotic solid phase, grain types lose water as they mature, whereas sweet types retain water to balance sugar concentrations

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in the stalk. The sugar concentration at maturity of sweet sorghums ranges from 10% to greater than 25% of the plant sap. Stalk juiciness, as well as leaf midrib juiciness, are controlled by two independent loci; cultivars exhibita gradation between the two extremes (Quinby and Schertz 1970). Glucose and fructose are the predominant reducing sugars in the leaves and stalk. Sucrose is the predominant disaccharide. Starch occurs in the leaves and stem, although the concentration of stalk starch has been decreased with breeding efforts for suitable syrup cultivars (Wall and Blessin 1970). A similar result has been seen with the levels of aconitic acid in the stalk tissue; it is undesirable in syrup production (Coleman 1970). The starch content of the tissues decreases considerably as grain develops on sweet sorghum plants (Wall and Blessin 1970). In a study by Shaffer et al. (1992), cellulose, hemicellulose, and lignin made up 62.1 % of sweet sorghum stems and 54.1 % of the whole plant. The total structural component content was higher in stems than in leaf blades; stems had almost three times as much lignin as leaves. More cellulose was found in stems than in leaf blades; the reverse was true for hemicellulose. The rind fraction of the stem contained more structural components than the pith. These distribution relationships varied by cultivar (McBee and Miller 1990). Nonstructural carbohydrate levels were always higher in stems than in leaves. Nonstructural carbohydrate levels in leaf blades did not differ by cultivar. In stems, an inverse relationship between nonstructural carbohydrates and neutral detergent fiber concentration has been established (McBee and Miller 1990). A negative correlation was observed between the partitioning of nonstructural carbohydrate and structural carbohydrate; this relationship appears to be genetic and pleiotropic (Miller and McBee 1993). Cultivars of sweet sorghum were developed for production of refined sugar, but without commercial success. Cultivars developed for sugar production had greater percentages of soluable carbohydrates and lesser levels of fiber and nitrogen than syrup cultivars, but had 30% less total biomass production (Schaffert and Gourley 1982; Hawker 1985). Mature sweet sorghum grain may contain raffinose and stachyose in addition to starch, protein, and sucrose. Given the wide range in panicle and grain sizes, protein production in sweet sorghum varies widely (Wall and Blessin 1970). Glucose, fructose, and sucrose are the principal sugars in the developing sorghum caryopsis and the bract-pedicel unit. During seed formation, the concentration of reducing sugars is higher than that of sucrose in both organs. When starch begins to accumulate in the caryopsis, the level of sucrose in the caryopsis also rises and the amount of starch in the bract-pedicel decreases (Singh and

82


Asthir 1988). The percentage of total carbon partitioned to grain was similar if not greater in a study comparing a sweet sorghum hybrid with a grain sorghum hybrid (Vietor and Miller 1990). The concentration of nonstructural carbohydrates also was 1.4 and 2.7 times higher in the upper and lower internodes, respectively, of a sweet hybrid when compared to a grain hybrid. This indicates a higher potential for concentrating these carbohydrates in the sweet hybrid and/or a larger storage sink (Vietor and Miller 1990). Some sweet sorghum cultivars partition a significant amount of carbon to branches at the upper internodes. In general, mature stem tissue and branches proximal to the source leaf are sinks for nonstructural carbohydrate (Vietor and Miller 1990). Prior to anthesis, several leaves feed the panicle with equal strength as in grain sorghum. During grain filling, the panicle itself and the flag leaf contribute a large portion of photosynthate to the panicle (Eastin 1972). As long as the terminal meristem is developing, each internode will increase in biomass and the plant height will increase in late-maturing sweet sorghum cultivars (Coleman and Belcher 1952). Sugar continues to accumulate in fully developed internodes well into seed development. In another study, deheading a sweet sorghum cultivar increased the stalk sugar concentration but decreased the water content; therefore, the sugar yield was unaffected. However, lodging was decreased and branch production increased (Broadhead, 1973). The concentration of stalk sugar varies as the sweet sorghum plant develops (Hunter 1994). 'Waconia', an early cultivar adapted to Iowa, reached maximum sugar concentration during late August, about seven days after anthesis, and then sugar declined during seed filling. 'Waconia' produces a comparatively larger seed head that is fully mature by mid-September. 'Smith', a slightly later cultivar, had rapid rates of increase in stalk sugar concentration until about 10 days after anthesis and then began to decline. Later cultivars, such as 'Cowley', 'M81E', and 'Grassl' (the latest cultivar used), headed later and continued to increase sugar concentration in stalks up to time of harvest in mid-September when these cultivars were grown at higher latitudes than their zone of adaptation. The total sugar concentration between the dough stage and physiological maturity was shown to nearly double over that between the milk and dough stages (Wall and Blessin 1970). Lingle (1987) found a sevenfold increase in sucrose concentration between the boot and midgrain filling stages. The total sugar content of whole stalks was lowest at the boot stage and highest at soft dough. Sucrose predominated at all stages, although it was only 50% of the total soluble sugar in plants in the boot stage; glucose and fructose accounted for the remainder. Glucose was slightly higher than fructose at all stages; they both decline after anthe-

3. SWEET SORGHUM

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sis (Lingle 1987). McBee and Miller (1982) found that sucrose exhibited the most consistent diurnal and seasonal patterns at anthesis of all the sugars; glucose had the most variation due to its high demand in other metabolic pathways. A highly significant positive correlation (r 0.98) was found between sucrose and total sugars (Krishnaveni et al. 1990). The amount of sucrose synthesized in the tissue of mature plants exceeds that which could have been accounted for by the decrease in reducing sugars (Ventre et al. 1948). McBee and Miller (1982) suggested that sweet sorghum cultivars may inherently vary in production of mono- and disaccharides. They found this to be especially true for glucose concentration. Finally, soluble carbohydrate concentrations are not uniform within the stems of sweet sorghum cultivars (McBee and Miller 1982). It has been noted that the upper internodes have a greater total sugar concentration and greater sucrose concentration than the lower internodes at physiological maturity (Coleman 1970). In plants with 11 internodes, the highest concentration of sugar was found in internode 7 (Krishnaveni et al. 1990). The distribution of carbohydrate also changes over time. Prior to the panicle emergence, the final internodes are still elongating and laying down new tissue. These internodes became the most enzymatically active and strongest sinks (Lingle 1987). The onset of the reproductive phase is associated with the accumulation of sucrose and the termination of internodal growth. Before anthesis, sucrose accumulation is slow due to the competition by elongating internodes; after heading, sucrose accumulates because the panicle is a less competitive sink (Lingle 1987). Sucrose storage in sweet sorghum appears to be biochemically different than in sugarcane. In a study by Lingle (1987), there was no relationship between sucrose concentration and neutral invertase activity or between sucrose-phosphate synthase and sucrose accumulation. This is an indication that sucrose cleavage is not required for uptake in sweet sorghum parenchyma as it is in sugarcane (Lingle 1986). These results suggest diffusion as a transport mechanism for sucrose in sweet sorghum, or an active sucrose transporter at the plasmalemma or tonoplast. The differences in sugar accumulation in sweet sorghum and sugarcane stalks may be due to differences in the competitiveness of elongating and mature internodes (Lingle 1987). In a study comparing sweet and grain sorghum cultivars, elongating internodes of sweet sorghum had the highest activities of acid and neutral invertase and sucrose synthase, but with little accumulation of sucrose (Tarpley et al. 1994). A metabolic change occurred with the onset of reproduction and nonstructural carbohydrate storage. In the panicle, acid invertase, neutral invertase, and sucrose synthase activity

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E. L. HUNTER AND 1. C. ANDERSON

increased with the rapid growth of the inflorescence, then declined during grain filling. Soluble invertase, not sucrose synthase, was suggested as the first step in sucrose metabolism in the panicle (Tarpley et al. 1994). In the stalk, a decline in sucrose synthase levels as well as the low levels of the invertases appears to be an irreversible event and a prerequisite for the transition from internode growth to sucrose storage (Tarpley et al. 1994). These low enzymatic activity levels suggest that the sorghum stalk is a quiescent sink, as described by Sung et al. (19S9). However, the decline in sucrose-degrading activities did not account for differences among sorghum cultivars in sucrose storage ability; mechanisms beyond sink strength and enzymatic activity are necessary to explain the higher rates of sucrose accumulation in sweet sorghum than in grain sorghum (Tarpley et al. 1994). III. CROP PHYSIOLOGY In a study comparing growth of sweet and forage sorghum, Ferarris and Charles-Edwards (19S6a) found that each cultivar exhibited "spacesaving" plasticity. Plants grown at lower densities compensated by producing more and heavier stems at maturity. This resulted in a higher efficiency of solar radiation use during the maturation period. A forage sorghum might be expected to produce more leaf mass than a sweet sorghum cultivar due to selection for grazing (i.e., more tillers and branches). However, leaf area for the sweet sorghum cultivar was greater before anthesis. At anthesis, the forage sorghum produced more tillers and ultimately the two types of cultivars partitioned similar amounts of above-ground dry matter to leaf tissue (Ferarris and Charles-Edwards 19S6a). The stems and leaves of sweet sorghum are considered nonsenescent; they are photosynthetically active after the grain is mature (Nan and Ma 19S9). Grain sorghum cultivars are more similar to sweet sorghum in morphology and leaf architecture than to the forage types. However, Vietor and Miller (1990) found that leaf area in a sweet sorghum cultivar was twice that of a grain hybrid. Even when the sweet sorghum cultivar was defoliated to equalize the differences in leaf area, it accumulated twice as much nonstructural carbohydrate in upper parts of the stems (Vietor and Miller 1990). Starch levels increased similarly in both types of cultivars until anthesis (McBee and Miller 19S2), and total nonstructural carbohydrates were similar at the preboot stage (Vietor and Miller 1990). After anthesis and throughout the maturation period, however, concentrations of nonstructural carbohydrates were approximately two

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times greater in sweet sorghum than in grain sorghum representatives (Vietor and Miller 1990). McBee et al. (1983) suggested that after anthesis, assimilate production in sweet sorghum is in excess of the sink demand of the panicle and the levels of nonstructural carbohydrate accumulate in the upper stems. In the forage and sweet sorghum comparison, distribution of sugars was similar before anthesis; but, when mature, the sugar concentration in the sweet sorghum cultivar was 10 times higher than that of the forage sorghum (Ferarris and Charles-Edwards 1986b). In comparing a sweet sorghum hybrid with a grain sorghum hybrid, the carbon exchange rate (CER) of the upper and lower leaves declined two and three times more rapidly, respectively, in the grain sorghum (Vietor and Miller 1990). Higher CER ofthe sweet hybrid was associated with greater amounts of nonstructural carbohydrate after maturity; a greater, nonsenescing leaf area indicated a nonlimited source (Vietor and Miller 1990). When assimilation rates were regressed on conductance, the two were highly correlated. The slopes differed by species and by environment' thus indicating differences in intrinsic gas exchange efficiency (Kidambi et al. 1990). Wiedenfeld (1984) found that N uptake in sweet sorghum did not increase when levels of available N were increased from 112 to 224 kg ha- 1 and that uptake efficiency decreased by one half. In comparing N use by forage sorghum with sweet sorghum, differences were noted in partitioning patterns due to morphology (Ferarris and Charles-Edwards 1986b). Genotypic differences in remobilization of N from different plant tissues were also observed. However, there was little difference between cultivars in N concentration and its logarithmic decrease over time (Ferarris and Charles-Edwards 1986b). The differences arise in the amount of carbon gained per unit N taken up, especially in early growth stages. Extremely high rates of N application affected the distribution of N in the above-ground plant tissues and decreased the total dissolved solids in the juice of the sweet sorghum cultivars (Wiedenfeld 1984). Water-use efficiency in grain sorghum has been well characterized (Hattendorf et al. 1988; Bremner and Preston 1990; Kidambi et al. 1990). In a study comparing a grain sorghum and a sunflower hybrid (Helianthus annuus L.), both characterized by high water-use efficiencies, sorghum exhibited a greater grain-yield increase than sunflower after a long period of drought-induced arrested development that was broken by watering, showing the greater ability of sorghum to undergo arrested growth dormancy (Bremner and Preston 1990). In the southeastern United States, interest in sweet sorghum as an interim crop in sugarcane (Saccharum officinarum L.) and vegetable production systems has increased. Water management also is an issue in this region. Shih (1986) showed that the

86


water-use efficiency of sweet sorghum was inversely related to water table depth. A whole-plant simulation model was designed to investigate interactive water stress responses (McCree et al. 1990). In sorghum, low stomatal conductance was the primary factor determining its low water use per carbon gain in unstressed as well as stressed conditions (McCree et al. 1990). Patterns of dry-matter accumulation are directly proportional to the amount of solar radiation intercepted by the crop (McGowan et al. 1991). More specifically, total dry matter is the product of intercepted photosynthetically active radiation (PAR) and radiation use efficiency (RUE). The RUE was shown to differ by genotype in grain sorghum (Hammer and Vanderlip 1989). There also were interactions with temperature, but the physiological explanations remain elusive. Temperature has an effect on the rate of development in grain sorghum (Hammer et al. 1989). This is particularly the case in the period of time between emergence and anthesis, a critical period when crop growth rates are highest in sorghum and the number of leaf nodes is determined. Temperature effects also generally predominate over photoperiod effects in sweet sorghum development during this time, as would be expected in the growth of an unmodified tropical species grown in the Midwest. Photoperiod has been implicated as the dominant environmental influence during the reproductive period (Coleman and Belcher 1952). Ultimately, soluble carbohydrate yields are greatest in sweet sorghum (and other sorghum) cultivars where phenological development is synchronized with an environment such that high-incident radiation coincides with a long preanthesis growth period (Ferarris and Charles-Edwards 1986b). Radiation received during fruiting has the greatest influence on dry matter yield. This was shown to be a linear relationship, with approximately 1.4 kg ha-1 of sweet sorghum produced per 4.2 Jm-2 of solar radiation (Hipp et al. 1970). In forage and sweet sorghum cultivars, the rate of accumulation of sugars is constant; therefore, dry-matter differences are expressed in intercepted PAR-use efficiency terms (Ferarris and CharlesEdwards 1986b). For sweet sorghum lines, 95% of the PAR intercepted was utilized in increasing the pools of soluble sugars (versus 5% for the forage type). On the other hand, PAR-use efficiency for N is not significantly different by sorghum type. The PAR-use efficiency also changed over time. It was greatest during maturation when radiation and leaf area values are high and growth rates have decreased (Ferarris and CharlesEdwards 1986a). Several crop growth models have been proposed for sorghum. Shih et al. (1981) modeled the production of biomass in sweet sorghum cultivars. Early growth was dominated by leaf expansion; the later growth

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phase was characterized by high rates of stalk growth and dry matter accumulation. The pivotal components in establishing yields were dry leaf biomass accumulation, leaf dry biomass, leaf area index, and their specific relationships to total dry biomass. In addition to its use in simulating water-use efficiency, the model by McCree et al. (1990) also considered the interacting effects of respiration on the carbon-use efficiency in specific tissues. A linear function has been developed to describe the effect of daily average temperatures on the rate of development in grain sorghum (Hammer et al. 1989). Bender et al. (1983) assumed that the phenology of sweet sorghum and grain sorghum is mostly determined by temperature. They proposed a growth model that used the modifications of leaf area to stalk length ratios as suggested by Shih et al. (1981). They also modified the leaf extinction calculation and changed the proportion of dry matter partitioned between plant parts as compared to that used by Vanderlip (1972) for grain sorghum. Considering the fact that the flowering of a sorghum population is not completely synchronous, the model predicted the half-bloom stage and physiological maturity with accuracy. Dry matter partitioning also was predicted with confidence. The proportion of dry matter diverted to the stalk was substantially greater than in previous models. Wiedenfeld (1984) found that the dry matter production allocated to stalks in sweet sorghum ranged from 55 to 60%, from 29 to 32% for leaves, and from 5 to 12% for panicles. Although more work needs to be done on the partitioning of dry matter into fermentable versus nonfermentable portions, the authors stated that the model was adequate for use in scheduling sweet sorghum harvests (Bender et al. 1983). IV. GENETIC IMPROVEMENT In the 1950s and 1960s, the U.S. Sugar Crops Field Station at Meridian, Mississippi, released several cultivars that produced good-quality syrup. These cultivars were created utilizing exotic germplasm from the approximately 1,200 cultivars collected in Africa by Carl O. Grassl in the 1940s. This material was helpful in increasing resistance to leaf anthracnose and stalk red rot, both caused by Colletotrichum graminicolum (Ces) G. W. Wils. This disease was one of the primary causes of yield reduction. The new material also was used to increase plant height and decrease days to maturity, as well as to increase resistance to rust, zonate leaf spot, downy mildew, Maize Dwarf Mosaic Virus, and cotton insecticides (Coleman 1970). Breeding programs in Texas and Louisiana contributed new sugar and syrup cultivars in the 1960s. 1. E. Stokes, O. H. Coleman, and

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D. M. Broadhead kept the interest in sweet sorghum alive by releasing several high-sugar cultivars in the 1950 and 1960s, including 'Sart', 'Tracy', 'Wiley', and 'Brandes' (Coleman 1970). Many of these are utilized in current breeding programs. Other qualities that were considered in the evaluation of new cultivars are harvestability and extractability of the juice (Coleman 1970) and bacterial leaf diseases (Kuepper 1992). In the United States, the first efforts in sweet sorghum cultivar improvement began in the 1880s for table sugar production rather than for sorghum syrup. Most of the foundation seed came from Leonard Wray's South African collection or from a few Asian cultivars (Coleman 1970). These efforts ended in the 1890s as it was seen as an unprofitable endeavor. However, use of sweet sorghum for syrup and forage increased. In the 1940s, during World War II, sweet sorghum was once again considered a sugar source. The selections were made by the USDA and the Kansas State University Agricultural Station. Since that time, the USDA station at Meridian, Mississippi, has worked on developing sugar cultivars that are high yielding and disease resistant (Coleman 1970). Cultivars developed for sugar production must have a high purity (the ratio of sucrose to total sugar), a low rate of sucrose inversion, and low levels of starch. The presence of starch in the juice disrupts the formation of crystalline sucrose. The high levels of aconitic acid present in some cultivars also interfere with sugar refinement. Since no inexpensive way to remove starch and aconitic acid has been developed, interest in sweet sorghum as a sugar crop has greatly diminished (Coleman 1970). 'Rio' was released in 1965 as a sugar crop and remains an important cultivar (Coleman 1970). Periodically, cultivars that are characterized by a high sucrose content are still released. Most cultivars are open-pollinated. Producers of sorghum syrup grow a mixture of traditional and improved cultivars. Traditional cultivars are those that have been heavily relied on and consistently produce highquality syrup. Traditionally, experienced producers have been good seed savers and do some of their own selections in the field. Of the traditional cultivars commonly grown for syrup and silage, many are in the 'Orange' and 'Amber' groups. However, some of the common names of cultivars overlap and are used more informally (Kuepper 1992). 'Sugar Drip' is another commonly grown traditional cultivar. It originated in Zaire and is one of the few available commercially (Kuepper 1992). 'Dale' is probably the most widely grown cultivar. It was released in 1970 as a midseason cultivar with high disease resistance (Broadhead et al. 1970). Major advances in sorghum breeding were made in a project by Stephens et al. (1967). Using a vast array of germplasm, many short, early sorghums were produced that have been especially productive in the

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temperate zone. The vulnerability of sorghum cultivars to diseases and pathogens was reduced as a result of this use of a wide germplasm base. In the sweet sorghums, there is a positive correlation between plant height and yield, and plant height and maturity are positively correlated traits (Miller and McBee 1993). Planting late-maturing sweet sorghum cultivars in areas with long day lengths increases yields. In contrast to grain sorghum where response to photoperiod is sometimes selected against, the response to photoperiod is intentionally retained and manipulated in some sweet sorghum. Thus, in addition to plant breeding, management practices are used to maximize yields (Miller and McBee 1993).

Sweet sorghum programs have combined desirable traits in the traditional cultivars and those in wild relatives to improve cultivars for sugar production (Kuepper 1992). Manipulation of the wealth of variation in S. bicolor has resulted in highly divergent resources in plant morphology and composition. Major recent breeding efforts have focused on disease resistance, lodging resistance, and increasing seedling vigor (Kuepper 1992). The United States has been upgrading the management of its sorghum germplasm collection; the 38,000 accessions have been inventoried and separated into groups (Dahlberg et al 1993). The collection has been consolidated at the Southern Regional Plant Introduction Station in Griffin, Georgia. At least 100 to 200 of these accessions are juicy stalked. In the India sorghum germplasm collection, which consists of approximately 7,000 accessions, over 3.5% of the cultivars tested have been shown to be sweet stalked. Most sorghums grown in India serve as dual sources of grain and fodder. Sweet-stalked cultivars are planted sparsely among the cultivated grain types. Most of the sweetstalked accessions tested were of the Caudatum and Dura races and originated in the Sudan, Cameroon, Ethiopia, India, and the United States (Rao and Murty, 1981). Evidence is mounting that the wild sorghum races may be ample sources of genes for pest resistance, environmental adaptation, and high productivity (Bramel-Cox and Cox 1988). There are wild-type accessions in world collections and in use in farmers' fields. There has already been some purposeful introgression of wild germplasm in addition to the more traditional use of exotic accessions (Bramel-Cox and Cox 1988). The interest in "high-energy" sorghum hybrids has increased. These hybrids utilize a grain-type seed parent and a sweet-type pollen parent. The product is taller than the seed parent and has increased stalk sugar concentrations (Miller and McBee 1993). The grain yields approach those of the seed parent. When pollen parents have inherently high nonstructural carbohydrate levels, the hybrid will most likely also have

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high nonstructural carbohydrate concentrations. Female parents may also enhance sugar production (Miller and McBee 1993). The use of cytoplasmic male sterility is critical in the production of sorghum hybrids. Typically, in grain sorghum hybrids, a milo (race Dura) cytoplasmic male-sterile system is used to induce sterility in most female parents of hybrids. Kafir derivatives with nuclear restorer genes are used as maintainers (Schertz and Pring 1982). Alternative systems consisting of both nuclear and cytoplasmic are being sought to improve germplasm diversity (Schertz and Pring 1982). Unlike maize inbreds, inbred parental lines of sorghum hybrids are reasonably vigorous (Miller and McBee 1993). Wild germplasm may serve as a new source of male-sterile cytoplasms. The use of wild germplasm may preserve alleles for which there is no current need, but which may have a future purpose, and those not already maintained as the cultivated crop has evolved (Bramel-Cox and Cox 1988). Work was done on male-sterile and hybrid sweet sorghum at the Meridian, Mississippi, Agricultural Station. This program was moved to the University of Georgia Experiment Station and is ongoing. Most recently, breeding programs have focused on the production of multipurpose cultivars for use as energy and sugar crops. These highyielding cultivars are oftnn tall and have increased soluble carbohydrate concentrations and decreased structural carbohydrate levels due to the inclusion of tropical genetic material. Therefore, they are often prone to lodging. Breeding efforts have focused on lodging resistance. A cultivar may exhibit resistance to lodging due to a strong root system, strong stalks, flexible stalks, or smaller and more compact panicles (Coleman 1970). However, stalks that are too hard may impede the expression of juice (Coleman, 1970). In 1981, the U.S. Sugar Crops Field Station at Meridian, Mississippi, in cooperation with the breeding program of the Crops Research Division of the USDA-ARS and the Mississippi Agricultural and Forestry Experiment Station (MAFES), released 'M81E', a cultivar for syrup and fermentable carbohydrate production (Broadhead et al. 1981). MAFES is one of the leading producers offoundation seed stocks. In 1987, cultivar 'Smith' was released through the cooperative research programs of the Texas Agricultural Experiment Station and USDA-ARS for sucrose and biomass energy production (Kresovich and Broadhead 1988). 'Della', another popular syrup cultivar, was improved and released in 1990 by Robert Harrison in Virginia (Kuepper 1992). Another cultivar, 'Top 76-6', was released jointly by the University of Georgia, USDA, and Mississippi State University in 1994 (Day et al. 1995).

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V. SYRUP PRODUCTION

A. Sweet Sorghum Culture Sweet sorghum cultivars that can be used successfully in syrup production are those that need little skimming of coagulated material when cooking down and that produce syrups light in color. Excess nitrogen can affect syrup quality. It is not advisable to plant sweet sorghum after a legume green-manure crop. Droughty conditions also affect syrup quality. Late-season moisture stress causes dormancy in the panicle; late rains may restore growth and development and initiate the growth of secondary heads and new tillers (Kuepper 199Z). Producers use various planting methods: drilling in rows, planting in furrows (listing), and skip-row planting. In skip-row planting, four to eight rows are planted and two are skipped. In skip-row planting, yields are generally not decreased due to the production of heavier stalks in the outside rows. Producers often include sweet sorghum production in an appropriate rotation for improved pest and disease (fungal, bacterial, and viral) control (Kuepper 199Z). Yields are limited by the potential diameter of the stalk and the tillering ability or the gap-filling capacity of a cultivar. Syrup and sugar producers generally harvest when the plants are in the soft dough stage. Several cultivars, varying in maturity, can be planted to lengthen the production season (Kuepper 199Z). Sweet sorghum production has been a long tradition in the southeast, mid-South and the lower Midwest of the United States (Kuepper 199Z). Production in the United States declined severely in the 1970s and has been on the increase since then. The number of hectares in sweet sorghum production in the United States peaked at 141,643 in the 1930s (Coleman 1970) and decreased to less than 400 ha in 1987 (Bureau ofthe Census 1987). For example, in Kentucky, almost 9,000 ha of sweet sorghum were planted in 1899. This decreased to ZOO in 197Z and then increased to over 600 in 199Z (Kuepper 199Z). Currently, a typical syrup producer in the National Sweet Sorghum Producers and Processors Association grows less than Zha of sweet sorghum and produces less than 900 liters ha-1 (NSSPPA 1994). In 1986, eight states accounted for 90% ofthe total syrup production in the United States: Alabama, Arkansas, Georgia, Iowa, Kentucky, Mississippi, North Carolina, and Tennessee (Freeman et al. 1986). Tennessee and Kentucky were the leading producers throughout the 1980s (Bureau of the Census 1987). Sorghum syrup production is no longer included in USDA crop reporting statistics. However, in 1995, the National Sweet Sorghum Producers and Processors listed 17

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states as sorghum syrup producers and marketers. Interest in sweet sorghum production has been renewed due to its drought tolerance and high N and radiation use efficiencies. Currently, it is predominantly used for feed in the South, either as silage or for syrup to sweeten grain feeds. Interest in local production for human use as a sweetener with nutritional value has also increased (Kuepper 1992). Historically, sweet sorghum production for syrup has involved specific cultural practices. Producers observe that excess nitrates and cultivar selection both affect syrup quality. Syrup producers generally apply 34 to 56 kg ha- 1 of fertilizer N (Kuepper 1992). Some use planting patterns to facilitate the removal of panicles and leaves at harvest such as skip-row planting. Management is generally determined by an emphasis on maximum total yield, not by a particular plant organ or an aesthetic attribute. Studies have shown that early planting increases sugar yields at harvest (Broadhead 1969; Lueschen et al. 1991). Fermentable carbohydrate concentrations were increased by 13% in early plantings over late plantings (Lueschen et al. 1991). However, soil temperatures should be at least 18°C at planting time to ensure adequate stands. Sorghum seedlings are not vigorous in cool, wet conditions (Kuepper 1992). In general, planting dates should be planned so that close to the maximum solar radiation is received by the crop in the period between boot and early seed formation (Hipp et al. 1970). Numerous studies have been done on the effects of plant spacing on sugar yields in sweet sorghum. Lueschen et al. (1991) and Broadhead et al. (1963) found that planting densities only slightly affect sweet sorghum sugar yields. Seed cost became the more important factor. In a grain sorghum study, McGowan et al. (1991) reported a decrease in dry matter yield when sorghum was planted in wide rows (1.5 m). McBee and Miller (1982) found that plants in narrower rows (25 cm) had higher total nonstructural carbohydrate levels, both preboot and at anthesis, than those in wider (100 cm) rows. In another study, Miller and McBee (1993) found that wider spacing increased the structural carbohydrate levels. Therefore, they concluded that planting geometries could be used to alter the partitioning of photosynthate between structural or nonstructural carbohydrates. There may be additional benefits in adjusting plant spacing, such as improving water-use efficiency and decreasing lodging (McGowan et al. 1991). In general, dry matter accumulation is related more directly to the amount of solar radiation intercepted than to row spacing. Sorghum plants adapt by an unknown mechanism to the row width and population density by altering leaf and tiller production (McGowan et al. 1991). Ultimately, sugar yields are determined by stalk diameter/storage capacity and the ability to produce tillers (Coleman 1970).

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Sweet sorghum can be sown and cultivated with conventional equipment. Sweet sorghum planting can be scheduled after other crops have been planted. Since it is largely a self-pollinated plant, seed can be saved each year for the following cropping season. Recommended row width is 75 to 100 cm and recommended densities are similar to grain sorghum, 6 to 10 plants row-m- 1 (Kuepper 1992). Planting depth is 2.5 to 4 cm depending on the soil type (Freeman et al. 1986). Sweet sorghum should be cultivated as frequently as possible for weed control, especially in herbicide-free production. Due to its low rate of growth early in the season, canopy closure is delayed compared to other crops. Sweet sorghum can be grown following winter rye, or intercropped with perennial crops; this is a way of increasing productivity when biomass systems are considered. These cultural characteristics, along with modest water requirements, indicate that sweet sorghum production is potentially energy and cost efficient. General experience has shown that sweet sorghum requires only moderate amounts of N fertilizer. Several cultivars have been shown to respond to 112 kg N ha-1 by altering the distribution of biomass between plant tissue types (Wiedenfeld 1984). Smith and Buxton (1993) found that N amendments had no significant effect on sugar yields. Lueschen et al. (1991) also noted that N fertilization was not a determinant ofthe ethanol potential (or soluble carbohydrate production) of sweet sorghum. The residual soil N levels of 90 kg ha- 1 appeared to be sufficient. California studies have shown that sweet sorghum requires 37% of the fertilizer N used by maize (Hills et al. 1990). Sweet sorghum also requires 33% of the N used in sugarcane production (Coleman 1970). Based on comparable theoretical ethanol yields, 190 kg, 140 kg, and approximately 90 kg N ha- 1 are necessary for maize, grain sorghum, and sweet sorghum, respectively (Wiedenfeld 1984). A study by the authors on biomass crops indicated that sweet sorghum grown in a monoculture does not respond to N rates greater than 80 kg ha-1 , or 55 kg ha- 1 following soybeans in a rotation. Thus, Putnam et al. (1991) described sweet sorghum as having a high ratio of crop cultural energy per unit of N fertilizer. Weed control options for sweet sorghum are limited. Propazine was commonly used for weed control but its continued registration is doubtful. Efforts have been made to reregister it as well as to allow the use of metolachlor and alachlor for weed control in sweet sorghum. Atrazine has also been used but is not registered for sweet sorghum syrup. There also is a need for a seed safener that is certified for sweet sorghum. The use of oxobetrinil as a safener has shown promise. Various plant growth regulators have been tested on sweet sorghum to increase sugar production. In a study in Florida, glyphosate, glyphosine,

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ethephon, and mefluidide were applied to sweet sorghum and the effects on juice content, Brix, and dry matter production were determined (Prine et al. 1988). None of the parameters were negatively affected; mefluidide appeared to increase the juice content and dry matter yield. Glyphosine has shown promise as a sugar ripener in sweet sorghum when used in a manner similar to the sugarcane industry. Ethephon has been used effectively to decrease lodging in tall, southern, and tropical sweet sorghum cultivars. Dry matter and sugar yields of plants treated with 0.14 and 0.28 kg ha- 1 of ethephon were not different than controls. Lodging was effectively controlled at the 0.14 and 0.28 rates, depending on the cultivar (Hunter et al. 1993). There was some indication that ethephon may increase sugar concentrations. B. Harvesting and Processing Historically, syrup production has been a community activity with intensive labor needed for several months in the fall. Stalks were brought to a mill owned by several farmers where they were milled and cooked. Often, 40 to 60% of the syrup was retained by the mill owners as payment (Kuepper 1992). Although the best stage for harvesting sweet sorghum is the soft-tohard dough stage, cultivars vary in sugar concentrations when compared at specific stages of maturity. For example, 'Sugar Drip' may produce a quality syrup when harvested in the late milk stage. However, 'Dale' produces the highest quality syrup when harvested later than average, or close to the hard-dough stage (Bitzer and Fox 1987). Some cultivars can be harvested for sugar any time between anthesis and the dough stage (Coleman 1970). In more northern climates, the grain may be at physiological maturity before the cultivar is at peak sugar yield (Coleman 1970). For syrup production, sweet sorghum juice should have enough starch to give the syrup an adequate viscosity, but not enough to cause gelling. Too much aconitic acid in the juice will cause a bitter taste in the syrup (Coleman 1970). Harvesting at the optimal maturity/peak sugar concentrations, removing the panicle and peduncle, and stripping the leaves of the stalks are all practices that aid in reducing the starch content of the plant sap and avoiding undesirable tastes in the syrup (Coleman 1970; Kuepper 1992). Sickle bars have been designed to remove panicles mechanically, but a method of leaf stripping has not been developed to make it economical on a large scale (Kuepper 1992). Thus, several additional practices help prevent the formation of high levels of starch: allowing the leaves to wilt thoroughly on the cut stalks (2-10 days), letting the

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extracted juice settle for at least 2 h, and adding a commercial amylase during the preheating of the juice to break down the starch (Kuepper 1992). Letting the stalks sit in piles for 3 to 5 days also allows for the conversion of sucrose to fructose and glucose by the action of invertase; this practice decreases the risk of crystalization of sucrose in the syrup (Kuepper 1992). However, very large producers (growing more than 12 hal are best served in using a harvesting system where the stalks are mechanically chopped as 15- to 20-cm-long billets (Bitzer and Fox 1987). Billets must be processed in a timely manner since spoilage occurs in damaged tissue. Harvesting the stalk in sections allows the separation of stalk pieces from the leaves and seed. Shakers and blowers are also required to remove leaves and other debris before milling (Wright et al. 1976). The standard method of juice extraction is the three-roller mill. Typically, vertical mills have been used in small mule or horse-powered operations. These mills are 30 to 40% efficient in expression of stalk sap and are seen mostly at demonstrations and festivals or on display (Kuepper 1992). Most producers use horizontal, stationary mills powered by steam engines, motors, or hydraulics and driven with belts, pulleys, and gear reduction systems (Kuepper 1992). These mills usually have a 50% or greater juice expression efficiency. In a three-roller mill, there is one top roller (sometimes stationary), a feed roller (separated from the top roller by a l-cm gap), and an extraction roller below (separated from the top roller by a 0.16-cm gap) (Bitzer and Fox 1987). Small producers have at least one mill, sometimes portable, with a feed roller that is 30 to 45 cm in length and 15 to 30 cm in diameter. A large producer might have one or more power mills with feed rollers up to 60 cm in length and 30 cm in diameter. Since no new mills are commercially available, producers often depend on the rejuvenation of old mills or building new mills by hand (Bitzer and Fox, 1987). The efficiency of the mill is determined by the speed of the rollers, the spacing of the rollers, and the feeding rate. Feeding should be continuous. An adequate goal for efficient pressing is to separate 50 to 55 kg of juice from 100 kg of stalks (Bitzer and Fox 1987). The ultimate solution to efficiency is field milling where only the juice is removed from the field, saving time and money (Kuepper 1992). Small, portable evaporators may also be used (Coleman 1970). However, the intended use ofthe bagasse, or residue left after pressing the juice out of the stalk, must be considered. It may be used in the production of steam to run the mill, reincorporated into the field, or combined with the seed heads to be ensiled for feed or alcohol production. The best results are achieved when gravity is used as much as possible to move the juice during cooking. Juice may be stored cold to allow

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the settling of solids. At least 2 h should be allotted to settling. The juice often has been filtered two times prior to this phase. Amylase may be added at this point with agitation (Kuepper 1992). The optimal amount of juice storage space is that which would allow 2 to 3 h of milling. Storage for more than 3 h without cooling or preheating may cause some spoilage. In larger operations, the juice is preheated in a separate tank in order to increase activity of added amylase and to skim off coagulated solids (Kuepper 1992). Traditional harvesting methods are being revised in order to increase mechanization. Milling and press design are also receiving increased attention. New methods of handling the increased tonnage produced by new cultivars are needed. Like maple syrup, sweet sorghum syrup is produced through an evaporative process. The type of evaporator pan and heat source used are dependent on the size of operation and preference. Evaporators used include batch and continuous-flow types. The most common design is the 3.5 m continuous-flow evaporator. The ideal construction material is stainless steel (Bitzer and Fox 1987). Small producers often use a batch system in a flat-bottomed pan mounted on a wood firebox (Wigginton 1975). Continuous-flow pans vary considerably in design based on the number and arrangement of dividers or baffles for controlling the movement of the juice, semisyrup, and syrup stages through the pan. The "Stubbs" evaporator is divided in half lengthwise such that juice enters on one end and travels the length of the pan, is clarified, and returns on the other side to the end as finished syrup (Coleman 1970). More elaborate evaporators utilize a system with a series of baffles running the width of the pan, with the openings alternating on either side. Cooking in these pans can be done on an inclined or flat plane. The juice is advanced through with scoops, push rags, and dams as it reaches different stages of development. The pan may have self-skimming trays on the sides and a water bath under the final compartment to moderate the temperature of the finished syrup and to prevent scorching (Kuepper 1992). Flat pans are operated using "batch sections." Intermediate- to large-scale syrup producers often use multiple-pan cooking systems. After preheating, skimming, and filtration, there are one to many separate semisyrup batch pans and a finishing batch pan (Kuepper 1992). Finishing and cooling may be done with a vacuum pan; a vacuum allows the use of lower temperatures (Coleman 1970). Fuel options for small- to moderate-sized producers or those using one pan on a firebox are natural gas, petroleum fuel, and firewood, including sawmill discards. The reliance on these sources will depend on future supplies, economics, and environmental quality (Kuepper 1992). Fireboxes are often designed with a hill that climbs gradually at the juice

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end and then falls away just before the finished syrup end of the pan. This is to allow better control of heating the various sections of the pan (Kuepper 1992). The most efficient heat source for the evaporators is steam; this permits the best control of heat and the use of multiple-batch pans. Large-scale operations based on steam heat for evaporation (and often for powering the mill) increase in efficiency as the amount of bagasse-derived fuel used in the furnace increases (Kuepper 1992). Syrup quality is determined, to a large extent, by the experience of the processor. Otherwise, proper skimming (at peak coagulation), keeping the pan surface covered, and the use of optimal temperatures in each section of the pan help maintain the quality of the syrup (Kuepper 1992). The key to syrup character is fast cooking or little exposure to heat. Ideally, in a continuous pan the juice should enter in a small, steady stream and syrup should leave in a steady trickle (Kuepper 1992). A high boil should be maintained with a constant juice depth (Bitzer and Fox 1987). Overheating increases the production of undesirable color and flavor compounds (Kuepper 1992). Proper finishing temperatures allow the characteristic sorghum flavor to develop. The boiling point of sugar solutions is directly related to and increases with their density or concentration. Therefore, the use of continuous temperature readings is a way of regulating the stage of syrup development (Coleman 1970).Temperature probes and thermocouples allow these readings to be taken in very specific parts of the pan. A syrup refractometer can also be used to monitor the sugar concentration. The final boiling temperature should range from 108 to 110°C or final Brix readings of 78 to 80 C (Kuepper 1992). Traditionalists knew that the syrup was finished when the bubbles rising from the bottom were about 5 cm in diameter and burst in the middle (Wigginton 1975). The finished syrup is strained and cooled to 70 to 80°e. This cooling maintains the desired color (Bitzer and Fox 1987). Subsequent bottling at 65°C prevents microbial growth in the finished product. Invertase may be added at this point to prevent the crystalization of sucrose (Kuepper 1992). It takes 6 to 12 liters of juice to produce 1 liter of syrup (Bitzer and Fox 1987). This ratio depends on the Brix reading of the harvested juice and the amount of starch in the juice. Juice with a Brix reading of 16, the standard concentration used to determine the date of harvest, will yield 1 liter of syrup per 6.5 liters of juice (Kuepper 1992; NSSPPA 1974). The quality of sorghum syrup is judged first by color and second by taste. Good quality syrup should have a mild and sweet taste with the distinct sorghum flavor and be light amber in color. It should have very little aftertaste, as little crystallization as possible, and be fairly dense (Coleman 1970). D

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Traditionally, sorghum processing was, and still is to some extent, a community event. Processors were sometimes mobile, moving their mill (and sometimes evaporator) throughout an area and pressing and cooking an individual's sweet sorghum crops. The millowner often took one-fourth of the syrup in payment (Wigginton 1975). Alternately, farmer cooperatives were established with larger, stationary mills. Single mill owners also contracted local growers to produce sweet sorghum. If producers of syrup were good managers and chose appropriate cultivars and handling methods, a standard high-quality product resulted (Coleman 1970). Although some producer and processor cooperatives and corporations still exist, most sweet sorghum for syrup is grown by small- to intermediate-sized producers who supply a local demand (Bitzer 1987). Syrup production is increasingly community, family, and festival oriented. There is still interest in sweet sorghum as a source of processed sugar. With improved sugar extraction and crystallization methods, sweet sorghum could serve as a supplementary source of sugar in the sugarcane and sugarbeet industries. The same processing equipment could be used, thus extending the season and decreasing costs (Coleman 1970). C. Marketing and Distribution Sweet sorghum products are marketed through local festivals and local distributors and by direct marketing. Currently, the market greatly exceeds the production in some areas. The product is valued at about $4.50 per liter. With a potential of 1100 liters/ha-1 , the crop would have a gross value of $4,950 ha-1 (Kuepper 1992). Whereas there are few hectares that are contracted for sweet sorghum production, a single processor's syrup may be contracted to be distributed under multiple labels. Small-scale, local producers are well known and easily market their product. Larger cooperative groups distribute much of their product in a larger region. Blends of sorghum and other sweeteners have been created. Pure sorghum syrup has been sold under brand names (Coleman 1970). Efforts are being made by the National Sweet Sorghum Producers and Processors Association (NSSPPA 1994) to ensure the correct labeling of pure sorghum. Sometimes blends with corn syrup are erroneously labeled as pure sorghum. Syrup produced from sweet sorghum is a primary product, whereas molasses is a byproduct from cane sugar refining (Kuepper 1992). Thus, sorghum syrup potentially fills a health food niche as a natural sweetener with several nutrients. Traditionally, its use in the southern United States has been similar to that of maple syrup in the northern states. Sorghum

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has more calcium, iron, and potassium than sugarcane molasses, honey, or corn syrup (Vander Hart 1992). Also, there still is potential for sweet sorghum as a source of processed crystal sugar (Kuepper 1992). The greatest potential for sweet sorghum syrup is as a whole, unrefined sweetener, to fit into the expanding urban health food market. It may be possible to tailor syrup to gourmet tastes using traditional, heirloom cultivars as well as using the traditional four-pound-sorghum can and labeling styles associated with the gourmet market (Kuepper 1992). Those who use sorghum syrup in regions where it has been grown traditionally have developed specific tastes. Corn syrup has been blended with sorghum syrup to produce an improved product. A 40% blend of corn syrup with sorghum syrup has been shown to be the most satisfactory mixture. The product is less acidic, has a more appealing color and lower viscosity, and stores better than pure sorghum (Collins et al. 1980). Such blends can be used to extend the supply of sorghum and to make pure sorghum more acceptable to potential consumers. However, blending should not be a means of masking characteristics of low-quality sorghum syrup, as is often done. High-quality sorghum syrup should be used in blends in order to maintain high standards (Collins et al. 1980). There also is potential for sweet sorghum use in the food ingredient market (Kuepper 1992). In addition to undeveloped areas, there is evidence that in some regions demand is exceeding supply (Kuepper 1992). As a cash crop, sweet sorghum becomes significant because a farmer can market it directly and net more income from a value-added product. The largest barrier to expansion of markets is the standardization of quality. Each producer has a slightly different product. This difference becomes important when sales and consumption move out of a local region. Maintenance of syrup quality and purity of product will only be guaranteed if the wisdom and lore of sorghum syrup production and processing is passed on, intact, to younger producers. Organizations such as the NSSPPA help enable this process. VI. FUTURE PROSPECTS Sweet sorghum will continue in the United States as a specialty crop for sorghum syrup. The health food aspect of sorghum syrup, with its complex of organic and mineral nutrients, may increase use of the syrup. The sweetener and taste aspects may lead to new products with a distinctive taste. In some areas of the world, sweet sorghum is used intensively as a sugar crop. Sweet-stemmed sorghums are a major source of sugar to

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millions of Chinese. China has a cornucopia of sorghum types including sweet-"temmed sorghums (National Academy of Sciences 1996). Chinese sorghum represents the long separated Asian side of sorghum, and reuniting the genes of these with the African types could be useful in the future. For the United States and much of the world, sweet sorghum has the greatest potential of any crop to become a source of liquid fuels that are renewable. Sweet sorghum has large biomass yields with its rate of photosynthesis exceeding that of maize during the warmest parts of the summer. It has a high concentration of readily fermentable sugars similar to sugarcane. The residue remaining after distillation of ethanol is adequate to fuel the processing to ethanol. Sweet sorghum has a relatively short growing season of about two weeks later in the spring and in the fall two or more weeks earlier than maize and soybeans in the Midwest. It is considerably more tolerant to moisture stress than maize. It requires less than 50% of the nitrogen fertilizer needed for maize. It is amazingly adapted to a wide range of latitudes, whereas sugarcane is limited to tropical climates. Its culture is simpler and less expensive than that of sugarcane since it is grown from seed rather than as stalk pieces. In addition, a crop of sweet sorghum for fuel would have some grain for food or feed (Hills et al. 1990). For latitudes greater than 45°C, the growth rate of sorghum will be limited by temperature and, therefore, beets or cellulosic crops would be better sources of liquid fuels. LITERATURE CITED Bender, D. A., R. 1. Vanderlip, G. A. Smith, M. O. Bagby, and R. M. Peart. 1983. Simulating the growth and development of sweet sorghum. ASAE Paper 83-3022. ASAE, St. Joseph, MI. Bitzer, M. J. 1987. Production of sweet sorghum for syrup in Kentucky. Ext. Servo Publ. AGR-122, Univ. Kentucky Ext. Serv., Lexington. Bitzer, M. J., and J. D. Fox. 1987. Processing sweet sorghum for syrup. Ext. Servo Publ AGR123. Univ. Kentucky Ext. Serv., Lexington. Bramel-Cox, P. J., and T. S. Cox. 1988. Use of wild germplasm in sorghum improvement. p. 13-26. In: D. Wilkinson, (ed.), Proc. Forty-third Annual Corn and Sorghum Research Conference, 8-9 December 1988, Chicago, 11. American Seed Trade Association, Washington, DC. Bremner, J. M., and G. K. Preston. 1990. A field comparison of sunflower (Helianthus annuus) and sorghum (Sorghum bicolor) in a long drying cycle. II. Plant water relations, growth and yield. Austral. J. Agr. Res. 41:463-478. Broadhead, D. M. 1969. Sugar production from sweet sorghum as affected by planting date, after-ripe harvesting, and storage. Agron. J. 61:811-812. Broadhead, D. M. 1973. Effects of deheading on stalk yield and juice quality of Rio sweet sorghum. Crop Sci. 13:395-396.

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Broadhead, D. M., O. H. Coleman, and K. C. Freeman. 1970. 'Dale'-A new variety of sweet sorghum for syrup production. Miss. State. Expt. Sta. Inform. Sheet 1099. Broadhead, D. M., K. C. Freeman, and N. Zummo. 1981. 'M81E'-A new variety of sweet sorghum. Miss. Agr. and For. Expt. Sta. Inform. Sheet 1309. Broadhead, D. M., I. E. Stokes, and K. C. Freeman. 1963. Sorgo spacing experiments in Mississippi. Agron. J. 55:164-166. Bunting, A. H. 1990. The pleasures of diversity. BioI. J. Linnean Soc. 39:79-87. Bureau ofthe Census. 1987. Census of Agriculture Volume I. Geographic area series, part 51, United States summary and state data. U.S. Dept. Comm., Washington, DC. Clegg, M. D. 1972. Light and yield aspects of sorghum canopies. p. 279-301. In: N. G. P. Rao and L. R House (eds.), Sorghum in the seventies. Oxford and IBH Publ. Co., New Delhi, India. Coleman, O. H. 1970. Syrup and sugar from sweet sorghum. p. 416-440. In: J. S. Wall and W. M. Ross (eds.), Sorghum production and utilization. AVI., Westport, CT. Coleman, O. H., and B. A. Belcher. 1952. Some responses of sorgo to short photoperiods and variations in temperature. Agron. J. 44:35-39. Collins, J. L., I. C. Yachouh, and I. E. McCarty. 1980. Quality of sorghum-corn syrup blends. Tenn. Farm and Home Science. Agr. Expt. Sta., Univ. Tenn., Knoxville. Dahlberg, T. A., G. C. Peterson, and D. K. Mulitze. 1993. Sorghum pedigree management using Agrobase 14. p. 69. In: Agron. Abstr. A,. Soc. Agron., Madison, WI. Damon, E. G. 1962. The cultivated sorghums of Ethiopia. Ethiopian ColI. Agr. Mech. Arts Expt. Sta. Bul. 6 Day, J. L., R R Duncan, P. L. Raymer, G. R Lovell, D. S. Thompson, H. D. Garrett, and N. Zummo. 1995. Top 76-6: a new sweet sorghum variety for syrup production. Georgia Agr. Expt. Sta. Res. Rpt. 634. deWet, J. M . J. 1978. Systematics and evolution of sorghum sect. sorghum (Gramineae). Am. J. Bot. 65:477-484. deWet, J. M. J., and J. R Harlan. 1971. The origin and domestication of sweet sorghum. Econ. Bot. 25:128-135. deWet, J. M. M., and J. P. Huckabay. 1967. The origin of Sorghum bicolor. II. Distribution and domestication. Evolution 21:787-802. Doggett, H., and K. E. Prasada Rao. 1995. Sorghum. In: Smart, J. and N. W. Simmonds (eds.), Evolution of crop plants. Longman Scientific and Technical. Essex, England. Dube, H.-T., S. K. Dube, G. H. Liang, and S.-D. Kung. 1991. Possible repetitive DNA markers for Eusorghum and Parasorghum and their potential use in examining phylogenetic hypotheses on the origin of Sorghum species. Genome 34:241-250. Easton, J. D. 1972. Photosynthesis and translocation in relation to plant development. p. 214-246. In: N. G. P. Rao and L. R House (eds.), Sorghum in the seventies. Oxford and IBH Publ. Co., New Delhi, India. Ferarris, R, and D. A. Charles-Edwards. 1986a. A comparative analysis of the growth of sweet and forage sorghum crops. I. dry matter production, phenology and morphology. Austral. J. Agr. Res. 37:495-512. Ferarris, R, and D. A. Charles-Edwards. 1986b. A comparative analysis of the growth of sweet and forage sorghum Crops. II. Accumulation of Soluble Carbohydrates and Nitrogen. Austral. J. Agr. Res. 7:513-522. Freeman, J. E. 1970. Development and structure of the sorghum plant and its fruit. p. 28-72. In: J. S. Wall and W. M. Ross (eds.), Sorghum production and utilization. AVI, Westport, CT. Freeman, K. c., D. M. Broadhead, N. Zummo, and F. E. Westbrook. 1986. Sweet sorghum culture and syrup production. U.S. Dept. Agr. Handb. 611.

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Gill, N. T., and K. C. Vear. 1980. Agricultural botany. Duckworth, London. Gould, F. W., and R B. Shaw. 1983. Grass Systematics. Texas A&M Univ. Press. College Station. Hammer, G. 1., and R 1. Vanderlip. 1989. Genotype-by-environment interaction in grain sorghum. I. Effects of temperature on radiation use efficiency. Crop Sci. 29: 370-376.

Hammer, G. 1., R 1. Vanderlip, G. Gibson, 1. J. Wade, R G. Henzell. D. R Younger, J. Warren, and A. B. Dale. 1989. Genotype-by-environment interaction in grain sorghum. II. Effects of temperature and photoperiod on ontogeny. Crop Sci. 29:376-384. Harlan, J. R 1975. Crops and man. Am. Soc. Agron., Madison., WI. Harlan, J. R, and J. M. J. deWet. 1971. Towards a rational classification of cultivated plants. Taxon 20:509-517. Harlan, J. R, and J. M. J. deWet. 1972. A simplified classification of sorghum. Crop Sci. 12:172-176.

Harlan, J. R, J. M. J. deWet, and E. G. Price. 1973. Comparative evolution of cereals. Evolution 27:311-325. Hattendorf, M. J., M. S. Redels, B. Amos, 1. R Stone, and R E. Gwin, JI. 1988. Comparative water use characteristics of six row crops. Agron. J. 80:80-85. Hawker, J. S. 1985. Sucrose. p. 1-51. In: P. M. Dey and R A. Dixon (ed.), Biochemistry of storage carbohydrates in green plants. Academic Press, Orlando, F1. Hills, F. J., R T. Lewellen, and I. O. Skoyen. 1990. Sweet sorghum cultivars for alcohol production. Cal. Agr. 44:14-16. Hipp, B. W., W. R Cowley, and B. A. Smith. 1970. Influence of solar radiation and date of planting on yield of sweet sorghum. Crop Sci. 10:91-92. Hunter, E. 1. 1994. Development, sugar yield and ethanol potential of sweet sorghum. M.S. thesis, Iowa State Univ., Ames. Hunter, E. 1., I. C. Anderson, and D. R Buxton. 1993. Growth, development, and energy potential of sweet sorghum. Agron. Abstr. Am. Soc. Agron, Madison, WI. Kalton, R R 1988. Overview ofthe forage sorghums. p. 1-12. In: D. Wilkinson (ed.), Proc. Forty-third Annual Corn and Sorghum Research Conference. 8-9 Dec., 1988, Chicago, I1. Am. Seed Trade Assoc., Washington, DC. Kidambi, S. P., D. R Krieg, and D. T, Rosenow. 1990. Genetic variation for gas exchange rates in grain sorghum. Plant Physiol. 92:1211-1214. Kresovich, S., and D. M. Broadhead. 1988. Registration of 'Smith' sweet sorghum. Crop Sci. 28:195-196. Krishnaveni, S., T. Balasubramanian, and S. Sadasivam. 1990. Potentiality of sweet sorghum (Sorghum bicolor, Poaceae) for syrup preparation and alcohol production in India. Econ. Bot. 44:355-359. Kuepper, G. 1992. Sweet sorghum: production and processing. Kerr Center for Sustainable Agriculture, Poteau, OK. Lingle, S. E. 1986. Sugar uptake by sweet sorghum stem tissue. Agronomy Abstr. Am. Soc. Agron, Madison, WI. Lingle, S. E. 1987. Sucrose metabolism in the primary culm of sweet sorghum during development. Crop Sci. 27:1214-1219. Lueschen, W. E., D. H. Putnam, B. K. Kanne, and T. R Hoverstad. 1991. Agronomic practices for production of ethanol from sweet sorghum. J. Prod. Agr. 4:619-625. Martin, J. H. 1970. History and classification of sorghum. p. 1-27. In: T. S. Wall and W. M. Ross (eds.), Sorghum production and utilization. AVI, Westport, CT. McBee, G. G., and F. R Miller. 1982. Carbohydrates in sorghum culms as influenced by cultivars, spacing, and maturity over a diurnal period. Crop Sci. 22:381-385.

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McBee, G. G., and F. R Miller. 1990. Carbohydrate and lignin partitioning in sorghum stems and blades. Agron. J. 82:687-690. McBee, G. G., R M. Waskom, III, F. R Miller, and R A. Creelman. 1983. Effect of senescence and nonsenescence on carbohydrates on sorghum during late kernel maturity states. Crop Sci. 23:372-376. McCree, K. J., c. K. Fernandez, and R Ferraz de Oliviera. 1990. Visualizing interactions of water stress responses with a whole-plant simulation model. Crop Sci. 30:294-300. McGowan, M., H. M. Taylor, and J. Willingham. 1991. Influence ofrow spacing on growth, light, and water use by sorghum. J. Agr. Sci. 116:329-339. Miller, F. R, and G. G. McBee. 1993. Genetics and management of physiologic systems of sorghum for biomass production. Biomass Bioenergy 5:41-49. Nan, 1., and J. Ma. 1989. Research on sweet sorghum and its synthetic applications. Biomass 20:129-139. National Academy of Science. 1996. Lost crops of Africa. p. 195-214. Nat. Acad. Press, Washington, DC. NSSPPA, 1994. National Sweet Sorghum Producers and Processors Association Newsletter, 9(1):1-3. Prine, G. M., 1. S. Dunavin, B. J. Brecke, R 1. Stanley, P. Mislevy, R S. Kalmbacher, and D. R Hensel. 1988. Model crop systems: Sorghum, Napiergrass. p. 83-102. In: W. H. Smith and J. R Frank (eds.), Methane from biomass: a systems approach. Elsevier Applied Science, New York. Putnam, D. H., W. K Lueschen, B. K. Kanne, and T. R Haverstad. 1991. A comparison of sweet sorghum cultivars and maize for ethanol production. J. Prod. Agr. 4:377-381. Quinby, J. R 1967. The maturity genes of sorghum. Adv Agron 19:267-305. Quinby, J. R, and K. F. Schertz. 1970. Sorghum genetics, breeding, and hybrid seed production. p. 73-11. In: J. S. Wall and W. M. Ross (eds.), Sorghum production and utilization. AVI, Westport, CT. Rao, K. K P., and D. S. Murty. 1981. Sorghum for special uses. p. 129-134. In: J. V. Mertin (ed.), Proc. Int. Symp. on Sorghum Grain Quality, 18-31 Oct. 1981, Patancheru, India. ICRISAT, Pantancheru, India. Schaffert, R K, and 1. M. Gourley. 1982. Sorghum as an energy source. p. 605-623. In: J. V. Mertin (ed.), Sorghum in the eighties. Proc. Int. Symp. on Sorghum, 2-7 Nov. 1981, Patancheru, India. ICRISAT. Pakancheru, A.P., India. Schertz, K. F., and D. R. Pring. 1982. Cytoplasmic sterility systems in sorghum. p. 373-384. In: J. V. Mertin (ed.), Sorghum in the eighties: Proc. Int. Sym. on sorghum, 2-7 Nov. 1981, Patancheru, India. ICRISAT, Patancheru, A.P., India. Shaffer, S. D., B. M. Jenkins, D. 1. Brink, M. M. Merriman, B. Mouser, M. 1. Campbell, C. Frate, and J. Schierer. 1992. Agronomic and economic potential of sweet sorghum and kenaf. p. 7-16. In: J. S. Cundiff (ed.), Liquid fuels from renewable resources. Am. Soc. Agr. Engr., St. Joseph, MI. Shih, S. F. 1986. Evapotranspiration, water-use efficiency, and water table studies of sweet sorghum. Trans. Am. Soc. Agr. Engr. 29:767-773. Shih, S. F., G. J. Gascho, and G. S. Rahi. 1981. Modeling biomass production of sweet sorghum. Agron. J. 73:1027-1032. Sieglinger, J. B., and J. H. Martin. 1939. Tillering ability of sorghum varieties. J. Am. Soc. Agron. 39:475-488. Singh, R, and B. Asthir. 1988. Import of sucrose and its transformation to starch in the developing sorghum caryopsis. Physiol. Plant. 74:58-65. Smith, G. A., and D. R. Buxton. 1993. Temperate zone sweet sorghum ethanol production potential. Biores. Tech. 43:71-75.

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Smith, G. A., M. O. Bagby, R. T. Lewellan, D. 1. Doney, P. H. Moore, F. J. Hills, 1. G. Campbell, G. J. Hogaboam, and K. Freeman. 1987. Evaluation of sweet sorghum for fermentable sugar production potential. Crop Sci. 27:788-793. Snowden, J. D. 1936. The cultivated races of sorghum. Adlard and Son, London. Stephens, J. c., F. R. Miller, and D. T. Rosenow. 1967. Conversion of alien sorghums to early combine genotypes. Crop Sci. 7:396. Sung, S.-J. S., D.-O. Xu, and C. C. Black. 1989. Identification of actively filling sucrose sinks. Plant Physiol. 89:1117-1121. Tarpley, 1., S. E. Lingle, D. M. Vietor, D. 1. Andrews, and F. R. Miller. 1994. Enzymatic control of nonstructural carbohydrate concentrations in stems and panicles of sorghum. Crop Sci. 33:446-452. Vander Hart, P. 1992. Sweet memories: sorghum making. Lower Grove Books, Pella, IA. Vanderlip, R. 1. 1972. How a sorghum plant develops. Cooperative Extension Service, Contribution 1203. Kansas State Univ., Manhattan. Ventre, E. K., S. Byall, and J. 1. Catlatt. 1948. Sucrose, dextrose, and levulose content of some domestic varieties of sorgo at different stages of maturity. J. Agr. Res. 76:145-151. Vietor, D. M., and F. R. Miller. 1990. Assimilation, partitioning, and nonstructural carbohydrates in sweet compared with grain sorghum. Crop Sci. 30:1109-1115. Wall, J. S., and C. W. Blessin. 1970. Composition of sorghum plant and grain. p. 118-166. In: J. S. Wall and W. M. Ross (eds.), Sorghum production and utilization. AVI, Westport, CT. Wiedenfeld, R. P. 1984. Nutrient requirements and use efficiency by sweet sorghum. Energy Agr. 3:49-59. Wigginton, K 1975. Foxfire 3. Anchor Press, Garden City, NY. Wright, M. K, F. C. Read, J. J. Massey, and J. P. Clark. 1976. Development ofa communitysized sorghum syrup plant. ASAE Paper no. 76-6009. Am. Soc. Agr. Engr., St. Joseph, M1.

4

Deficit Irrigation in Deciduous Orchards* M. H. Behboudian Department of Plant Science Massey University Palmerston North, New Zealand T. M. Mills Environment Group HortResearch Palmerston North New Zealand

1. Introduction II. The Concept of Deficit Irrigation A. Early-Season Deficit Irrigation B. Late-Season Deficit Irrigation C. Deficit Irrigation Throughout the Fruit Growing Season D. Postharvest Deficit Irrigation III. Physiology of Deficit Irrigation A. Vegetative Effects 1. Shoot Growth 2. Leaf Area 3. Trunk Growth 4. Root Growth B. Yield Effects C. Fruit Quality Effects IV. Establishment of Irrigation Schedules for Deficit Irrigation V. Future Prospects Literature Cited

*We thank Drs. H. W. Caspari, B. E. Clothier, and B. R. MacKay for their valuable comments.


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M. H. BEHBOUDIAN AND T. M. MILLS

I. INTRODUCTION

There is an urgent need to identify and adopt effective irrigation management strategies. Water, the most precious environmental resource, is increasingly in demand mainly because of population growth, increased industrialization, and deteriorating water quality. As irrigation of agricultural lands accounts for over 85% of water usage worldwide (van Schilfgaarde 1994), even a relatively minor reduction in irrigation water use could substantially increase the water available for municipal and industrial purposes. Managing demand rather than trying to develop new supplies seems to be a realistic goal for irrigated agriculture. Deficit irrigation (DI) is one option for reducing water requirements. Deficit irrigation is a system of managing soil water supply to impose periods of predetermined plant or soil water deficit that can result in some economic benefit. It involves giving less water to the plant than the prevailing evapotranspiration (ET) demand at selected times during the growing season. Deficit irrigation is a method originally designed for vegetative growth control (Chalmers et al. 1981); it can produce significant benefits under favorable circumstances (Hargreaves and Samani 1984). Conditions, however, must be right for higher economic returns upon application of Dr. In addition to saving irrigation expenses, fruit yield was higher with DI of 'French' prune in deep soil and under mild and moderate DI in a shallow soil. However, for severe DI in shallow soil the economic return was lower than the control (Lampinen et al. 1995). Deficit irrigation may also have a positive impact on environmental quality. While well-drained soils are suitable for the establishment of deciduous orchards, they also tend to facilitate the leaching of nutrients and pesticides into groundwater. Of primary concern is drainage beyond the root zone of nitrates, pesticides, and dissolved mineral salts (Tanji 1993). Deficit irrigation in conjunction with a reduced use of pesticides and nutrients may help prevent groundwater contamination and it will adhere to the environmental protection legislation that exists in some countries (Tanji 1993). Deficit irrigation is expected to be more successful in dry than in humid areas because in the latter rain can interfere with achieving an intended low plant/soil water status in commercial production. Soil covers, used in New Zealand (Durand 1990; Mills et al. 1994), can exclude rain for research purposes, but they are not practical for commercial use. The term regulated deficit irrigation (RDI) is normally used in the literature to denote DI of trees early in the season, before rapid fruit growth starts. Late-season RDI-which refers to the application of RDI before harvest with a duration depending on the purpose, species, and envi-

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ronmental conditions-has also been used in some occasions to improve fruit quality (Mills et al. 1994; Mills et al. 1996a). The term deficit irrigation is used by some authors to mean "no irrigation." We have taken DI to be synonymous with RDI because it implies partial replacement of the evapotranspiration needs of plants for achieving a predetermined plant/soil water deficit. The concept ofRDI was initially studied in Australia and was used as a management strategy to control vigor in high-density plantings of 'Golden Queen', a late season peach (Chalmers et al. 1981; Mitchell and Chalmers 1982), and 'Bartlett' pear (Mitchell et al. 1984). In these experiments, controlled water deficit was established in the plant during the period of rapid shoot and slow fruit growth. During the period of RDI, trees were irrigated at a rate lower than the evapotranspiration with sufficient water being made available to the plant just as the fruit started their rapid growth phase. If applied as designed, RDI did not have any negative effects on fruit growth and final yield, but was able to decrease shoot growth and reduce tree size. The concept of RDI was subsequently explored in countries other than Australia. Detailed studies on the physiology of fruit trees, especially peach, under RDI have been carried out in California by applying RDI after harvest to early ripening cultivars (Girona et al. 1993). There are no reviews on this subject with the exception of that by Chalmers (1989), who briefly reviewed the physiology and management ofRDI in apple, peach, and pear. II. THE CONCEPT OF DEFICIT IRRIGATION The impact of DI is strongly dependent on the timing of the water deficit because most events in plant development are seasonal, periodic, or both. Deciduous fruit crops are active for approximately 9 months out of 12, with the plant entering dormancy over the winter months so that plant water use is minimal, although root growth continues in winter (Kramer and Boyer 1995). It is during the active growth phase that DI has the most influence on the performance of the crop. In the following sections, examples of DI experiments in which fruit yield and quality have been maintained are cited in relation to seasonal timing and resulting savings in water. They relate to a wide range of climatic and soil regions. Comparison between studies becomes ever more difficult because various authors have used different parameters to assess both soil or plant-water status. Soil-water status could only be meaningfully compared between studies if expressed in terms of soil-water

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potential, which is rarely reported because it is difficult to measure in the appropriate range of dryness. Plant-water status has mainly been measured as leaf-water potential employing the Scholander pressure chamber. This allows direct comparison. Because of effective stomatal control over transpiration, the midday leaf-water potential between trees in humid and in dry areas could be similar (Jones et al. 1985). For this reason, we have also included the predawn leaf-water potential values wherever available. A. Early-Season Deficit Irrigation Water deficit during flowering is likely to inhibit fertilization (Hsiao 1993). Powell (1974) reported reduced fruit set and increased fruit abscision when water deficit was induced during flowering in apple. However, early-season DI applied following the completion of flowering and fruit set could result in the same yield in deficit-irrigated plants as in well-watered plants with considerable saving of water. An experiment by Li et al. (1989) on 'Merrill Sundance' peach in the Rhone Valley of France showed that DI applied at fruit growth stages I [up to 50 days after full bloom (DAFB)], II (50-99 DAFB), and their combination did not reduce yield and resulted in water saving of, respectively, 553, 561, and 1114 m 3 /ha. The soil was sandy alluvial and the control treatment was irrigated when a soil-water potential of about -60 kPa was reached. No irrigation was done during stage I, and for stage II the irrigation was a third of the control. The benefits of early-season DI on 'Bartlett' pear was demonstrated in a five-year study in Victoria, Australia, by Mitchell et al. (1989) whose treatments were replacement of 23%,46%, and 92% of evaporation from the planting square (Eps), as measured by U.S. Class A pan. The DI periods lasted approximately 70 days from October to early December. Dawn leaf-water potential was -0.24 and -0.29 MPa in the 92% and 23% Eps, respectively. Deficit irrigation saved 2 megaliters of water/ha per year, and the yield increased in the two drier treatments compared to 92 % Eps. Fruit number also tended to be greater in the 23% and 46% Eps treatments in all years. Weight of summer pruning was positively and linearly related to the level of irrigation in each year including a relatively wet year. DI resulted in less pruning. The degree of this response was related to net evaporation during the rapid shoot growth (Fig. 4.1; Mitchell et al. 1989). The feasibility of early-season DI for controlling vegetative growth and for saving water in apple production is evidenced in the study of Ebel et al. (1995) on 'Redspur Delicious' in the semiarid environment of Prosser, Washington. Average annual precipitation in this area is 190 mm, of


109

.--

•

8

0.23 Eps

~

c

60

y = 8.96 + 0.157x

r = 0.94

C

*

•

:J

8

I.-

a.

E l.-

40

E

.

:J tJ)

C Q) tJ)

ro

20

0.46 Eps

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l.-

t) Q)

y=8.13+0.118x r=0.74(ns)

o

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!

200

Net Evaporation (evap.

300

rain) mm

Fig. 4.1. Effects of irrigation level [replacing 23% (0.23 Eps) and 46% (0.46 Eps) of evapotranspiration] and net evaporation during Oct. and Nov. (Southern Hemisphere) on the percent decrease in weight of summer pruning relative to 92% replacement of evapotranspiration treatment in each of five years (numbers 8 to 12 indicate tree age) for 'Bartlett' pear trees (adapted from Mitchell et al. 1989).

which 50 mm falls during May through September. Total evaporation from a U.S. class A pan at the experimental site was approximately 800 mm from June to September. There were four treatments: furrow control (FC), trickle control (TC), DI/microsprinkler (DIM), and DIItrickle (DIT). In FC, the field was irrigated every two weeks and brought to field capacity; in TC, 100% of ET (estimated from pan evaporation and the use of a crop factor) was replaced by irrigation; and in DIM and DIT, water was withheld until terminal buds set and then 100% of ET was replaced by irrigation. At the end of the DI period, the stem-water potentials were -2.09, -1.89, -1.14, and -0.89 MPa in DIT, DIM, TC, and FC, respectively. The last two values are significantly higher than the first two. The DI treatments increased yield efficiency (yield/trunk cross-sectional area) and resulted in saving of water by 230 mm when comparing DIT with TC, and by 105 mm when comparing DIM with FC. There are examples of the usefulness of early-season DI in other species. In New Zealand, which has a humid environment, a lysimeter study by Caspari et al. (1994) on 'Hosui' Asian pear showed that early

110


DI trees used 20% less water. The DI treatment lasted from 42 to 115 DAFB and the trees were irrigated at 33% of the control. The predawn and midday leaf-water potential of the DI trees were, respectively, -0.3 and -2.3 MPa, compared to -0.1 and -1.4 MPa for the controls. Deficit irrigation reduced shoot extension and summer pruning weights, whereas winter pruning weights were not different between treatments. Except for the final week of the DI, fruit growth was not reduced and DI fruit grew faster than the control during the first week after rewatering. Final fruit size and yield were not different between treatments. On 'Chardonnay' grape at Barooga, Australia, Goodwin and Jerie (1989) applied DI for a period of 110 days from bud burst to six weeks after flowering. Treatmentsconsisted of replacement ofET by 0%,57.5%, and 100%. During the flowering, soil-matric potential decreased from -0.12 to -0.18 MPa around the nonirrigated vines at a rate of -0.004 MPa/d. By the end ofthe DI period, the average soil-matric potential was -0.31 MPa in the nonirrigated plots. There was no loss in yield, berry number or berry fresh weight, dry weight, pH, total titratable acidity, or sugar concentration. Over the six-week period, 0.6 megaliters of water was saved per hectare. Early-season DI may decrease some fruit disorders (Brun et al. 1985; Lotter et al. 1985). In some cases, however, it increases the incidence of disorders such as flesh spot decay in 'Nijisseiki' Asian pear (Behboudian and Lawes 1994). Early-season water stress during fruit cell division may reduce cell number (Hsiao 1973) and thus the final fruit size. Nevertheless, early-season DI can be used as an effective management tool if soilwater holding capacity is low enough to allow physiological water deficit to develop sufficiently early to have a useful horticultural effect. B. Late-Season Deficit Irrigation This refers to a deficit that is imposed during the later stages of fruit growth prior to harvest. A late-season deficit did not reduce shoot growth or total leaf area, but did limit the structural size of the tree by reducing radial trunk growth in 'Braeburn' apple (Mills et al. 1996b) and in 'Hosui' Asian pear (Caspari 1993). Exposing apple fruit trees to a late water deficit may reduce fruit yield (Lotter et al. 1985), although not always (Irving and Drost 1987; Mills et al. 1996b). In the study of Mills et al. (1996b), the late-season DI was applied in a glasshouse and lasted for 78 days prior to harvest at 183 DAFB. The mean glasshouse temperature was 22°C, and potential evaporation was 2.5 mm/d. Predawn leaf water potential decreased from -0.29 MPa in well-watered plants to -0.48 MPa in deficit-irrigated plants. The corresponding volumetric moisture content in the soil declined from 0.35 to 0.17 m 3 /m 3 , respec-

4. DEFICIT IRRIGATION IN DECIDUOUS ORCHARDS

111

tively. Deficit irrigation resulted in water saving of at least 156 lItree. Completely cutting off irrigation, which is not strictly regulated DI, has also been practiced in some cases. An example is the four-year study on French prune in the southern San Joaquin Valley, California, reported by Goldhamer et al. (1994). The irrigation cutoff was done from 12 to 45 days before harvest on a deep, well-drained Foster fine sandy loam. Predawn and midday leaf-water potential for the 45-day cutoff were -1.6 and -3.1 MPa, respectively. The corresponding values for the 12-day cutoff were -0.9 and -2.3 MPa. Except for the 45-day cutoff in the last year, the yield was generally increased under these cutoffs. Soluble solids tended to be higher and dry ratios (fresh fruit wt/dry fruit wt) lower with early cutoffs. Reduction of fruit size, which is a concern in late-season DI, may constitute an advantage in some instances. Examples could be given for large peach (Li et al. 1989) and pear (Kappel et al. 1995) cultivars for which size reduction enhances market value, and also for grape berries in which size reduction improves wine quality (Freeman 1983; Matthews and Anderson 1988). However, this is not to recommend the use of DI as a deliberate mechanism of reducing fruit size. Fruit composition and some quality attributes are modified under reduced water status late in the season in apple (Mills et al. 1994; 1996a) and in peach (Li et al. 1989). Desirable fruit quality changes make late DI advantageous in certain situations. However, more information is required regarding particular varieties before it can be recommended.

c.

DeficitIrrigation Throughout the Fruit Growing Season

The effect of whole-season DI in a glasshouse and in the field was determined in 'Braeburn' apples in New Zealand. Predawn leaf-water potential decreased from -0.31 to -0.41 MPa in the glasshouse and from -0.35 to -0.66 MPa in the field. The corresponding midday values decreased from -1.5 to -2.0 and from -1.26 to -1.78 MPa, respectively. Fruit size was significantly lower in deficit-irrigated trees than in control trees for the glasshouse experiment (Mills et al. 1996b) but not in the field (Fig. 4.2; Kilili et al. 1996). Although the development of stress will depend on the environment, it seems prudent not to recommend an entire season DI as a management tool. This would be especially true if DI imposes water stress during flowering and fruit set. D. Postharvest Deficit Irrigation

In most deciduous fruit crops, especially early maturing cultivars, a significant amount of tree growth occurs after harvest. Water deficit at this


112

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Days after full bloom Fig. 4.2. Effect oftiming of deficit irrigation on fruit size in 'Braeburn' apples. Compared to well-watered controls, fruit size was not significantly reduced in any of the deficitirrigation treatments. For each treatment, every point is the average of 18 fruit from 9 trees. Separate bars are pooled standard errors of the means and the arrow indicates the time early-deficit irrigation stopped and late-deficit irrigation started. The soil moisture in the deficit-irrigated plots was significantly lower than that of the control (adapted from KiWi et al. 1996).

time has been shown to reduce the pruning requirements of peach, while increasing flower density the following season, but unfortunately also increasing the occurrence of double fruits (Johnsonet al. 1992). This experiment was carried out in Parlier, California, on a fine sandy loam overlying a dense hardpan at a depth of between 270 to 300 mm. Mean annual rainfall during the experimental period (1983-86) was 260 mm, with no significant rainfall during the postharvest period between midJune and mid-October. The treatments were: "control," which was irrigated 100 to 150 mm at two to three week intervals; "medium dry," which was irrigated once with 200 to 300 mm at about 50 days after harvest, and "dry," which was not irrigated throughout the postharvest period. The upper layers of soil began to dry out in the deficit treatments and water extraction occurred at increasingly greater depths. Postharvest water deficit reduced radial trunk growth more than shoot growth, as


113

shoot growth was predominant during spring. A postharvest water deficit may be of benefit in peach cultivars with low flower number and may also help control tree vigor. It also may make the tree more winter hardy by reducing late-season growth (Westwood 19S5). III. PHYSIOLOGY OF DEFICIT IRRIGATION

Deciduous orchard trees are complex perennials which respond differently to water deficit depending on their physiological stage (Landsberg and Jones 19S1). Most events in plant development occur periodically and are sensitive to plant-water status during active periods (Chalmers 19S9). The physiological principles of DI reviewed by Caspari (1993) include the functional equilibrium between roots and shoots, the phenological separation of shoot and fruit growth, and the ability of fruit to restart rapid growth once irrigation is resumed. A functional equilibrium exists between the growth of roots and shoots (Richards and Rowe 1977). In peach trees, for example, in a given environment there is a constant relationship between the relative growth rates of the top and of the roots even though the allocation of dry matter toward the above- and below-ground portions of the tree changes markedly (Chalmers and van den Ende 1975). This suggests that a particular ratio of roots to shoots is developed in a given environment. Restricting root development in fully grown trees by orchard management techniques can thus be used to reduce vegetative vigor, which has a secondary benefit of increasing flower production, bloom density, and allocation of dry matter to fruit (Richards 19S5). Root volume can be restricted by management techniques such as planting density (Chalmers et al. 19S4), type of rootstock (Chalmers 19S9), and irrigation system (Proebsting et al. 1977; Mitchell and Chalmers 19S3). By assuming that roots in dry soil are physiologically inactive (Proebsting et al. 19S9) and will not grow into dry soil, DI can reduce the effective root volume and lead to less vigorous and more fruitful trees (Richards 19S5). Water deficit in the root zone, once established and maintained until the start of rapid fruit growth, will primarily affect the development of shoots (Chalmers 19S9). As the fruit in this early growth stage (early period of cell expansion) have a lower assimilate demand and are less sensitive to water stress than the shoots, water deficit can significantly reduce the shoot growth with little or no reduction in fruit growth (Mitchell et al. 19S4). Deficit irrigation is complementary to other management techniques that restrict the root system development, including irrigation system or planting density. Mitchell et al. (19S9) found that increases in fruit yield


114

in response to DI tended to be higher at closer spacing, confirming that DI is more efficient where root growth is already suppressed by other mechanisms. The phenological separation of shoot and fruit growth that occurs in certain cultivars of some deciduous fruit crops (Fig. 4.3; Chalmers et al. 1985) is another important factor allowing the application of Dr. This separation allows the timely application of DI to check undesired vegetative growth through a reduction in plant-water status. In addition, different organs, tissues, and processes of the tree can vary in their sensitivity to reduced plant-water status. Processes of photosynthesis and translocation of assimilates are not suppressed at water potentials that inhibit cell expansion, which is particularly sensitive to water stress (Hsiao et al. 1976). Fruit are thought to be less affected by water deficit than shoots because fruit are stronger sinks and accumulate large quantities of soluble solids over the season (Chalmers 1989). This should, therefore, make feasible the use of DI in species whose shoot and fruit growth have more overlaps than shown for peach and pear in Fig. 4.3. Following return to full irrigation at the start of rapid fruit expansion, previously deficit-irrigated fruit may briefly grow at a faster rate than well-watered fruit as shown for peach (Mitchell and Chalmers 1982) and

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Month (Southern Hem isphere) Fig. 4.3. The cumulative growth of annual shoots and fruit of a late ripening peach, 'Golden Queen,' and 'Bartlett' pears expressed as a proportion ofthe total seasonal growth by those organs (adapted from Chalmers et al. 1985). At the completion of shoot growth (100%), fruit growth is approximately 25% complete in peach and 27% complete in pear.


115

pear (Jerie et al. 1989). This compensatory growth has been attributed to active osmotic adjustment during DI (Chalmers 1989). However, there is scant evidence of osmotic adjustment in deficit-irrigated fruit in the literature. Whatever the mechanisms of compensatory growth, whenever it happens, it helps to compensate for reduced fruit growth during water deficit. A. Vegetative Effects 1. Shoot Growth. The importance of controlling tree vigor in perennial fruit crops is well established (Chalmers et al. 1985). At the beginning of the growing season, fruit growth follows shoot growth in late-season peach, pear (Chalmers 1989), and apple (Lotter et al. 1985). The reduction in shoot growth under DI is predominantly due to its earlier cessation (Mitchell et al. 1986; Irving and Drost 1987). Controlling tree vigor under DI reduced the summer pruning requirements in late-season peach (Chalmers et al. 1981; Mitchell and Chalmers 1982), pear (Chalmers 1989), and apple (Durand 1990). Deficit irrigation decreased summer prunings of pear for each year of a five-year study in Australia (Fig. 4.1). Aside from the economic benefit of reduced pruning costs, a reduction in vegetative growth may reduce the competition for photoassimilates between fruit and vegetative parts and may, therefore, enhance fruit size. Less vegetative growth also allows better light penetration into the canopy, thus improving fruit color development (Westwood 1988; Lancaster 1992), and ensures more effective spray coverage. 2. Leaf Area. Regulation of leaf area plays an important role in the adaptation of fruit crops to water deficit (Jones et al. 1985; Lakso 1985). Reduced leaf area under water stress is due to several factors including a reduction in shoot growth (Lotter et al. 1985), lower total leaf number (Lakso 1983), and reduced leaf area expansion (Hsiao 1993). The latter is due to the sensitivity of cell growth, namely cell division and cell expansion, to reduced plant-water status (Hsiao 1973). A reduction in leaf area index (LAI), a measure of the total leaf area of a plant or plants divided by the land area covered, was observed in peach under DI (Boland et al. 1993). In apple and pear, a decrease in LAI may result in a reduction in the interception of photosynthetically active radiation (PAR) which in turn could reduce total carbon assimilation and total dry-matter production (Hsiao 1993). Thus, a reduction in intercepted PAR may lower carbon assimilation of fruit trees. Other factors such as reduced stomatal conductance of apple (Mills et al. 1994; 1996b), peach (Boland et al. 1993), Asian pear (Caspari et al. 1994), and European pear

116


(Brun et al. 1985) under water deficit may also contribute to reduced carbon assimilation. Hsiao (1973) and Landsberg and Jones (1981) provide a more comprehensive discussion of the influence of water stress on stomatal response, transpiration, and carbon assimilation. Aside from lower leaf area expansion, leaf area may also decrease as an adaptive response of the plant to reduced water status. Adaptations include leaf folding about the midrib (Lakso 1983) and leaf abscission in extreme cases of water deficit (Hsiao 1993; Behboudian et al. 1994). 3. Trunk Growth. Water deficit tends to reduce trunk growth in apple (Iancu 1985; Irving and Drost 1987), peach (Chalmers et al. 1985; Boland et al. 1993), and pear (Mitchell et al. 1989). This is associated with reduced total tree size. Trunk cross-sectional area is linearly related to the above-ground weight of the tree (Westwood and Roberts 1970), unless complicated by major pruning or training. Unlike shoot growth, trunk growth continues throughout the season, albeit at a slower rate (Taerum 1964; Johnson et al. 1992); therefore, severe water deficit at any time of the season may reduce trunk growth (Mills et al. 1996b). As with most organs in the plant, the trunk shows diurnal fluctuations in size (Landsberg and Jones 1981; Li and Huguet 1990). Water deficit increases the diurnal contractions in the stem diameter (Li and Huguet 1990). Measurement of these diurnal contractions provides information on the water status of the plant, and irrigation may be scheduled accordingly. Some researchers have used radial trunk growth as an indicator of irrigation requirements (Taerum 1964). 4. Root Growth. Water stress generally increases the proportion of new

dry matter consigned to the roots in preference to the shoots. This is possibly because roots are exposed to less severe water stress than shoots (Kramer 1988). The absolute amount of root growth may, however, be decreased under water deficit (Landsberg and Jones 1981). Reduced root growth of apple trees under DI was reported by Cripps (1971), who also observed a general change in the pattern of the root system. Studies by Goode and Hyrycz (1964) on mature apple trees indicated that although the total weight of roots was not different between soil moisture treatments, significantly more roots existed in the top 15 cm of soil in trees that were fully watered. A change in the configuration of root growth may well indicate adaptation of the roots in trees that are exposed to water deficit. An increase in rooting depth and length density in response to water deficit was considered a major adaptive mechanism for improving water uptake (Turner 1986). Under water-deficit conditions, an increase in the root to shoot ratio may also occur, as shoot growth is generally


117

reduced more than root growth (Kramer and Boyer 1995). Increased root to shoot ratios ensure better water supply from the root to the existing shoots, making the plant more tolerant of soil-moisture deficit (Syvertsen 1985). Chalmers et al. (1981) reported that DI used in conjunction with high peach tree density (1m by 2m spacing) reduced shoot growth due to root competition and enhanced the dwarfing effect. Mandre et al. (1995) hypothesized that a physiological signal originating in the roots of peach trees with confined root area reduces vegetative growth without influencing fruit growth. Proebsting et al. (1989) showed that root restriction, by reduction of soil volume, has a similar influence on the above-ground portion of the peach as does water deficit. Similarly, Girona et al. (1993) observed that only a mild water stress develops in peach under DI in deep soil. By removing root confinement in peach, Proebsting et al. (1989) observed no reduction in flowering under DI, whereas under conditions of root restriction DI seriously reduced flowering of peach the following year. In peach, a certain size of shoot is needed for flower bud development. A combination of root restriction and DI is a severe enough stress to decrease shoot growth below the level needed for flower bud formation (Faust 1989). A method of root growth restriction in peach was examined by Glenn and Welker (1989) by providing competition from tall fescue sod. The presence of sod reduced the root length density (em root length/cm 3 soil) of fine roots «1 mm in diameter) beneath the sod and in the transition zone between the sod and the tree. However, if grasses are to be used in establishment of DI, considerations should be given to their competition for nutrients and to their possible allelopathic potential.

B. Yield Effects The impact of any management strategy on the performance of horticultural crops must be analyzed in terms of marketable yield. In deciduous fruit crops, marketable yield is dependent on fruit number, size, and quality. Fruit number depends on the number of initiated flowers and on final fruit set, but the effect of water deficit on these processes is contradictory. An increase in flowering in the season subsequent to water deficits has been observed in pear (Mitchell et al. 1984; Raese et al. 1982) and peach (Chalmers et al. 1985). Degman et al. (1932) noted an increase in bloom for apple following a dry season during which water stress developed, although Mills et al. (1994) found no significant increase in flower number in the spring following late-season DI in apple. Thus, it would appear that the timing of water deficit is important. Proebsting et al. (1977) observed that in young 'Delicious' apple

118


trees, flower number and fruit set were greater under trickle irrigation than under sprinkler irrigation. The former irrigation system provides less water than the latter. Improved number of fruits remaining after postbloom drop was also observed in peach exposed to water stress (Li et al. 1989). In contrast, Caspari et al. (1994) found a reduction in return bloom on Asian pear under early-season DI, but with no significant reduction under late-season DI. This is in agreement with Brun et al. (1985) who observed a reduction in return bloom and fruit set of pear following a dry treatment during the previous season. Powell (1974) also noted reduced fruit set in apple and increased fruitlet abscission or June drop in droughted compared with irrigated trees. Severe water stress at the time of pollination is also likely to inhibit fertilization (Hsia61993), although a deficit is unlikely to occur at that time. Another important consideration with many perennial fruit crops is the tendency for biennial bearing. A stimulation in flowering following DI treatments can help counteract the biennial bearing tendencies of some peach and pear cultivars by increasing yield in an off year (Chalmers et al. 1985). It is clear that although fruit number and return bloom may be influenced by DI, the outcome is strongly dependent on the level and timing of the deficit imposed and on tree species. Fruit size under DI management was initially reduced in peach (Mitchell and Chalmers 1982) and pear (Chalmers et al. 1986), but once full irrigation resumed, fruit growth was stimulated and the final yield equaled that of fully irrigated treatments. In some cases, the final yield was actually increased (Chalmers et al. 1986; Mitchell et al. 1986; Mitchell et al. 1989). Similar responses of apple under DI treatments were also reported by Durand (1990) in a humid region of New Zealand. Chalmers et al. (1986) postulated that pear fruit osmoregulates to maintain and/ or~'9crease growth at the expense of inhibited vegetative growth when DI redlces leaf-water potential in early season to values approaching -0.6 MPa at dawn. Behboudian et al. (1994) showed osmotic adjustment in Asian pear fruit for early-season DI but not for late-season DI. Fruit from early-season DI increased growth after rewatering, while growth of late-season DI fruit was not affected. It is important to note that a reduction in fruit size as a result of DI may not always be a disadvantage. For example, in peach cultivars with extra large fruit, such as 'Merrill Sundance', a slight reduction of fruit size does not diminish their market value (Li et a1. 1989). In addition, large apple fruit are often more prone to mineral imbalances and the development of storage disorders (Guelfat'Reich et al. 1974).


119

C. Fruit Quality Effects

Consumer preference defines fruit quality (Kingston 1991), and flavor, texture, and appearance play important roles in defining quality in most fruits. Of paramount importance in determining fruit quality is the maturity of fruit for eating, commonly termed commercial maturity (Kingston 1991). Deficit irrigation may advance fruit maturity in apple (Guelfat'Reich et al. 1974; Ebel et al. 1993; Mills et al. 1994) and pear (Raese et al. 1982). Thus, fruit quality changes are expected under DI. Fruit firmness or texture is very important in apple and is strongly influenced by fruit maturity, with firmness decreasing in apple and pear as the fruit ripen (Kingston 1991). Fruit firmness is also influenced by fruit size (Ebel et al. 1993), with smaller fruit being generally firmer than large fruit due to a higher cellular density. Theoretically, treatments that decrease fruit size should increase firmness. This is not borne out uniformly by existing data. Drake et al. (1981) indicated that apple slices were softer from trees supplied with less water. Mills et al. (1994) observed a reduction in firmness in apple fruit from trees with reduced water status. Pear has softer fruit under reduced irrigation (Raese et al. 1982). These findings indicate an increased maturity in fruit from drier treatments, or possibly low turgor in these fruit cells. In contrast, other researchers have shown that apple from nonirrigated plots were firmer than those from irrigated plots (Haller and Harding 1937; Guelfat'Reich et al. 1974; Assaf et al. 1975; Guelfat'Reich and Ben-Arie 1979). Assaf et al. (1975) indicated that fruit from trees under water deficit were smaller than those from control trees, which may account for the observed increase in fruit firmness. Reduced firmness of fruit from well-irrigated trees may be the result of an inflation of cell size and an increase in the fragility of cell walls (Guelfat'Reich and Ben-Arie 1979). Caspari et al. (1996) found no difference in fruit firmness of Asian pear from wellwatered, early-DI, or late-DI treatments at similar fruit size. In conclusion, the influence of irrigation on fruit firmness is unclear and appears dependent on other factors; it warrants further investigation. In many previous studies, the relationship between fruit firmness and fruit size has not been sufficiently considered. Total soluble solids (TSS) and acidity have a marked influence on the sensory quality of apple fruit (Ackermann et al. 1992). Numerous authors report a significant increase in TSS under DI in apple (Ebel et al. 1993; Mills et al. 1994, 1996a), peach (Li et al. 1989; Crisosto et al. 1994), and pear (Raese et al. 1982). In contrast, early-season DI reduced TSS levels in European pear (Chalmers et al. 1985) or had no effect on Asian pear

120


(Behboudian and Lawes 1994; Caspari et al. 1996), or peach (Li et al. 1989). Chalmers et al. (1985) suggested that because full irrigation is supplied to trees during the later stages of growth under DI conditions, the increased fruit-water content of previously stressed fruit may dilute soluble solids, thus giving a lower TSS value. Layne et al. (1981) reported no change in the acidity of peach under DI, but information on titratable acidity in apple is conflicting. Mills et al. (1994, 1996a) found an increase in acidity under reduced water status, whereas Drake et al. (1981) showed an opposite effect. Irving and Drost (1987) observed no change between irrigated and deficit-irrigated treatments. Red coloration in apple is due to anthocyanins (Lancaster 1992) and is stimulated by light and cool temperatures. Mills et al. (1994) observed increased development of red pigmentation of fruit equally well-exposed to light from trees with a lowered water status. They suggested that this may have been due to the advanced accumulation of fruit sugars which play an important role in anthocyanin development. Westwood (1988) also noted that factors increasing carbohydrate levels of fruit preharvest tend to increase anthocyanin pigment development. Apple cultivars that ripen to a green or yellow color, such as 'Granny Smith' and 'Golden Delicious', have chlorophyll and carotenoids as the predominant skin pigments. Drake et al. (1981) reported that the yellow color of 'Golden Delicious' at harvest was enhanced under reduced plant-water status. As color development of both red and yellow apple cultivars is dependent on light reaching the fruit (Lancaster 1992), a reduction in vegetative growth under DI may allow better light penetration into the canopy. Peach skin color varies from an absence of red blush to almost a complete red blush with yellow background color (Sistrunk 1985). The background color is due to carotenoids, and the red pigmentation is due to anthocyanins. Increased light penetration into the canopy enhances fruit-color development in peach (Westwood and Gerber 1958). In grape berries, DI results in greater concentration of anthocyanins which improves wine quality especially color (Freeman 1983; Matthews and Anderson 1988). Pear color is due to chlorophyll and carotenoid pigments, with the development of yellow color depending on chlorophyll breakdown and carotenoid development (Hansen 1955) with blush development due to anthocyanins. A breakdown in chlorophyll required for the development of yellow or red color is inhibited under high nitrogen conditions (Magness et al. 1940). Deficit irrigation reduces the level ofN in apple fruit (Mills et al. 1994; 1996a) and in pear (Raese et al. 1982). Thus, a reduction in fruit N concentration may play an important role in the development of desirable


121

color attributes in deficit-irrigated fruit, but direct experimental data are not available to substantiate this. An important aspect of fruit quality is the occurrence of disorders present at harvest and developed during storage. Apple fruit grown under water deficit have a lower incidence of bitter pit (Guelfat'Reich et al. 1974; Lotter et al. 1985; Irving and Drost 1987), scald (Guelfat'Reich et al. 1974; Lotter et al. 1985), and water core (Lotter et al. 1985). But Goode et al. (1975) observed increased cracking and russeting. Irving and Drost (1987) reported a greater incidence of apple fruit cracking under earlyseason DI. Gpara et al. (1996), reviewing fruit skin splitting and cracking, indicated that fluctuations in soil moisture and especially a sudden increase late in the season, particularly after a dry period, could split the skin of various fruit. Lotter et al. (1985) found an increase in sunburned apple fruit from DI treatments. Deficit-irrigated peach showed less incidence of fungal rot than those on well-watered trees (Li et al. 1989). Raese et al. (1982) reported a reduction in the incidence of alfalfa greening and cork spot in pear fruit grown under DI, as did Brun et al. (1985). The mineral composition of fruit has been linked to the development of physiological disorders, with a certain nutrient concentration required for good storability (Faust 1989). Low Ca levels in apple fruit may result in the development of bitter pit and water core (Faust 1989). Cork spot, a disorder of both apple (Miller 1980) and pear (Raese et al. 1982), is also a Ca-related disorder (Faust 1989). Nitrogen plays an important role in the quality of stored fruit and an increase in the N concentration of apple fruit may increase the incidence of rot (Ericsson 1993). Water deficit reduces N (Goode and Ingram 1971; Ericsson 1993; Mills et al. 1994, 1996a) and Ca (Goode and Ingram 1971; Mills et al. 1994) concentrations in apple fruit. Deficit irrigation may therefore have a negative effect on the applefruit quality by lowering concentrations of Ca, although lowering of N could be considered to have a positive effect. Pear fruit N concentration is also reduced under DI, although Ca concentrations appear to increase (Brun et al. 1985; Raese 1985). Conflicting information on the influence of DI on fruit Ca concentration is probably due to differences in the timing of water deficit and on the mode of transport ofCa in the tree. Calcium is transported in the transpiration stream (Mengel and Kirkby 1987) and, therefore, a reduction in plant transpiration will result in a reduction of Ca transport within the plant. However, with reduced plant-water status, the vegetative growth is suppressed and, therefore, fruit may be preferentially supplied with Ca under dry conditions (Raese 1985). As most Ca is transported and accumulated by apple fruit during the early part of the season, water deficit at this time is more likely to influence fruit Ca concentration (Ferguson and Watkins 1989). Early-season DI fruit are expected

122


to be susceptible to splitting and cracking because these disorders are related to Ca concentration of the fruit (Faust 1989). However, this could be cultivar-dependent because research in this laboratory has not shown any incidence of splitting and cracking in 'Braeburn' apple under various DI regimes irrespective of fruit calcium concentration (Mills et al. 1994; 1996a; 1996b). Mineral concentrations in fruit, such as N, P, K, and Ca, are likely to be affected by irrigation as nutrients are taken up in the soil solution (Faust 1989). A reduction in soil water may result in an increased concentration of elements in the soil solution to levels where ions may precipitate out and become unavailable to the plant (Mengel and Kirkby 1987). In addition, poor soil aeration or low metabolic activity of root also limit nutrient uptake. A low metabolic rate of roots may develop indirectly from reduced soil moisture, leading to a decrease in the photosynthetic activity of leaves and consequently carbohydrate supply to the root (Kramer and Boyer 1995). Fruit mineral nutrition is a complex area of study, but the limited information indicates that Dr, depending on timing and degree, modifies fruit mineral concentration in a way that may result in fruit with better storage attributes. IV. ESTABLISHMENT OF IRRIGATION SCHEDULES FOR DEFICIT IRRIGATION Irrigation timing and amount become a key issue once DI is adopted as a management tool. Measurement of ET (Elfving 1982), or its calculation based on meteorological data as shown by Jones et al. (1985), could be done for partial replacement of soil water by irrigation, so that a predetermined plant/soil water status could be established. Monitoring of plantand/or soil-water status is necessary in DI to ensure that the intended degree of deficit is achieved. Various parameters have been used as indicators of plant-water status including leaf relative water content (Barrs and Weatherley 1962), canopy temperature (Jackson et al. 1981), crop water stress index (Sepaskhah and Kashefipour 1994), leaf chlorophyll fluorescence (Corlett and Choudhary 1993), xylem water potential and stern water potential using the Scholander pressure bomb (McCutchan and ShackeI1992), root system characteristics (Xiloyannis et al. 1993), changes in stem diameter (Simonneau et al. 1993), and rate of sap ascent (Moreshet et al. 1983). Plant-water status is affected by plant and atmospheric conditions and is not a unique function of soil water status (Hsiao 1990). The most com-


123

monly used parameter is plant water potential. Water transport in the soil-plant-atmosphere continuum can be defined by the relationship: [Eq.1] where T is the rate of water uptake (here approximated as the transpiration rate), lfIsoil and lfIleaf are soil and plant water potentials, and R soil and Rplant are resistances to water flow in soil and in plant. Rearranging (Hsiao 1990) gives: lfIleaf = lfIsoil -

T(R soil +

Rplant)

[Eq.2]

This indicates that the relationship between leaf- and soil-water potentials depends on transpiration rate, which is affected by the evaporative demand (ED) of the atmosphere. A conceptual depiction of such a relationship is shown in Fig. 4.4, adapted from Hsiao (1990), and demonstrates that the degree to which leaf-water potential is lower than the soil-water potential depends on the ED which is affected by radiation, wind speed, atmospheric temperature, and humidity (De Jager and van Zyl 1989). Eq. 2 also shows that the difference between leaf- and soilwater potentials depends on the hydraulic resistance to water flow through the soil-plant system. Jones et al. (1985) reported that fruit trees, such as Prunus and Malus species, have a lower root density than herbs. The soil component of hydraulic resistance will become more significant for these trees than for herbs at a high soil-water potential because transpiration causes the soil adjacent to the roots to become drier than the bulk of the soil. However, Jones et al. (1985) also reported that the great extent of fruit tree roots enables them to reach a greater soil volume and therefore to maintain adequate leaf-water potential and transpiration for a longer time than many shallow-rooting species. A lower leaf-water potential at higher ED will help maintain water transport at a lower soil-water potential. Fig. 4.4 shows that leaf-water potential initially declines in parallel with soil-water potential but will decrease faster as the soil becomes drier. This is because of the nonlinear decrease in the hydraulic conductivity of the drier soil, with the resistance to water flow in the soil rapidly becoming the more limiting factor (Hsiao 1990). This analysis has implications for the choice of a suitable irrigation strategy for deciduous orchards. Eq. 2 shows that irrigation timing cannot be based solely on the measurement of plant-water status. While the soil could be wet in high ED situations, low plant-water status may result from a high transpiration,


124

o ......... Soil ......

4J

......... .........

Leaf

4J

(

-

- - - - - - : l........

......... ......

Equal Potential

.........

(_)

...... .........

.........

)

Fig. 4.4. Conceptual depiction ofthe influence of evaporative demand (ED) ofthe atmosphere and the resultant transpiration rate (T) on the relationship between soil-water potential (Soil lfI) and leaf-water potential (Leaf lfI) over a range of decreasing soil lfI. Dashed line indicates when soil- and plant-water potentials are in equilibrium (adapted from Hsiao 1990).

and irrigation will not help. This is exemplified by the midday wilting observed in some crops even while the soil is quite moist. Thus, a suitable method for irrigation scheduling should consider the prevailing ED which will influence plant-water status when measuring soil-water status. In this case, the parameters ofEq. 2 should be considered in the irrigation scheduling. The water balance method is one of the oldest and simplest methods and uses a knowledge of soil moisture, irrigation application depth, rainfall, ET, runoff, and deep percolation below the root zone to predict

125


the amount of water available in the root zone on a given day. A practical approach for keeping a record of these and using it for irrigation scheduling is described as the checkbook method by Smith (1993). Irrigation timing is thus based on measurement of root-zone water content (Fig. 4.5; SInith 1993), with a consideration of impending ET which has implications for plant-water status according to Eq. 2. With this method, one can implement a controlled DI that places the plant under the desired level of water deficit. Fig. 4.5 shows a simplified version of soil-water changes with time, but in actual practice this change is rarely linear. However, this should not seriously detract from using the figure as an irrigation guide. The requirements are to measure the root-zone moisture and to decide on the timing ofirrigation, based on the approaching ET rates. Root-zone water measurements could be done by using gravimetric methods, tensiometers, neutron probes, and more recently with the very useful technique of time domain reflectometry (TDR). A description of the TDR method is given by Topp and Davis (1985). We have used this TDR method successfully and we have been able to develop a desired stress level in apple trees (Mills et al. 1996b). The approaching ET rates could either be calculated employMeasured soil-water content

Forecast

..... c:

.....c:(1) o()

o

(f)

High Ave ET ET

Low ET

Probable irrigation dates Today

Time (days) Fig. 4.5. Scheduling irrigation based on the measurements of soil-water content and evapotranspiration (ET) (adapted from Smith 1993).

126


ing meteorological data and using a crop factor as described by Allen (1993), or from weather station networks if available. The orchardist's knowledge and experience is an important factor here. V. FUTURE PROSPECTS Global water consumption has tripled in the last 40 years (Postel 1993) and continues to increase as population grows. As irrigation uses more than 85 % of the total water consumption, effective DI management has the potential to conserve water and to limit the environmental impact of irrigation by reducing leaching of nutrients and pesticides into groundwater. Numerous physiological attributes of the fruit tree are also modified under DI, and the periodic timing of water stress has benefits for fruit production. Early-season DI, applied during rapid shoot growth and slow fruit growth, is now an established method of irrigation management. Significant research in this area has shown this over the last 15 years. Late-season DI also has application in some deciduous fruit cultivars but, due to the possibility of reduced fruit yield, it should be used with caution. Postharvest DI has application with early-ripening cultivars which have as many as 120 growing days after harvest. A water deficit throughout the season is not recommended in the deciduous fruit crops discussed in this review. Research on DI has focused more on growth and yield components than on fruit quality. Information on the effect ofDI on important fruit attributes such as firmness, mineral concentration, and acidity is equivocal. More research is needed in these areas especially on changes of fruit mineral composition under DI. Calcium and N play important roles in fruit physiology and quality, and more research is warranted on how they are affected by DI and to determine whether changes in minerals induced by plant-water status relate directly to changes in fruit quality. Studies on DI have mainly focused on early-season DI. Lateseason DI, which might reduce the incidence of fruit disorders in some cultivars and improve some fruit quality attributes, has received little attention. This is also the case with postharvest DI, which might have implications for reducing vegetative growth and therefore pruning cost for species such as peach and cherry that continue to grow after fruit harvest. In DI research, more emphasis has also been placed on the water relations of the plant than on those of the fruit. Information on the latter is very


127

limited and more needs to be known about the changes in the water relations components of the fruit as a plant undergoes water stress. Osmoregulation by the fruit is more a matter of conjecture, and confirmation is required as this process may have practical ramifications. Osmotic adjustment may be the reason for increase of fruit growth after rewatering of deficit-irrigated trees as shown for Asian pear by Behboudian et al. (1994). More research is recommended for this area of water relations. LITERATURE CITED Ackermann, J., M. Fischer, and R Amado. 1992. Changes in sugars, acids, and amino acids during ripening and starage of apples (cv. Glockenapfel). J. Agr. Food Chern. 40: 1131-1134.

Allen, R G. 1993. New approaches to estimate crop evapotranspiration. Acta Hart. 335: 287-294.

Assaf, R, 1. Levin, and B. Bravdo. 1975. Effect of irrigation regimes on trunk and fruit growth rates, quality and yield. J. Hart. Sci. 50:481-493. Barrs, H. D., and P. E. Weatherley. 1962. A re-examination of the relative turgidity technique for estimating water deficits in leaves. Austral. J. BioI. Sci. 15:413-428. Behboudian, M. H., and G. S. Lawes. 1994. Fruit quality in 'Nijisseiki' Asian pear under deficit irrigation: physical attributes, sugar and mineral content, and development of flesh spot decay. New Zealand J. Crop Hart. Sci. 22:393-400. Behboudian, M. H., G. S. Lawes, and K. M. Griffiths. 1994. The influence of water deficit on water relations, photosynthesis and fruit growth in Asian pear (Pyrus seratina Rehd.). Scientia Hart. 60:89-99. Boland, A. M., P. D. Mitchell, P. H. Jerie, and 1. Goodwin. 1993. The effect of regulated deficit irrigation on tree water use and growth of peach. J. Hart. Sci. 68:261-274. Brun, C. A., J. T. Raese, and E. A. Stahly. 1985. Seasonal response of 'Anjou' pear trees to different irrigation regimes. II. Mineral composition of fruit and leaves, fruit disorders and fruit set. J. Am. Soc. Hart. Sci. 110:835-840. Caspari, H. W. 1993. The effect of water deficit on the water balance and water relations of Asian pear trees (Pyrus seratina Rehd., cv. Hosui) growing in lysimeters. Ph.D. Thesis, Bonn Univ., Germany. Caspari, H. W., M. H. Behboudian, and D. J. Chalmers. 1994. Water use, growth, and fruit yield of 'Hosui' Asian pears under deficit irrigation. J. Am. Soc. Hart. Sci. 119:383-388. Caspari, H. W., M. H. Behboudian, D. J. Chalmers, B. E. Clothier, and F. Lenz. 1996. Fruit characteristics of 'Hosui' Asian pears after deficit irrigation. HartScience 31:162. Chalmers, D. J. 1989. A physiological examination of regulated deficit irrigation. New Zealand J. Agr. Sci. 23:44-48. Chalmers, D. J., and B. van den Ende. 1975. Productivity of peach trees: factars affecting dry-weight distribution during tree growth. Ann. Bot. 39:423-432. Chalmers, D. J., P. D. Mitchell, and 1. van Heek. 1981. Control of peach tree growth and productivity by regulated water supply, tree density and summer pruning. J. Am. Soc. Hart. Sci. 106:307-312. Chalmers, D. J., P. D. Mitchell, and P. H. Jerie. 1984. The physiology of growth control of peach and pear trees using reduced irrigation. Acta Hart. 146:143-149.

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Chalmers, D. J., P. D. Mitchell, and P. H. Jerie. 1985. The relation between irrigation, growth and productivity of peach trees. Acta Hort. 173 :283-288. Chalmers, D. J., G. Burge, P. H. Jerie, and P. D. Mitchell. 1986. The mechanism ofregulation of 'Bartlett' pear fruit and vegetative growth by irrigation withholding and regulated deficit irrigation. J. Am. Soc. Hort. Sci. 111:904-907. Corlett, J. K, and R Choudhary. 1993. Chlorophyll fluorescence for water deficit detection in horticultural crops? Acta Hort. 335:241-244. Cripps, J. K 1. 1971. The influence of soil moisture on apple root growth and root: shoot ratio. J. Hort. Sci. 46:121-130. Crisosto, C. H., R S. Johnson, J. G. Luza, and G. M. Crisosto. 1994. Irrigation regimes affect fruit soluble solids concentration and rate of water loss of 'O'Henry' peaches. HortScience 29:1169-1171. De Jager, J. M., and W. H. van Zyl. 1989. Atmospheric evaporative demand and evaporation coefficient concepts. Water SA 15:103-110. Degman, K S., J. R Furr, and J. R Magness. 1932. Relation of soil moisture to fruit bud formation in apples. J. Am. Soc. Hort. Sci. 29:199-201. Drake, S. R, K 1. Proebsting, M. O. Mahan, andJ. B. Thompson. 1981. Influence oftrickle and sprinkle irrigation on 'Golden Delicious' apple quality. J. Am. Soc. Hort. Sci. 106:255-258.

Durand, G. 1990. Effects of RDI on apple tree (cv. Royal Gala) growth, yield and fruit quality in a humid environment. Ph.D. Thesis, Massey Univ., Palmerston North, New Zealand. Ebel, R c., K 1. Proebsting, and, M. K Patterson. 1993. Regulated deficit irrigation may alter apple maturity, quality and storage life. HortScience 28:141-143. Ebel, R c., K L. Proebsting, and R G. Evans. 1995. Deficit irrigation to control vegetative growth in apple and monitoring fruit growth to schedule irrigation. HortScience 30:1229-1232.

Elfving, D. C. 1982. Crop responses to trickle irrigation. Hort. Rev. 4:1-48. Ericsson, N. A 1993. Quality and storability in relation to fertigation of apple trees cv. Summerred. Acta Hort. 326:73-83. Faust, M. 1989. Physiology of temperate zone fruit trees. Wiley, New York. Ferguson, 1. B., and C. B. Watkins. 1989. Bitter pit in apple fruit. Hort. Rev. 11:289-355. Freeman, B. M. 1983. Effects of irrigation and pruning of Shiraz grapevines on subsequent red wine pigments. Am. J. Enol. Vitic. 34:23-26. Girona, J., M. Mata, D. A Goldhamer, R S. Johnson, and T. M. DeJong. 1993. Patterns of soil and tree water status and leaf functioning during regulated deficit irrigation scheduling in peach. J. Am. Soc. Hort. Sci. 118:580-586. Glenn, D. M., and W. V. Welker. 1989. Peach root development and tree hydraulic resistance under tall fescue sod. HortScience 24:117-119. Goldhamer, D. A, G. S. Sibbett, R C. Phene, and D. G. Katayama. 1994.. Early irrigation cutoff has little effect on French prune production. Cal. Agr. 48:13-17. Goode, J. K, and K. J. Hyrycz. 1964. The response of Laxton's superb apple trees to different soil moisture conditions. J. Hort. Sci. 39:254-276. Goode, J. K, and J. Ingram. 1971. The effect ofirrigation on the growth, cropping and nutrition of Cox's Orange Pippin apple trees. J. Hort. Sci. 46:195-208. Goode, J. K, M. M. Fuller, and K. J. Hyrycz. 1975. Skin cracking of Cox's Orange Pippin apples in relation to water stress. J. Hort. Sci. 50:265-269. Goodwin, 1., and P. Jerie. 1989. Deficit irrigation of Chardonnay grapevines during flowering. Acta Hort. 240:275-278. Guelfat'Reich, S., R Assaf, B. A Bravdo, and 1. Levin. 1974. The keeping quality of apples in storage as affected by different irrigation regimes. J. Hort. Sci. 49:217-225.


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Guelfat'Reich, S., and R. Ben-Arie. 1979. Effect of irrigation on fruit quality at harvest and during storage. Proc. XVth Int. Congr. Refrig. 3:423-427. Haller, M. H., and P. 1. Harding. 1937. Relation of soil moisture to firmness and storage quality of apples. Proc. J. Am. Soc. Hort. Sci. 35:205-211. Hansen, E. 1955. Factors affecting post-harvest color development in pears. Proc. Am. Soc. Hort. Sci. 66:118-124. Hargreaves, G. H., and Z. A. Samani. 1984. Economic considerations of deficit irrigation. J. Irr. Drain. Eng. 110:343-358. Hsiao, T. C. 1973. Plant responses to water stress. Annu. Rev. Plant. Physiol. 24:519-570. Hsiao, T. C. 1990. Plant-atmosphere interactions, evapotranspiration, and irrigation scheduling. Acta Hort. 278:55-66. Hsiao, T. C. 1993. Growth and productivity of crops in relation to water stress. Acta Hort. 335:137-148.

Hsiao, T. c., E. Acevedo, E. Fereres, and D. W. Henderson. 1976. Water stress, growth and osmotic adjustment. Phil. Trans. R. Soc. London, Ser. B. 273:471-500. Iancu, M. 1985. Growth rate of apple trunk and fruit-additional indicators for water needs of fruit trees. Acta Hort. 171:417-425. Irving, D. D., and J. H. Drost. 1987. Effects of water deficit on vegetative growth, fruit growth and fruit quality in Cox's Orange Pippin apple. J. Hort. Sci. 62:427-432. Jackson, R. D., S. B. Idso, R. J. Reginato, and P. J. Pinter. 1981. Canopy temperature as a crop water stress indicator. Water Resource Res. 17:1133-1138. Jerie, P. H., P. D. Mitchell, and I. Goodwin. 1989. Growth of Williams' Bon Chretien pear fruit under regulated deficit irrigation (RDI). Acta Hort. 240:271-274. Johnson, R. S., D. F. Handley, and T. M. DeJong. 1992. Long-term response of early maturing peach trees to postharvest water deficits. J. Am. Soc. Hort. Sci. 117:881-886. Jones, H. G., A. N. Lakso, and J. P. Syvertsen. 1985. Physiological control of water status in temperate and subtropical fruit trees. Hort. Rev. 7:301-344. Kappel, F., R. Fisher-Fleming, and E. J. Hogue. 1995. Ideal pear sensory attributes and fruit characteristics. HortScience 30:988-993. Kilili, A. W., M. H. Behboudian, and T. M. Mills. 1996. Composition and quality of 'Braeburn' apples under reduced irrigation. Scientia Hort 67:1-11. Kingston, C. M. 1991. Maturity indices for apple and pear. Hort. Rev. 13:407-432. Kramer, P. J. 1988. Changing concepts regarding plant water relations. Plant Cell Environ. 11 :565-568.

Kramer, P. J., and J. S. Boyer. 1995. Water relations of plants and soils. Academic Press, New York. Lakso, A. N. 1983. Morphological and physiological adaptations for maintaining photosynthesis under water stress in apple trees. p. 85-93. In: R. Marcelle, H. Clijsters, and M. van Poucke(eds.), Effects of stress on photosynthesis. Martinus NijhoffiDr. W. Junk, The Hague, The Netherlands. Lakso, A. N. 1985. The effects of water stress on physiological processes in fruit crops. Acta Hort. 171:275-290. Lampinen, B. D., K. A. Shackel, S. M. Southwick, B. Olson, J. T. Yeager, and D. Goldhamer. 1995. Sensitivity of yield and fruit quality of French prune to water deprivation at different fruit growth stages. J. Am. Soc. Hort. Sci. 120:139-147. Lancaster, J. E. 1992. Regulation of skin color in apples. Crit. Rev. Plant Sci. 10:487-502. Landsberg, J. J., and H. G. Jones. 1981. Apple orchards. p. 419-469. In: T. T. Kozlowski (ed.), Water deficits and plant growth, vol. VI. Academic Press, London. Layne, R. E. c., C. S. Tan, and J. M. Fulton. 1981. Effect of irrigation and tree density on peach production. J. Am. Soc. Hort. Sci. 106:151-156.

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Li, S. H., J. G. Huguet, P. G. Schoch, and P. Orlando. 1989. Responses of peach tree growth

and cropping to soil water deficit at various phenological stages of fruit development. J. Hart. Sci. 64:541-552. Li, S. H., and J. G. Huguet. 1990. Controlling water status of plants and scheduling irrigation by the micromorphometric method for fruit trees. Acta Hart. 278:333-342. Lotter, J. de V., D. J. Beukes, and H. W. Weber. 1985. Growth and quality of apples as affected by different irrigation treatments. J. Hart. Sci. 60:181-192. Magness, J. R., 1. P. Batjer, and 1. O. Regeimbal. 1940. Correlation of fruit color in apples to nitrogen content in leaves. Proc. Am. Soc. Hart. Sci. 37:39-42. Mandre, 0., M. Rieger, S. C. Myers, R. Seversen, andJ. 1. Regnard. 1995. Interaction ofroot confinement and fruiting in peach. J. Am. Soc. Hart. Sci. 120:228-234. Matthews, M. A., and M. M. Anderson. 1988. Fruit ripening in Vitis vinifera 1.: responses to seasonal water deficits. Am. J. Enol. Vitic. 39:313-320. McCutchan, H., and K. A. Shackel. 1992. Stem-water potential as a sensitive indicator of water stress in prune trees (Prunus domestica 1. cv. French). J. Am. Soc. Hart. Sci. 117:607-611. Mengel, K., and E. A. Kirkby. 1987. Principles of plant nutrition, 4th ed. Int. Potash Institute, Warblaufen-Bern, Switzerland. Miller, R. H. 1980. The ontogeny and cytogenesis of cork spot in 'York Imperial' apple fruit. J. Am. Soc. Hart. Sci. 105:355-364. Mills, T. M., M. H. Behboudian, and B. E. Clothier. 1996a. Preharvest and storage quality of 'Braeburn' apple fruit grown under water deficit conditions. New Zealand J. Crop Hart. Sci. 24:159-166. Mills, T. M., M. H. Behboudian, and B. E. Clothier. 1996b. Water relations, growth, and composition of 'Braeburn' apple fruit under deficit irrigation. J. Am. Soc. Hart. Sci. 121:286-291. Mills, T. M., M. H. Behboudian, P. Y. Tan, and B. E. Clothier. 1994. Plant water status and fruit quality in 'Braeburn' apples. HartScience 29:1274-1278. Mitchell, P. n, and D. J. Chalmers. 1982. The effect of reduced water supply on peach tree growth and yields. J. Am. Soc. Hart. Sci. 107:853-856. Mitchell, P. D., and D. J. Chalmers. 1983. A comparison of microjet and point emitter (trickle) irrigation in the establishment of a high-density peach archard. HortScience 18:472-474. Mitchell, P. D., D. J. Chalmers, P. H. Jerie, and G. Burge. 1986. The use of initial withholding of irrigation and tree spacing to enhance the effect of regulated deficit irrigation on pear trees. J. Am. Soc. Hart. Sci. 111 :858-861. Mitchell, P. D., P. H. Jerie, and D. J. Chalmers. 1984. The effects of regulated water deficit on pear tree growth, flowering, fruit growth and yield. J. Am. Soc. Hart. Sci. 109:604-606. Mitchell, P. D., B. van den Ende, P. H. Jerie, and D. J. Chalmers. 1989. Responses of 'Bartlett' pear to withholding irrigation, regulated deficit irrigation and tree spacing. J. Am. Soc. Hart. Sci. 114:15-19. Mareshet, S., Y. Cohen, and M. Fuchs. 1983. Response of mature 'Shamouti' orange trees to irrigation of different soil volumes at similar levels of available water. Irr. Sci. 3:223-236. Opara,1. U., C. J. Studman, and N. H. Banks. 1996. Fruit skin splitting and cracking. Hort. Rev. 19:217-262. Postel, S. 1993. Running dry. The Unesco courier, (May edition):19-22. Powell, D. B. B. 1974. Some effects of water stress in late spring on apple trees. J. Hart. Sci. 49:257-272.


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Proebsting, E. 1., J. E. Middleton, and S. Roberts. 1977. Altering fruiting and growth characteristics of 'Delicious' apple associated with irrigation method. HortScience 12:349-350. Proebsting, E. 1., P. H. Jerie, and J. Irvine. 1989. Water deficits and rooting volume modify peach tree growth and water relations. J. Am. Soc. Hort. Sci. 114:368-372. Raese, J. T., C. A. Brun, and E. J. Seeley. 1982. Effect of irrigation regimes and supplemental nitrogen on alfalfa greening, cork spot and fruit quality of 'd'Anjou' pears. HortScience 17:666-668. Raese, J. T. 1985. Nutrition practices to improve quality in d'Anjou pears discussed. Goodfruit Grower 36:42-44. Richards, D. 1985. Tree growth and productivity-the role of roots. Acta Hort. 175:27-36. Richards, D., and R N. Rowe. 1977. Root-shoot interactions in peach: the function of the root. Ann. Bot. 41:1211-1216. Sepaskhah, A. R, and S. M. Kashefipour. 1994. Relationships between leaf water potential, CWSI, yield and fruit quality of sweet lime under drip irrigation. Agr. Water Mgmt. 25:13-21. Simonneau, T., R Habib, and A. Lecombe. 1993. Diurnal changes in stem diameter and plant water content in peach trees. Acta Hort. 335:191-196. Sistrunk, W. A. 1985. Peach quality assessment: fresh and processed. p. 1-46. In: H. E. Pattee (ed.), Evaluation of quality of fruits and vegetables. AVI, Westport, CT. Smith, S. W. 1993. Schedule irrigation with the checkbook method. Grounds Maint. 28:21-26. Syvertsen, J. P. 1985. Integration of water stress in fruit trees. HortScience 20:1039-1043. Taerum, R 1964. Effects of moisture stress and climatic conditions on stomatal behaviour and growth in Rome beauty apple trees. Proc. Am. Soc. Hort. Sci. 85:20-32. Tanji, K. K. 1993. Ground water contamination concerns in horticultural production systems. Acta Hort. 335:37-44. Topp, G. c., and J. 1. Davis. 1985. Measurement of soil water content using time-domain reflectometry: a field evaluation. Soil Sci. Soc. Am. J. 49:19-24. Turner, N. C. 1986. Adaptation to water deficit: a changing perspective. Austral. J. Plant. Physiol. 13:175-190. van Schilfgaarde, J. 1994. Irrigation-a blessing or a curse? Agr. Water Mgmt. 25:203-219. Westwood, M. N. 1988. Temperate zone pomology, 2nd ed. Timber Press, Portland, OR Westwood, M. N., and R K. Gerber. 1958. Seasonal light intensity and fruit quality factors as related to the method of pruning fruit trees. Proc. Am. Soc. Hort. Sci. 72 :85-91. Westwood, M. N., and A. N. Roberts. 1970. The relationship between cross-sectional area and weight of apple trees. J. Am. Soc. Hort. Sci. 95:28-30. Xiloyannis, c., R Massai, D. Piccotino, G. Baroni, and M. Bovo. 1993. Method and technique of irrigation in relation to root system characteristics in fruit growing. Acta Hort. 335:505-510.

5

Germplasm Resources of Pineapple Ceo Coppens d'Eeckenbrugge CIRAD-FLHOR/IPGRI c/o CIAT AA 6713 Cali, Colombia Freddy Leal DCV Facultad de Agronomia Apartado 4736 Maracay, Aragua, Venezuela Marie-France Duval CIRAD-FLHOR B.P.153 Fort-de-France, Martinique, FWI

1. Introduction A. Historical Review

B. Pineapple Breeding II. Genetic Base and Genetic Diversity A. Taxonomy of Bromeliaceae and Ananas B. Pineapple Cultivars C. Mutations in Pineapple III. Problems of Genetic Significance A. Fertility and Incompatibility B. Environmental Adaptation C. Propagation Adaptability D. Productivity E. Pest and Disease Resistance 1. Insects 2. Nematodes 3. Diseases


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G. COPPENS, F. LEAL, AND M.-F. DUVAL

F. Fruit Quality 1. Fresh Market 2. Processing IV. Germplasm Maintenance and Utilization A. Main Existing Collections B. Field Collection Management 1. Introductions 2. Evaluation C. In Vitro Germplasm Conservation D. Seed Conservation E. Problems in Evaluation and Conservation 1. Adapted Cultural Practices 2. Loss of Genotypes 3. Somaclonal Variation V. Future Prospects Literature Cited

I. INTRODUCTION

A. Historical Review On November 4, 1493, Christopher Columbus reached Guadeloupe in the Lesser Antilles and, according to the chronicles of Pedro Martyr de Angleria (1530), found the plant and fruit of the pineapple [Ananas comosus (L.) Merr.], syn A. sativus Schultes f., in a small indian village in the southern part of the island. This first contact of the European with the fruit was confirmed by Michael de Cuneo in 1494: "There were some (plants) like artichoke plants, but four times as tall, which gave a fruit in the shape of a pine cone, twice as big, which is excellent, and it can be cut with a knife like a turnip, and it seems to be wholesome" (Morrison 1973). Columbus also observed the pineapple in Puerto Bello (1502) and in the Isthmus of Panama (1503). According to Gonzalo Fernandez de Oviedo (1535), the pineapple was very common in the Caribbean basin and also on the South America mainland, where it was known under different names. This author also made an excellent description of the plant and its fruit, recording ways to cultivate it, and presented the earliest pineapple drawing. However, de Las Casas (1550), commenting about the pineapple cultivation in La Hispaniola, claimed that "originally they were not found in the island, rather they were brought from San Juan." The earliest report of the pineapple in Central and South America is by Pigafetta (1519), in the Rio de Janeiro area: "This fruit resembles a pine cone and is extremely sweet and savory; in fact, it is the most exquisite fruit in existence." This report was followed by many others in areas corresponding to Mexico (Ciudad Real

5. GERMPLASM RESOURCES OF PINEAPPLE

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1584); Nicaragua and Costa Rica (Lopez de Velazco 1754), Colombia (Cieza de Leon 1553); Venezuela, Brazil, and Paraguay (Muratori 1743); and Ecuador (Collins 1951; Leal 1989). Pineapple was also observed far inland by Gaspar de Carvajal, who navigated in 1542 with Francisco de

Orellana along the Amazon River and declared: "The land is very large and beautiful, and very abundant of meals and fruits, like pineapple and pears (avocados)." Surprisingly, the pineapple plant was not reported West of the Andes. According to the chronicles, it was not grown on the Peruvian coastal lowlands (virreinato of Peru), but the fruit was imported from "the Andes" (Leal 1989). This wide distribution and cultivation indicates without doubt that native Americans had domesticated and dispersed the plant well before the arrival of Columbus. They had a thorough knowledge of the plant, differentiating cultivars and wild types. Fernandez de Oviedo (1535) described three cultivars from La Hispaniola: 'Yayama', 'Yayagua', and 'Boniama'. In his Relaci6n del Descubrimiento del Rio Apure (an Orinoco effluent), Jacinto de Carvajal (1647) described "small wild pineapples, white and very green, with lots of black stones or seeds." Similar observations were reported by Father Gumilla (1741). The words nana and anana are used commonly throughout the Amazon and Orinoco basins, as well as in southern South America. "The word 'anana' from the carib 'nana' is also present in the galibi and chaima dialects, as well as in the arawak and tupi. In the latter the form 'anana' already exists. In tupi nana is the plant and anana is the fruit" (Alvarado 1939). The Spanish pina and the English pineapple came from the comparison with the exotic pinecone. The Brazilian name abacaxi, originally designating particular cultivars, is derived from the guarani word for the maize ear (Bertoni 1919). In addition to the fresh fruit, pineapple had such varied uses as wine making (Raleigh 1596), fiber production, emmenagogue, abortifacient, antiamoebic, vermifuge, correction of stomach disorders, and poisoning of arrow points (Leal and Coppens d'Eeckenbrugge 1996). As early as 1557, Andre Thevet mentioned the nana as "an efficacious remedy against many diseases.... Even if the fruit is not ripe, its juice is astringent, attacking the gums and provoking mouth ulceration." Modern studies have confirmed the emmenagogue and abortifacient effects of green pineapple (Nakayama et al. 1993). Similarly, neighbor species were domesticated or gathered, as Ananas bracteatus (Lindley) Schultes f., used for its fruit and fiber, and as an abortifacient and emmenagogue by the Tupi-Guarani people in Paraguay (Bertoni 1919), or A.lucidus Miller and Pseudananas sagenarius (Arruda da Camara) Camargo, used for their strong and long fibers. Some bromeli-

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ads yield edible fruits which are locally consumed for their similar gustative and pharmaceutical properties [e.g., Bromelia pinguin 1., B. chrysantha Jacquin., and B. nidus-puellae (Andre) Andre ex. Mez., known as piiiuelas] but only pineapple gives a fruit of economic importance. Other genera are cultivated as ornamentals or gathered as sources of fibers. Some wild bromeliads are consumed by the natives for their vegetative parts (hearts, young stems, and leaves) (Patino 1963, Benzing 1980). The Europeans were particularly fascinated by the pineapple. Since their first travels, the Spaniards imported pineapple fruits, which were eaten in Spain when the trip was short. The fruit was presented to the emperor Charles V who found it very pretty but refused to taste it (Humboldt 1808). The pineapple not only traveled to Europe but was also carried in the great voyages of the 16th and 17th centuries. Unlike the fruit, the plant and its vegetative propagules are tough, durable, and very resistant to drought, which greatly facilitated its diffusion around the world. In 1505, the Portuguese introduced the pineapple to the island of St. Helena, before 1549 to Madagascar, and in 1548 to southern India. It was also reported in the Philippines in 1558, coming from China, and naturalized in Java in 1599. Its cultivation was reported in Nepal in 1601, in Guinea in 1602 (cultivated by the natives), in Singapore in 1637, and in Formosa in 1650 (Laufer 1929, cited by Collins 1960; Chadha and Pareek 1988). Pineapple was readily accepted as an outstanding new fruit and other uses also were recognized throughout the world. In 1571, the natives of the Philippines were already making the now traditional "pina cloth" from pineapple leaf fibers (Collins 1960), and the natives of Malaysia used it to regulate human reproduction (Gimlette 1915, cited by de Laszlo and Henshaw 1954). The pineapple was cultivated in greenhouses in Europe, becoming a fashionable (and expensive) plant for kings, botanists, and horticulturists. According to Loudon (1822), the plant was introduced to England in 1690 by Bentick, later Count of Portsmouth; but the first attempts at cultivation of pineapple in Europe date to the end of the 16th century, when Le Cour (or La Court), a very rich Flemish trader, grew it in Drieoeck, close to Leyden. The introduction of pineapple cultivars was very active until the late 19th century. Griffin (1806) stated that it would be an endless and unnecessary work to enumerate all the pineapple cultivars because many of them are worthless and their cultivation cumbersome, and he described the 10 most interesting cultivars, mentioning as the best one the 'Oval pine-apple' or 'Queen-pine'. This cultivar, brought from Barbados, was famous in England before 1661 (Evelyn 1661, cited by Collins 1960). Loudon (1822) described 16 good cultivars and 7 inferior ones, adding that new types were frequently imported


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from the Antilles. In his classification, Munro (1835) considered four species in the genus, with 48 cultivars for A. sativa. These cultivars were classified in classes and divisions on the basis of spininess, fruit shape, and flower color. Beer (1857) stated that A. sativus comprises 68 cultivars and that their list was still increasing regularly. Because of the short life of the fruit, the economic importance of pineapple developed along with efficient transportation and preservation. Commercial transportation of pineapple started in the 19th century. Loudon (1822) stated that "of late years the Pine Apple has been sent to England in abundance, attached to the entire plant, and a cargo has arrived from Providence Island, in the Bermudas, in six weeks. This facility of cultivation, and their more general culture, has greatly lessened their price and rendered them common." These importations obviously contributed to the introduction of new cultivars. In any event, the massive commercialization of fresh pineapple had to wait for better means of transportation: modern refrigerated ships and planes. Preservation techniques were similarly improved, from the first jams exported by the European colonists of Brazil and New Spain (Mexico) (Thevet 1557, Acosta 1590) to canned pineapple at the end of the 19th century. Finally, canned pineapple development was boosted by the invention of the Henry Ginaca machine in Hawaii, at such extent that the international exchanges are now largely superior for the canned products than for the fresh fruit. The processing industry has made the pineapple well known throughout the world and has encouraged the shipment of the rather perishable ripe whole fruit. The tendency is to move production areas closer to the fresh fruit markets, so there is particularly high potential in the tropical areas close to the United States and the large European markets. Many of these areas, however, lack the technology for high productivity. Pineapple is now the third most important tropical fruit, cultivated in all tropical and subtropical countries. Production exceeded 12 million t in 1995, which represents a 20% increase from the early 1980s. Most of this production (70%) is locally consumed as a fresh fruit. World trade mainly consists of processed products, of which 80% of canned slices (1,065,000 t) and juice concentrate (215,000 t) is supplied by Thailand and the Philippines. The fresh fruit market (680,000 t) is dominated by the Philippines, Costa Rica, and Cote d'Ivoire, which supplies 60% ofthe European market, the leading importer with more than 226,000 t (FAG 1994; Loeillet 1996b). Thailand is the leading pineapple producer (22.7% of world production), but there are large commercial plantings in the Philippines (10.1 0/0), China (7.3%), Brazil (8.4%), India (6.9%), United States (Hawaii and Puerto Rico) (3.1 %), Mexico (2.4%), Kenya (2.3%),

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and Cote d'Ivoire (1.7%) (FAO, 1995). About 70% of the world production and 96% of the pineapple used by the processing industries comes from one cultivar, 'Smooth Cayenne'. B. Pineapple Breeding The first pineapple breeding programs occurred in Florida (Webber 1905) in an attempt to produce cultivars adapted to local conditions, but none of the new genotypes survived. Similar pioneer works were conducted in Hawaii by Higgins (cited by Johnson 1935) and V. Holt and coworkers (Williams and Fleisch 1993). The largest pineapple breeding program in Hawaii was conducted from 1914 to 1972 by the Pineapple Growers Association of Hawaii (PGAH) at its experiment station, the Pineapple Research Institute (PRI), under the leadership of K. R. Kerns and J. 1. Collins. The initial objective was to widen the genetic base because of the risk of using a single cultivar, but it was expanded very soon to the development of a cultivar surpassing'Smooth Cayenne'. This work was very comprehensive and included studies on floral biology (cytology, cytogenetics, self-incompatibility), development of procedures to test disease and pest resistance (such as Phytophthora, nematodes, mealybug wilt, bacteria), inheritance of selected traits, and germplasm prospections and evaluation. Their results still constitute obligate references in the present knowledge of pineapple genetics (Collins 1930, 1933a,b, 1934, 1936, 1948, 1949, 1951, 1960; Collins and Carter 1954; Collins and Hagan 1932; Collins and Kerns 1931, 1933, 1938, 1946; Kerns 1931, 1932; Kerns and Collins 1947). The most commonly grown pineapple, 'Smooth Cayenne', was hybridized with more than 17 cultivars. Hybrids were made using' Smooth Cayenne' , 'Monte Lirio', and 'Rondon' with species available at that time, A. ananassoides (Baker) 1. B. Smith, A. bracteatus, A. erectifolius (A. lucidus), and Pseudananas sagenarius. Many hybrids were promising but all were discarded because of some major defects, generally related to pests and diseases or to consumer acceptance. The breeding program was closed in the early 1970s and its hybrids were released to the member companies. The PRI collection was turned over to the USDA germplasm repository in 1968 (Williams and Fleisch 1993). In 1926, Formosa (now Taiwan) started a pineapple breeding program at the Kagi Agricultural Experiment Station where' Smooth Cayenne' was crossed with local cultivars ('Ohi', 'Uhi', 'Anpi', and 'Seihi'). Thirteen out of 2,000 hybrids were selected but their final outcome is unknown. Later crosses between 'Smooth Cayenne' and 'Queen' resulted in cultivars Tainung 1 to 8 (Sakimura and Stanley 1931; Fitchet 1989).


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The first program in the Philippines was conducted from 1921 to 1941. A total of 668 selections were produced by crossing 'Espanola Roja', 'Smooth Cayenne', and 'Buitenzorg' ('Queen'). No hybrid was ever released and all the work was lost. Some work has also been carried out from PRI breeding stock by the Philippine Packing Corporation at Mindanao, but nothing was published (Mendiola et al. 1951). More recently, hybridization at the Institute of Plant Breeding (Los Banos) has been based on crosses between 'Singapore Spanish', 'Smooth Cayenne', and 'Queen'. The objective is a spineless cultivar similar to 'Queen'. The program also considers the creation of dual-purpose cultivars for fruit and fiber using Ananas lucidus germplasm. A promising hybrid was micropropagated (Villegas et al. 1996 and pers. comm.). In the early 1970s, the breeding program of the Malayan Pineapple Industry Board (MPIB) was concentrated on hybridization between 'Sarawak' ('Smooth Cayenne') and 'Singapore Spanish'. In 1974, it was taken over by the Malaysian Agricultural Research Division Institute (MARDI), which released 'MARDI Hybrid 1', a canning cultivar named 'Nanas Johor' (,Johor') but no longer in use because of susceptibility to marbling disease and cork spot. Later crosses involving a local 'Singapore Spanish' strain and a hybrid relative produced 800 seedlings, with a very wide variability and transgressive segregation for 10 out of the 13 traits evaluated. Chan (1991, 1993) stressed the difficulty of finding recombinants with the desirable characteristics within a single genotype. Similar cases of transgressive segregations were observed in a complete diallel between 'Moris' ('Queen'), 'Masmerah' ('Singapore Spanish'), 'Sarawak' ('Cayenne') and 'Johor', when 50,000 hybrids were produced. From these, 303 promising clones were selected mainly on fruit size, square-shouldered fruit shape, flesh color, core diameter, absence of spines, and total soluble solids (TSS). After further evaluation for resistance to diseases and acidity, these selections were trimmed to 13, 6 of which were submitted to field and canning trials. Strong genotype by environmental interactions were observed for most traits. Three hybrids confirmed their good potential either for canning (high and stable yields) or for the fresh fruit (Chan 1989,1991,1993,1996). The pineapple industry in Brazil is mainly based on the cultivars 'Perola' and 'Smooth Cayenne,' which are both susceptible to fusariosis, caused by Fusarium subglutinans (Wollenweb. & Reinking) P. E. Nelson, T. A. Toussoun & Marasas. (basionym F. manilifarme var. subglutinans) (Rohrbach and Schmitt 1994c), a very devastating disease in this country, where it causes as high as 80% losses of marketable fruits (de Matos 1995). Evaluations under artificial inoculation enabled the identification of 25 resistant pineapple accessions, including 20 A. camasus cultivars,

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three clones of A. bracteatus, and two clones of Ananas parguazensis Camargo & Smith. Resistance was also found in other Bromeliaceae, including Pseudananas sagenarius (Cabral et al. 1996). The potential of genetic resistance was so promising that in 1978 the Centro Nacional para Mandioca e Fruticultura of the Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA/CNPMF) started a breeding program to transfer fusariosis resistance to 'Perola' and 'Smooth Cayenne'. Other initial objectives of the program were the improvement of processing qualities, the incorporation of disease and nematode resistance, and adaptation to adverse climatic conditions, especially tolerance to high temperatures during fruit maturity and drought (Giacometti 1978). The resistant cultivars Perolera, Primavera, and Sao Bento, and the tolerant cultivars Roxo de Tefe and Guiana were crossed mainly with 'Smooth Cayenne' and 'Perola', producing over 23,000 resistant hybrids. From 12,000 smooth seedlings, 23 were selected on desirable characteristics such as cylindrical fruit shape, adequate Brix and acidity, short peduncle, and a fruit weight of more than 1.2 kg. These selections must still be submitted to agronomical trials before release. Even though fusariosis has not been reported in most of the pineapple-growing areas of the world, this effort is important because the most commonly planted cultivars, Smooth Cayenne, Queen, Singapore Spanish, and Espanola Roja are susceptible. In 1978, the fruit department of the French Centre de Cooperation Internationale en Recherche Agronomique pour Ie Developpement (CIRAD-FLHOR) started a pineapple breeding program to create cultivars for Cote d'Ivoire exportations of both fresh and processed fruits. In addition to fruit yield and quality and smoothness ofthe plant, the objectives included control of internal fruit breakdown (by increasing ascorbic acid content), better synchrony between external and internal maturation (to avoid green ripe fruits), adaptation to warm and dry climates, and resistance to pests and diseases (mainly nematodes and Phytophthora). About 40,000 hybrids between the cultivars Smooth Cayenne and Perolera were assessed by a multitrait phenotypic index (Cabot 1989). In the late 1980s, the program was progressively split between the fruit department of the Ivorian Institut des ForMs (IDEFOR) and the CIRADFLHOR experimental station in Martinique, where a general objective of diversification and specialization is now emphasized, selecting either for the fresh fruit market (new shapes and colors) or for processing. A first promising hybrid showed superior yield (10% more than 'Smooth Cayenne') and ascorbic acid, and a slightly lower but more stable sugar content. Its drawbacks are peduncle length, basal slips, fibrous pulp, and


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susceptibility to the black spot disease (F. Marie and G. Coppens d'Eeckenbrugge, unpublished). Another promising hybrid produces a globulous to cylindrical, bright red fruit, with large flat eyes and an attractive yellow flesh of good quality. The completely smooth plant is compact with early ratooning, but is susceptible to wilt and black spot. Hno major drawback appears from more extensive trials, it could get a place on the fresh fruit market because of its new and attractive shape and color. Presently, the CIRAD-FLHOR program also considers the development of ornamental pineapples from hybridization between small-fruited genotypes. In Australia, experimental crosses (about 2,000 seedlings produced) were carried out between 'Smooth Cayenne', Hawaiian hybrids, and 'Queen' to incorporate Phytophthora resistance from the Hawaiian hybrids and to improve yield and quality characteristics from the 'Queen' local selections. Several hybrids showed fruit similarity with their 'Queen' parent and improved fresh market characteristics, but on smoothleaved plants (Winks et al. 1985). The hybridization program which produced the 'PRl-57' in Puerto Rico was based on natural crosses between 'Smooth Cayenne' and 'Espanola Roja' (Ramirez et al. 1972). Recently, another hybridization program between these cultivars was started in Cuba (Benega et al. 1993). Hybridization has also been reported in Okinawa (Japan) with more than 40,000 seedlings produced from crosses between the main commercial cultivars. A. ananassoides and A. lucidus were also involved (Kinjo 1993). Most hybridization programs have been based on the few leading cultivars, combining' Smooth Cayenne' with 'Queen', Espanola Roja', 'Singapore Spanish', 'Perola', and 'Perolera' and neglecting the large genetic pool available. Up to now, the results have been poor. From millions of seedlings produced since 1905, there have been created only hybrids of limited quality and local importance, such as 'PRl-57', a poor-quality fruit coming from an open cross, and the 'Tainung' hybrids used in Taiwan. Smaller pineapple improvement programs concentrated on clonal selection, mostly within 'Smooth Cayenne', in Australia (Grozman, 1945; Queensland Dept. of Primary Ind. 1970, Glennie et al. 1985), Brazil, Cuba, Guinea and Cote d'Ivoire, India, Japan, Malaysia (Wee 1979), Mexico (Torres Navarro et al. 1989), Puerto Rico (Mariota 1955), South Africa (Dalldorf 1975a), Taiwan (Fitchet 1989), and Venezuela (Leal et al. 1979; Leal and Garcia 1989). Most ofthese selections were made for agronomic traits to supply the local demand. These works have not produced precise published information. Private companies very probably also have clonal selection programs but the information is unavailable.

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n.


GENETIC BASE AND GENETIC DIVERSITY

A. Taxonomy of Bromeliaceae and Ananas Pineapple belongs to the order Bromeliales, family Bromeliaceae, subfamily Bromelioideae. With about 50 genera and more than 2,000 species, this is the largest family whose natural distribution is restricted to the New World, with the exception of Pitcairnia feliciana (Aug.Chev.) Harms & Mildbr., which is native to Guinea. It is distributed in a wide range of habitats, from the hot and humid tropics to the cold and dry subtropics, covering a wide area from the center of the United States to the northern regions of Argentina and Chile (Smith 1934). The Bromeliaceae are usually characterized by a short stern, a rosette of narrow, stiffleaves, terminal inflorescences in the form of racemes or panicles, hermaphroditic and actinomorphic trimerous flowers with well-differentiated calyx and corolla, six stamens, and superior trilocular ovary. Fruits are capsules or berries and contain small naked, winged, or plumose seeds with a reduced endosperm and a small embryo. Most species are epiphytic or saxicolous, but some are terrestrial. They are particularly adapted to water economy based on (1) rosette structure, (2) ability to absorb water and nutrients through their waxy leaves and aerial roots, (3) ability to store water in specialized aquiferous leaf tissue, (4) multicellular trichomes limiting evapotranspiration, and (5) CAM metabolism. Their root system is not well developed and functions mostly to anchor the plant. The Bromeliaceae are divided into three subfamilies: the Pitcarnioideae, the Tillandsioideae, and the Bromelioideae. The Pitcarnioideae are almost terrestrial, with armed leaf margins, hypogenous or epygenous flowers, and dry dehiscent capsules containing naked or appendaged seeds. The Tillandsioideae are mostly epiphytic, with smooth leaf margins, flowers usually hypogenous, and dry dehiscent capsules containing many plumose seeds. The Bromelioideae are epiphytic, frequently spiny, with usually epygenous flowers, and berries containing naked seeds. They show a tendency to fusion of parts, fusion of their carpels to make an indehiscent fruit, formation of an inferior ovary, and fusion of sepals, petals, and filaments. As stated by Smith (1934), "Ananas capped the fusion tendency by merging the whole inflorescence, flowers, bracts and all into one massy compound fruit." Indeed, Ananas and Pseudananas are the only genera in the family whose flowers are fused and develop into a sorosetype fruit. Pseudananas is monotypic with P. sagenarius [from sagena (net) referring to its native use for fiber] from southern Brazil, southeastern Paraguay, and northeastern Argentina.


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Contrary to Ananas, the tetraploid Pseudananas sagenarius (2n 100) is characterized by a complete lack of crown and asexual repro-

duction by stolons. Its leaf margins bear strong spines which are retrorse at the leaf base. The petal appendages consist of a pair of thick, fleshy ridges along the inner edges, overlapping the filaments of the epipetalous stamens, instead of the delicate funnel-shaped appendages of Ananas. The small fruits are low in acid. The plant is resistant to root rot, wilt disease, and fusariosis. It is still exploited in Paraguay, where its name is yvira, which means fiber. According to Collins (1960) some of its characteristics suggest that it could have originated from intergeneric crosses between Ananas and Bromelia, followed by a chromosome duplication. However, P. sagenarius can be hybridized with Ananas but not with Bromelia (Collins, 1949). Pseudananas is more likely to be considered as a neighbor taxon with ancestral characters, as indicated by isozyme studies (Garcia 1988). Initially, this single species was classified as Ananas macrodontes (Morren, 1878), raised to a section by Hassler (1919), to a genus by Harms (1930), and reduced to Ananas sagenaria by Mez (1935) before Camargo (1939) classified it as P. sagenarius. Its distribution is given in Fig. 5.1. According to Camargo (1943), the description by Morren corresponds exactly to P. sagenarius var. macrodontes, found in central Brazil and the coastal areas around Rio de Janeiro, which differs from the numerous varieties described by Bertoni (1919) from the Parana and Paraguay River basins under the name of A. microcephalus. Baker and Collins (1939) could not find materials to support the varieties proposed by Bertoni. On the contrary, they observed very little variation in that area (Smith 1939). Populations of P. sagenarius are rare now because of a very strong reduction of its habitat. However, the few types recently observed by Ferreira et aI. (1992) and by the authors in collections and in the wild (in Paraguay and South Brazil) showed significant variation. The habitat of P. sagenarius is limited to forest areas under semidense shade. It is subjected to a rainy season during most of the year or even to periods of flooding. However, the species is resistant to drought. Baker and Collins (1939) observed P. sagenarius along the Parana and Paraguay Rivers, from north Argentina, just below the confluence of the two rivers, to southern Mato Grosso do SuI. Recent prospections confirm the presence of P. sagenarius populations in those areas, although severely reduced by agricultural and hydroelectric exploitation (Ferreira and Cabral 1993; Duval et aI. 1996). A recent prospection in the southern region of the Bahia state (Ferreira 1996) has also confirmed the presence of P. sagenarius in the residual forests of the eastern coastal region of Brazil, where the species was mentioned by Camargo (1943) and Smith and Downs (1979).


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. ~

4

Fig. 5.1. Distribution of Ananas and Pseudananas. Species are represented by the initial of the species name. S = P. sagenarius (wild); A = A. ananassoides (wild); B = A. bracteatus (cultivated and escapes); F = A. fritzmuelleri (cultivated and escapes); L = A.lucidus (cultivated); N = A. nanus (wild); P = A. parguazensis (wild). Distribution of A. comosus is not indicated because it is found cultivated or as escapes in all tropical lowlands of the continent. Wild A. comosus could not be distinguished from escapes.


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When Charles Plumier (1755) initiated the taxonomic work on the Bromeliaceae during the 16th century, he collected plants called karatas and ananas on the Hispaniola island. The vernacular karatas (and related names as karagwata) is used by the natives throughout South America to name terrestrial bromeliads, in addition to ananas which is used specifically for the pineapple. Following the native classification, Plumier created the genus Bromelia for the karatas in honor to the Swedish physician Olaf Bramel, and described the ananas, using polynomials such as Ananas aculeatus fructu ovato, carne albida (Leal 1989). However, in his Species Plantarum, Linnaeus (1753) designated the pineapple as Bromelia ananas and Bromelia comosa. Lindley (1827) created the genus Ananassa and classified the pineapple as A. sativa. Schultes and Schultes (1830) created the genus Ananas, using A. sativus. Finally, Merrill (1917) established the binomial Ananas comosus based on Linnaeus's Bromelia comosa, synonymous with Bromelia ananas. In 1919, Bertoni divided the genus into five species [A. guaraniticus, A. microcephalus (now P. sagenarius), A. muricatus, A. bracteatus, and A. sativus] with many botanical varieties for each species, which makes it rather confusing. Unfortunately, the material for his study was lost. Smith (1939), with material collected by Baker and Collins, divided the genus into four species, namely A. bracteatus, A. comosus, A. erectifolius, and A. ananassoides. Bertoni's species A. guaraniticus is synonymous with A. ananassoides. In 1943, Camargo added a new species, Ananas fritzmuelleri Camargo, based on specimens collected from southeast Brazil. In 1961, Smith further increased the number of species, with A. nanus (1. B. Smith) 1. B. Smith, formerly considered a dwarf form of A. ananassoides, and A. monstrosus, to designate a crownless pineapple. Camargo and Smith (1968) considered A. parguazensis valid. In 1971, A. erectifolius became a synonym of A. lucidus (Smith, 1971). The last revision was by Smith and Downs (1979), who retained the eight species mentioned. Since then, Leal (1990b) invalidated A. monstrosus, a nomen nudum synonymous of A. comosus, as the absence of crown is not a permanent character. Pineapple taxonomy is not satisfactory yet, and the seven remaining species reported in Table 5.1 could be reduced (Leal and Coppens d'Eeckenbrugge 1996). Instead of producing stolons, Ananas species multiply by suckers (terrestrial and aerial), slips (suckers from the peduncle), and crown. As for Pseudananas, their leaves are densely rosulate and the scape is erect. In A. fritzmuelleri and some A. comosus cultivars, the petals' appendages are similar to those of Pseudananas. The sorose-type fruit is formed by the coalescence of 50 to 200 berries. The highly variable A. comosus is differentiated by its large fruit (more than 15 em for the Smith and Down's


146

Table 5.1. Valid species of the genera Pseudananas and Ananas. Based on Smith and Downs (1979) and Leal (1990b). Scientific Name

Pseudananassagenarius (Arruda da Camara) Camargo Ananas ananassoides (Baker) 1. B. Smith Ananas nanus (L. B. Smith) 1. B. Smith Ananas parguazensis Camargo & L. B. Smith Ananas lucidus Miller Ananas bracteatus (Lindley) Schultes f. Ananas Jritzmuelleri Camargo Ananas comosus (1.) Merrill

Common Name Gravata de cerca, gravata de rede, yvira Ananas de ramosa, curibijul, maya pin6n, nanai, pinuela Ananai Gravata, pina montanera Curagua, curana, curaua, kulaiwat Ananas bravo, ananas do mato Ananas silvestre, gravata de cerca Abacaxi, ananas, pina

key; up to several kilograms in some cultivars) on a wide, short to long peduncle. In the spiny genotypes, the spines are antrorse and generally smaller and denser than in other species. As commonly found in Bromeliaceae, the genus Ananas is diploid, characterized by having 50 minute and almost spherical chromosomes in both root tips and pollen mother cells (Collins and Kerns 1931; Canpinpin and Rotor 1937; Marchant 1967; Sharma and Ghosh 1971; Lin et al. 1987; Brown and Gilmartin 1989; Dujardin 1991). Giant unreduced gametes may appear and produce natural triploids and tetraploids (Collins 1933a, 1960). Most genotypes present reduced fertility and a se1£incompatibility system with considerable variation in its expression (Coppens d'Eeckenbrugge et al. 1993). Ananas ananassoides is the most widespread species, from southern Brazil to Venezuela and Colombia (Fig. 5.1). Although a few genotypes thrive in dense rainforest (in the north of its distribution area), it is generally observed in savannas or in low-shaded forest, growing well on soils with limited water-holding capacity (sand, rocks), and forming populations of very variable densities. Most of these populations are monoclonal, but some are polyclonal with variation of recent sexual origin (Duval et al. 1996). The plant has long and generally narrow leaves and bears a small, globular to cylindrical syncarp on a long and thin peduncle. The fruit is often seedy, and its pulp is white, firm, and fibrous, with a high sugar and acidity content, good flavor and aroma, and a narrow heart. The plant exhibits wilt, nematode, and crown and root rot resistances. Resistance to fusariosis is variable. According to the key, A. ananassoides is distinguished from A. comosus by the size of the


147

fruit (shorter than 15 cm). In the same way, A. nanus is characterized by an even smaller fruit (shorter than 4 cm). In fact, as was formerly proposed by Smith in 1939, A. nanus should be considered a dwarf form of A. ananassoides. It is mostly used as an ornamental. Ananas lucidus is cultivated by the natives in the Orinoco basin and to the north of the Amazon River for its very strong and long fibers, which are used to make hammocks and fishing nets (Leal and Amaya 1991). The dry fibers constitute 6% of the plant weight (Camargo 1943). A.lucidus has never been found in the wild. It is discriminated from A. ananassoides by the absence of spines along the leaf margin. However, spiny types have been observed under cultivation or as mutants in collections. So this difference, which depends on a unique dominant gene (Collins and Kerns 1946), as well as its erect habit related to leaf fibrosity, are only the product of human selection for high yield of easily extractable fibers. Plants are medium sized with erect leaves and with a small very fibrous (inedible) fruit. It is resistant to root rot. Ananas parguazensis is also very similar to A. ananassoides with a difference in the retrorse orientation of some spines and a wider leaf slightly constricted at its base. An anatomical and physiological comparison showed no more differences (Leal and Medina 1995). Its distribution is also limited to the north Amazon (Rio Negro) and Orinoco, with a wider variability in the Orinoco (Duval et al. 1996). It grows in the lowland forests under canopies of variable densities, from clearings or river banks to dense forest. Ananas bracteatus has the same southern distribution area as Pseudananas sagenarius. It is always found cultivated as a living hedge, or for fruit juice, or abandoned in ancient settlements. The plant is very vigorous with wide and long leaves, large spines, and abundant suckering. The inflorescence is characterized by its bright pink to red color and long bracts. The seedy fruit and peduncle are medium sized. (According to the key, the syncarp is more than 15 cm long; however, it is often less.) A. bracteatus is well adapted to cool conditions and altitude (it has been observed at 1000 m). It is resistant to nematodes, root rot, and fusariosis. The variability of this species is very limited. A. Jritzmuelleri is almost identical to A. bracteatus with the same spine orientations as A. parguazensis. The other differences lie in the pale green color of the bracts at maturity and the petal appendages. As these variations are also observed within some other species, the status of A. Jritzmuelleri could be reconsidered, including it in A. bracteatus, as was formerly done by Smith (1939). The Smith and Downs key is not tenable. It is mostly based on quantitative traits (e.g., fruit size), not considering genetic and strong environmental variations. The few discriminant qualitative traits, such as

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presence or absence of spines, only depend on one or two genes (Collins and Kerns 1946). Morphological traits such as petal appendages do not justify the division into species. Indeed, most of the intraspecific variation has been neglected. In recent prospections, intermediate material, combining traits specifically attributed by Smith and Downs to distinct species, could not be identified with this key (Duval et al. 1996). The genus organization should be simplified. A new classification and the resulting key should also take into account reproduction biology and heredity of traits. There are no differences between species either in floral structure and cytology, nor in the chromosome number or breeding system. There are no reproductive barriers as crosses are fully fertile as are "interspecific" hybrids. It seems that despite the geographical differentiation observed in the genus (Duval et al. 1996), no definitive speciation has yet taken place. Indeed, if the species concept is to be narrowly applied, only one species should be recognized. From the standpoint of the plant breeder, all Ananas species belong to the pineapple primary gene pool. The genus was first thought to have originated in the southeast of Brazil, northeast of Argentina and Paraguay (Bertoni 1919; Collins 1960). Later, Leal and Antoni (1981) suggested that the center of origin of the genus should be located in an area within looN to 10 0 S latitude and 55 to 75°W longitude because the flora of this region are endemic and the largest number of species are present. Indeed, there is a wider morphological variation both in wild and cultivated types in the areas at the north of the Amazon River (Orinoco and Rio Negro basins, Guianas) than in the southern areas (Paraguay, Southern Brazil) (Leal et al. 1986; Duval et al. 1996). A. comosus, A. ananassoides (with a wide range of morphological and adaptative variation, from forest types to dry savannas types), A. nanus, A. lucidus, and A. parguazensis plus intermediate types are found in the first area, while the second area is the home for A. comosus, A. ananassoides (savanna types), A. bracteatus-A. fritzmuelleri (with poor morphological variation), and Pseudananas sagenarius, species showing ecological specialization. Molecular studies confirm the observations on morphological variation and geographical distribution and the absence of reproductive barriers (see Leal and Coppens d'Eeckenbrugge 1996). Pineapple cultivation very probably started in the northern area, both A. comosus and A.lucidus evolving from A. ananassoides and/or A. parguazensis, the first by a selection based on large fruit size, high quality (lower acidity), and reduced seediness and the second by a selection for long, fibrous, and smooth leaves. Increased fruit size in A. comosus was related to eye number and size and accompanied by wider leaves, bigger stem, and a shorter and wider peduncle. Sensitivity to natural flowering


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induction was reduced allowing a longer cycle and thence a larger fruit. Cultivation based on asexual propagation and artificial selection of seedless genotypes reduced the natural selective pressure on fertility and reinforced self-incompatibility. Domestication also influenced spininess. In some cases, spininess is suppressed by rare dominant mutations. B. Pineapple Cultivars Numerous cultivars and clones, including smooth and spiny 'Cayenne' clones, 'Queen', and 'Black Antigua' have been the subject of early descriptions and classifications (Griffin 1806; Knight 1822; Munro 1835; Beer 1857). Most of these cultivars have been lost, and only 'Cayenne' and 'Queen' remain of commercial importance today. At present, the base of commercial production is limited to a few cultivars. As these cultivars extensively traveled and have been acclimated in many different countries, they frequently have been renamed. Geographical differentiation, cultivar heterogeneity, and clonal selection also contributed to the confusion. As a result, classification of pineapple cultivars is chaotic. Many different cultivars are known by the same name and many different names may be given to the same cultivar (Johnson 1935, Antoni and Leal 1981; Leal 1990a). And the more widespread the cultivar, the greater the confusion. This is particularly true for the cultivars which are the object of international production and trade: 'Smooth Cayenne', 'Queen', 'Espanola Roja', and 'Singapore Canning' or 'Singapore Spanish'. Burne and Miller (1904) classified the pineapple cultivars grown in Florida in four horticultural groups as "Cayenne," "Queen," "Spanish" (centered around 'Espanola Roja'), and a fourth "miscellaneous" category to include an A. ananassoides genotype, in accordance with the characteristics of the fruit. Py and Tisseau (1965) included 'Singapore Spanish' into "Spanish" and added a "Pernambuco" group. Samuels (1970) used this classification as a basis for describing commercial cultivars. A fifth horticultural group named "Maipure" was added by Leal and Soule (1977) to classify cultivars with smooth "piping" leaves. This group was later renamed "Perolera" by Py et al. (1984) to avoid confusion with other nonpiping genotypes called 'Maipuri' in Guyana. The name "Mordilona", from a species name proposed by Linden (1879) and a botanical variety name used by Camargo (Reyes-Zumeta 1967), has also been used for this group (Cabot 1987). It is worth mentioning that such an authority as Collins (1960), who maintained the largest living collection at that time, never used such classifications, using strictly the term (cultivated) variety in its present sense. Indeed, these horticultural classifications are limiting and confusing. First, they take into account but a small part of the existing variability.

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Many genotypes cannot be classified in the five groups. Second, the various groups correspond to different genetic concepts. Variation in "Cayenne" and "Queen" comes from the mere accumulation of minor somatic mutations. 'Smooth Cayenne' and 'Queen' are cultivated varieties (cultivars) according to the International Code of Nomenclature (LU.B.S. 1980), so they always should be mentioned together with the local name or specific clone by names such as 'Champaka' ('Smooth Cayenne') and 'McGregor' ('Queen'), or 'Champaka Smooth Cayenne' and 'McGregor Queen', unless the variation is clearly visible (e.g., the spiny 'Cayenne Baronne de Rothschild'). That is not the case of the other groups, which gather different cultivars based on the presence or absence of spines and on fruit morphology, without regard to the genetic relationship. So, while cultivars with a conical fruit tend to be classified as "Pernambuco," a wide range of landraces from the western Amazon to the Andes get classified as "Mordilona" because oftheir common "piping" trait (which suppresses spines). This view was confirmed by multivariate analysis of morphological variation in the genus Ananas and studies of the incompatibility phenotypes within the so-called groups, which showed the heterogeneity of the groups '~Spanish," "Pernambuco," and "Mordilona," as compared to the cultivars 'Smooth Cayenne', 'Queen', 'Singapore Spanish', 'Espafiola Roja', and 'Perolera' (Duval and Coppens d'Eeckenbrugge 1993; Coppens d'Eeckenbrugge et al. 1996). In conclusion, given their lack of genetic base and the continuous and very wide variability to be described, the classifications into horticultural groups are not adequate and this review will only consider cultivars. 'Smooth Cayenne' is the pillar of the world pineapple industry. It was collected by Perrottet in 1819 in French Guyana under the name "Maipuri" (Perrottet 1825), which means tapir, and is still used for 'Smooth Cayenne' and many large-fruited cultivars in the Guianas and south of the Orinoco. After its transfer to the Kew Botanical Gardens, it was renamed 'Kew' or 'Giant Kew', a name still in use in some former British colonies. In Malaysia, 'Smooth Cayenne' was called 'Sarawak'. An early spiny mutant, 'Baronne de Rothschild', has been cultivated in West Africa. Many strains were given particular names, including 'Champaka', 'Hilo', 'Esmeralda', 'Claire', 'Typhoon', and 'Saint Michel'. Many selected clones have diffused from the PRI and are still used by the ex-member companies in Hawaii and other countries. The 'Smooth Cayenne' monopoly is clearly due to its high yielding potential and good characteristics as fresh fruit as well as for canning. The plant is medium sized (80 to 100 cm), with 60 to 80 dark green leaves (ca. 100 cm long and 6 cm wide) whose smooth margins only bear a few spines at their base and near the tip. The peduncle is short. The fruit is medium sized (1.5 to 2.5 kg), ovoid,


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and green with yellow base at maturity. Its tasty pale yellow flesh is juicy, with higher sugar (variable, 13 to 19° Brix) and acid content than most other cultivars. But it is fragile and much poorer in ascorbic acid. It is sensitive to many known pests and diseases and is a poor producer of planting stock, particularly basal slips. 'Singapore Spanish' is second in importance for canning. It is mainly cultivated in south Asia countries, particularly in Malaysia because of its good adaptation on peat soils and its golden yellow flesh color. In this country, 'Singapore Spanish' strains are known under such diverse names as 'Singapore Canning', 'Ruby', 'Red Pine', 'Nanas Merah', 'Nangka', 'Gandol', 'Betek', and 'Masmerah'. An anthocyanless cultivar was derived by mutation, and its strains designated as 'Green Pine', 'Selangor Green', 'Nanas Hijau', 'Green Spanish', and 'Selassie' (Wee 1972). Old Taiwanese clones are' Anpi', 'Oohi', and 'Uhi' (Sakimura 1935). The plant of 'Singapore Spanish' is medium sized (80 to 100 cm) with 35 to 70 dark green leaves, the longest reaching a length of 150 cm and a width of 5 em. Spininess is variable, from complete spininess in some clones to a very few spines near the leaf tip in others. The peduncle and inflorescence bracts are deep, bright red. Fruits are small (under or around 1 kg, heavier in 'Masmerah'), cylindrical, and a dark purple that turn reddish-orange with ripening. Anthocyanless strains, with light green leaves and heart, produce green fruits that turn yellow at maturity. The bright yellow flesh tastes poor, because of low Brix (10 to 12°) and acidity. The plant is vigorous with regular production of slips (about 2 to 6) and suckers. Multiple crowns are frequent. It is tolerant to stress and most common diseases and pests. The nomenclature of 'Queen' strains was also diversified in Asia, with names such as 'Mauritius', 'Malacca', 'Red Ceylon' (Leal 1990a), and 'Buitenzorg' (Mendiola et al. 1951). It has also been cultivated extensively in South Africa and Australia for the fresh fruit market. 'Ripley Queen', 'Alexandra', and 'McGregor' are some of the selections made by Australian growers. The tetraploid 'Z' or 'James Queen' cultivar was found in South Africa (Nyenhuis 1974). 'Panare', a cultivarvery similar to 'Queen', exists in the Orinoco basin (Leal and Antoni 1980). The plant of 'Queen' is small (60 to 80 cm), with short and very spiny, silvery leaves. The fruit is too small for canning (0.5 to 1 kg), with full yellow shell and small prominent eyes. Its golden yellow flesh is crisp and sweet (14 to 17° Brix), low in acid, with excellent flavor and long shelf life. Slip production is very variable and dependent on the particular clone. The cultivar is more tolerant to stress and diseases than' Smooth Cayenne'. 'Espanola Roja' ('Red Spanish') originates from Venezuela and the Caribbean basin where it is still cultivated. Synonyms are 'Black Spanish',

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'Key Largo', Havannah' or 'Habana', 'Cubana', 'Cowboy', 'Bull Head', and 'Native Philippine Red' (Leal 1990a). 'Espanola Roja' plants are medium sized with dark green leaves which are either spiny or partially spiny. As in 'Singapore Spanish', floral bracts are of an intense bright red color. The medium-sized fruit (1.2 to 2 kg) is barrel shaped. The white or pale yellow flesh is juicy and tastes sweet (although only around 12° Brix) because of low acidity. Aroma is strong and pleasant. The plant regularly gives a few slips (1 to 3) and suckers. It is vigorous and tolerant to stress and common diseases, but not to the fruit borer Thecla basilides Geyer. 'Perola' is the main Brazilian cultivar. It is also known as 'Pernambuco' or 'Branco de Pernambuco' in Brazil, but it was named 'Abacaxi', 'Abakka', or 'Eleuthera' in Florida. 'Jupi' is the name for a particular 'Perola' strain. 'Perola' plants are medium sized, erect, and very vigorous, with dark green spiny leaves. The fruit, only used in the fresh market, is small to medium (0.9 to 1.6 kg), conical and green with a little yellow at maturity. The flesh is white and juicy with a high sugar content (13 to 16° Brix), low acidity, and a pleasant aroma. The plant shows tolerance to stress, mealybug wilt, and nematodes, but it is highly susceptible to fusariosis. 'Perolera' is a local cultivar in Colombia and Venezuela, adapted to high altitude (up to 1,500 m). It is also known as 'Lebrija', 'Motilona', 'Capachera', or 'Tachirense'. The plant is medium to high, with procumbent leaves which are completely spineless as the lower epidermis is folded over the leaf edge, a trait which was named "piping" by Collins and Kerns (1946). The peduncle is very long and the large cylindrical fruit (1.5 to 3 kg) frequently lodges, provoking fruit sunburn. Shell color varies from yellow to orange. The flesh is pale yellow to yellow, sweet (although Brix is around 12°), tender, and firm. Numerous crownlets protrude frOITl the base of the crown or from the upper eyes. Slips are numerous (commonly 4 to 11). Plants are able to grow in poor conditions. In particular, this cultivar is resistant to fusariosis. The cultivar 'Bumanguesa', also called 'Manzana', which produces a very attractive bright red fruit with large flat eyes and regular shape, is considered a selected mutant of 'Perolera'. The six best-known cultivars described here only constitute a small sample of the available germplasm. Other cultivars are only cultivated in small holdings in tropical America, such as 'Cabezona' in Puerto Rico, a spiny vigorous natural triploid producing yellow-orange fruits of more than 3 kg with white pulp; 'Monte Lirio' ('Cambray', 'Milagrena'), a smooth (piping) cultivar from Mexico to Ecuador, producing a medium-sized yellow pineapple with a sweet white pulp; 'Black Antigua', a spiny cultivar from the Antilles (well known by the first


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European growers), producing a small to medium, green and yellow to orange fruit with a delicious firm golden yellow pulp; the Peruvian 'Samba' whose medium-sized red fruit is resistant to the penetration borer insects as Thecla basilides and fruit flies; and the Brazilian 'Branco' with light green leaves and a green and yellow, medium to large fruit with white flesh. Many other interesting cultivars, particularly from the most distant areas of the Amazon and Orinoco basins, have been neglected so far, mainly because they are more difficult to access. Some parts of these areas have only been prospected recently and much remains to be done. C. Mutations in Pineapple

The natural breeding system of Ananas is based on sexual reproduction and clonal propagation. Vegetative propagation is the dominant form of reproduction because of the vigor and desiccation resistance of the various kinds of vegetative propagules as compared to the slow germination and fragility of young seedlings. Present-day pineapple cultivars originated well before the Spanish conquest. Since then, they have been subjected to a permanent mutation/selection process, whose effects cannot be neglected on such a time frame. As a result, most cultivars have diversified into a collection of phenotypically similar clones. Collins and Kerns (1938) reported as many as 30 qualitative morphological mutations in 'Smooth Cayenne' concerning floral traits (color, exuberance), fruit characters (Bottle Neck and Dry Fruit inhibiting fruitlet development; Crowning Beauty inducing a vegetative reversion of flowers; Big Eye enlarging fruitlet size; Rough Eye; Slender Fruit and Elongated Fruit; Seedy Fruit, a mutation breaking down self-incompatibility in pollen), vigor, spininess, trichome suppression, chlorophyll and anthocyanin mutations, and Collar-oj-Slips. Seedy Fruit, Collar-oj-Slips, Crowning Beauty, and two mutations affecting vigor are dominant, while the mutations involving spiny leaves, loss of anthocyanins, and loss of chlorophyll are recessive to the normal characters. White Flowers is codominant. Wee (1979) listed similar mutations in Malaysia, in 'Singapore Spanish' and 'Selangor Green' (a green mutant of 'Singapore Spanish') and in 'Mauritius' ('Queen'). The frequency of mutations is difficult to determine as a mutated sector may be borne by an apparently normal chimeral plant. However, Collins (1960) could determine that the somatic mutation rate for spininess is around 6.8% in heterozygous hybrids, which is unusually high. Singh et al. (1976; 1979) also found unusual rates, between 0.06 and 0.11 %, in a 'Kew' ('Smooth Cayenne') population. In contrast, the reversion from the spiny to the smooth condition is

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extremely rare. An interesting mutation is Mealybug Wilt Resistance reported by Collins and Carter (1954) in Hawaii and by Torres Navarro et al. (1989) in Mexico. Other mutations affect quantitative traits, thus producing continuous variation. They are difficult to detect as their expression also depends on the environment. This is the case of the mutations affecting the number of slips and the presence of knobs on the fruit (different from Collar-oj-Slips), multiple crowns, and fruit fasciation (Dalldorf, 1975a,b). A given mutation may appear more frequently in certain cultivars. For instance, multiple crown is exceptional in 'Queen' while it is common in 'Smooth Cayenne' and' Singapore Spanish.' With the exception of Wilt Resistance, Seedy Fruit, and some mutations affecting the pigmentation of the plant and fruit, which may make it more attractive, no mutations have potential implication for breeding. On the contrary, their accumulation produces an undesired intracultivar variability, so imposing a constant clonal selection effort to the producer, the horticulturist, the breeder, and the germplasm bank curator. As a result of constant clonal selection, by eliminating deleterious mutations, the potential of 'Smooth Cayenne' has been maintained at a high level. In some cases, the adaptation of the crop to specific conditions may have been improved through the selection of minor mutations for quantitative traits. In the other cultivars, the greater variability is mostly the result of the accumulation of negative traits such as multiple crowns and spininess because clonal selection has been neglected in these secondary cultivars. Many cultivated clones of 'Espafiola Roja' and 'Singapore Spanish' reverted to the spiny condition and even such important cultivars as 'Singapore Spanish', 'Perola', and 'Perolera', although well adapted to the conditions of important local markets and/or zones of production, strongly suffer from defects such as a proliferation of crowns and slips. III. PROBLEMS OF GENETIC SIGNIFICANCE

A. Fertility and Incompatibility Fertility and self-incompatibility must be taken into account in a breeding program as pineapple cultivars must be highly self-sterile to be commercially successful. Most pineapple cultivars set no seeds when grown alone, but they can set seeds if different cultivars are grown side by side, as is the case in a germplasm collection. The absence of seeds in monocultivar cultivation is due to self-incompatibility. Fertility is low in A. comosus. As expressed by the percentage of ovules producing a seed after open pollination, it is less than 5 % (less than 2


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seeds per flower) in 'Cayenne', 'Espanola Roja', 'Singapore Spanish', 'Perola', and 'Queen', and 4 to 11 % (2 to 5 seeds per flower) in the genotypes with "piping" leaves. The highest fertility value in A. comosus was reached by the clone GU47 (29%). With the exception of a few triploid clones, other species show higher fertility although many of them have fewer ovules per flower. Their fertility ranges from 6% in A. nanus to 35 to 45% in the most fertile clones of A. ananassoides, A. parguazensis, and A. bracteatus. Fertility is correlated with the proportion of ovules containing an embryo sac (r = 0.75; n = 14), the logarithm of pollen stainability (r= 0.59; n = 71), and the amount of pollen produced per flower (r = 0.71; n = 71). It is not correlated with ovule number (r =-0.06; n = 71), which could be explained by crowding or competition effects between fertilized ovules. Many A. comosus and A. bracteatus genotypes can develop but a small proportion of their numerous ovules (up to 70 per flower) into seeds (Coppens d'Eeckenbrugge et al. 1993). The self-incompatiblity reaction in pineapple is due to the inhibition of pollen tube growth in the upper third ofthe style, generally on the stigmatic lobes (Kerns 1932; Majumder et al. 1964). Brewbaker and Gorrez (1967) showed that it is gametophytically controlled by a single locus with multiple alleles. Self-incompatibility is generally considered to be characteristic of the cultivated A. comosus but it prevents or reduces selffertilization rates in all the Ananas species. In a study of 71 clones from all the species but A. fritzmuelleri, Coppens d'Eeckenbrugge et al. (1993) only found full self-compatibility in three clones of A. bracteatus var.bracteatus. Since then, self-compatibility has also been found in a clone of A. parguazensis. Pseudo-self-compatibility, expressed by partial self-fertility, is found in clones from A. comosus, A. ananassoides, A. parguazensis, and A. bracteatus. Pseudananas sagenarius is self-fertile; selfprogenies are homogeneous, suggesting that this species is homozygous and autogamous. In natural conditions, this species is largely reproduced by seeds (Collins 1960). Pseudo-compatibility is less frequent and less marked in A. comosus, probably because strong self-incompatibility was selected by man as a supplementary seediness-reducing factor. 'Smooth Cayenne', 'Espanola Roja', most 'Queen' clones, and 'Black Antigua' are self-sterile. Pseudoself-compatibility occurs in some clones of 'Singapore Spanish' and is common in 'Perolera', 'Manzana', 'Primavera', 'Samba', and 'Alto Turi', allowing some self-fertility. Pseudo-self-compatibility results from a weakening of the self-incompatibility reaction, which is generally attributed to minor modifying genes. Variation for this trait is continuous between cultivars and between clones from the same cultivar. Hybrids should be carefully assessed for this trait, even if none of the parents is

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pseudo-self-compatible. Pseudo-self-compatibility can be used when inbreeding is desired in breeding programs (Leal and Coppens d'Eeckenbrugge 1996). In the same sense, Collins (1960) used the dominant Seedy Fruit mutation conferring full self-compatibility to 'Smooth Cayenne'. The segregation in the progeny provides for recovery of selfincompatible hybrids. No interspecific incompatibility has been observed in the genus Ananas, neither at the level of pollen-pistil interaction nor in embryogenesis and seed development. Interspecific crosses involving A. comosus are at least as fertile as intercultivar crosses, and the hybrids are fertile. When A. comosus is crossed with Pseudananas sagenarius, a few fertile seeds are produced. Hybrids are tetraploid, vigorous, highly fertile, and self-fertile. Similarly, crossing P. sagenarius with other Ananas species produces a majority of tetraploids and some smaller and self-sterile triploids (Collins 1960). Thus, there are no biological limitations to the exploitation of genetic resources in the genera Ananas or Pseudananas. B. Environmental Adaptation Although Ananas evolved under very rainy conditions, it developed xerophytic characteristics, as in other genera of the Bromeliaceae. This is probably related to the high drainage capacity of the sandy and rocky soils of its original habitat. All pineapple germplasm may be considered resistant to drought. No systematic comparisons of cultivars have been conducted, but field observations suggest that 'Perola' and 'Espanola Roja' are more resistant than 'Smooth Cayenne'. Most A. ananassoides genotypes, which inhabit dry regions in the cerrados of central and south Brazil, or live on pure sand soils and on rocks in the rainforest, show a particularly high level of resistance. In contrast, no pineapple germplasm is tolerant to flooding, with the exception of Pseudananas sagenarius. Pineapple germplasm is more variable in its adaptation to open or shaded areas. It normally grows in rather open areas, although some genotypes thrive under the shade of the dense rainforest. However, even these forest genotypes grow well in sunny conditions, showing shorter and wider leaves. The pineapple demands soils with good drainage, because it is very sensitive to anoxy. It is best suited to acid soils with either sandy, sandy loam, or clay loam texture. Certain cultivars, such as 'Queen', show more tolerance to water logging (Bartholomew and Malezieux, 1994). Pineapple is also sensitive to high manganese concentration in the soil, which interferes with iron metabolism in the plant and provokes chloro-


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sis. 'Espanola Roja' and 'Singapore Spanish' are particularly susceptible, while 'Smooth Cayenne' and 'Perola' appear tolerant. On the other hand, 'Singapore Spanish' is particularly adapted to peat soils (Chan and Lee 1985). Adaptation to high pH is probably related to tolerance to Phytophthora as this fungus develops better and is more aggressive in such conditions. Temperature requirements of cultivated pineapple are typical of tropical crops. Some areas of cultivation present limiting conditions, particularly in the subtropics or in high altitudes, concerning the length of the cultivation season and/or extreme seasonal temperatures. This can affect the length of the cultivation cycle, fruit size, and quality. The production cycle of 'Smooth Cayenne' is particularly long and fruits are acid and poor in sugar when grown under cool conditions, but quality is also reduced under very hot and humid climates (Bartholomew and Malezieux 1994). Other cultivars, such as 'Queen', can better support cool conditions with more stable fruit quality. In the Andes, cultivars better adapted to altitude, such as 'Perolera' 'Manzana', 'Valera Amarilla', and 'Valera Roja' are grown above 1,000 m. Fruit color seems enhanced with high altitude, probably as a result of higher radiation. 'Espanola Roja' is tolerant to high temperatures. Plant morphology is important in the response of the plant to temperature and radiation. Cultivars with a strong peduncle are less exposed to fruit lodging and sunburn. C. Propagation Adaptability

Ananas ananassoides and A. parguazensis are very efficient in their vegetative propagation, multiplying from the stem base by suckers and, after lodging, from the peduncle slips and from the crown. This potential has been well preserved in the domesticated species. Suckering is still important in A. bracteatus-A. fritzmuelleri and particularly spectacular in A. lucidus. In A. comosus, cultivars and clones differ widely in the types and number of propagules produced. Variation is particularly important in the number of slips as grower needs vary with their production system. 'Smooth Cayenne' produces a few suckers with a very variable number of slips. Under intensive cultivation, the ideotype is a plant which very regularly produces one or two early suckers from the base of the stem near or in the ground, thus allowing for a fast and uniform second harvest (whose production is lower but much less expensive). With good homogeneous material, even a third harvest is possible. Crowns are the most frequent planting material for production destined for canning. Multiple crowns must be avoided as they are correlated with a wide core and associated with fruit fasciations. Modern

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'Smooth Cayenne' clones have been selected to produce very few slips, as their removal requires additional work. In addition, although they are available much earlier than suckers, at fruit harvest their early growth is slower, lengthening the whole production cycle. On the other hand, 'Smooth Cayenne' populations producing many slips (up to a dozen) still exist. Farmers in the developing countries prefer such genotypes because they allow rapid expansion of the cultivated areas and thus more adaptability to market conditions. In any case, collar-of-slips (too many slips at the base of the fruit) must always be eliminated as it is related to a widening of the core. The relationship between the number of slips and fruit size has never been clearly established. On the one hand, the fruit might suffer from competition between these organs for available resources. On the other hand, large fruits and collar-of-slips are frequently associated on vigorous plants, possibly because both are positively affected by plant vigor. As cultivars other than 'Smooth Cayenne' are frequently cultivated under less intensive conditions (maximum densities of 40,000 plants/ha instead of more than 60,000 for 'Smooth Cayenne'), they have been less selected to control propagation capacity. The plants are sometimes left in the field for further harvests, forming dense tufts after several cycles, until the fruits are too small to be marketed. But excessive suckering may be a problem in modern cultivation, particularly with some strains of 'Queen' and 'Espanola Roja.' Slips are frequently used as planting material and their prolificity is appreciated. Some 'Perola' strains have a collar oflong erect slips that almost surrounds the fruit, which is sometimes harvested together with it, ensuring protection of the fruit during transportation. 'Singapore Spanish' strains often suffer from multiple crowns. This heritable defect is also common in 'Perolera', 'Manzana', and many minor cultivars such as 'Samba', which presents a problem when using such cultivars in breeding. It is less of a problem in 'Espanola Roja', 'Primavera', and 'Roxo de Tefe'. Multiple crowns are frequent in the species A. ananassoides, A. bracteatus, and A. lucidus. D. Productivity Productivity is a complex trait in pineapple as this concept integrates saleable fruit yield, processing yield (related to fruit shape and size), length of cultivation cycle (which depends on the genotype, its suckering habit, climate, and time of flowering induction), homogeneity, and eventual ratoon crops (with shorter cycles and lower production cost). Shape parameters are also important in determining the industrial yield. Once more, 'Smooth Cayenne' is the reference as it can produce medium


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to large fruits at very high densities under intensive cultivation. Comparisons with other cultivars are difficult because of the difference in cycle length and because of the very different technical conditions under which they are generally grown. In a few cases, however, two cultivars cultivated in the same region may be compared, at least on the most obvious component of productivity, fruit weight. Data from the Martinique germplasm collection, where all genotypes are cultivated with the same techniques, also allow some comparisons although the production system was specifically designed for' Smooth Cayenne'. With the exception of 'Perolera', none of the five other major cultivars compares with 'Smooth Cayenne'. 'Espafiola Roja' is slightly smaller, then comes 'Perola', and finally 'Singapore Spanish' and 'Queen'. Variations between clones from the same cultivar may be important as the fruit weight of the best clone may be double that of the poorest clone. So the importance of the particular clone cannot be neglected as a 100-g variation in fruit weight between two clones translates to tons/ha at the field level. Some minor Amazonian cultivars ('Gigante de Tarauaca', 'Cabe50 days) was obtained. However, a low level of expression was reported, and blackheaded fireworm larva feeding bioassays did not indicate a high efficacy level. Meristem tissue culture methods have been developed and are considered routine (Scorza et al. 1984; Scorza and Welker 1988; Marcotrigiano and McGlew 1991; Serres and McCown 1994). Serres and McCown (1994) reported a method for flower bud induction in tissue-cultured plants that could be used to facilitate biotechnology, breeding, and physiological studies. Adventitious shoot formation from leaf tissue has been reported (Marcotrigiano et al. 1996), indicating that somaclonal methods may be possible for genetic enhancement, but evidence for somaclonal variation is limited. IV. ENVIRONMENTAL ISSUES The major environmental issues faced by cranberry growers are all related to the sensitive wetland areas in which cranberries are grown. These issues are similar to those faced by any industry wishing to develop wetlands such as water levels, wildlife populations, endangered species, habitat loss, and pesticides in the environment. The native habitat for cranberries is wetland areas (Vander Kloet 1988). In the United States, wetlands are protected under federal legislation that is administered by the U.S. Army Corps of Engineers. In a recent analysis, the Corps of Engineers has determined that cranberry farming is a water-dependent activity (U.S. Army Corps of Engineers 1995). This is significant because it shifts the burden of proof to show that no practicable alternatives exist from landowners to the agency. However, applicants do have to show that any activity in wetlands will have the least possible adverse effects. Individual states may also have their own wetland regulations that must be met before construction in wetlands can begin.

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A. Water Use Water is essential for cranberry production. Water is used for frost protection, to replace evapotranspiration, to cool vines on hot summer days, as a harvest aid, and in the winter to protect against desiccation and freeze injury. Large quantities of water may be used in cranberry production. The U.S. Army Corps of Engineers estimates that in Wisconsin 3155 m 3 of water is used per hectare of planted vines each year (U.S. Army Corps of Engineers 1995). Until the 1960s, it was common practice for cranberry growers to flood irrigate to replace evapotranspiration (Davies and Darnell 1994). Flooding required large quantities of water, especially if beds were not level. Since the 1960s, most North American growers irrigate with sprinkler irrigation. The change to sprinkler irrigation greatly reduced water use by cranberry growers. Uniformity of sprinklers can be improved by making sure the uprights are perfectly vertical, by replacing worn nozzles, and by increasing riser length to at least 30 cm above bed height (T. Bicki, pers. comm.). Sprinklers are also used for frost protection and evaporative cooling. Because cranberries do not grow in standing water and will not tolerate long flooding durations during the growing season, and because large amounts of water are applied to cranberry beds, drainage is a constant process so it is possible for pesticides to leave cranberry marshes in drainage water. This is most common when a pesticide application is closely followed by rainstorms. Tailwater is frequently discharged into wetlands and other sensitive environmental areas. Pesticide labels require water to be held in beds for a certain amount of time before discharge to allow pesticide degradation to allowable levels. It is incumbent on growers to limit, in so far as possible, discharges of pesticides from beds. Growers are experimenting with treating drainage water with activated charcoal or discharging into constructed wetlands to ensure that as little pesticide as possible will leave treated areas.

B. Wildlife Roughly 10 ha of support land is owned and maintained by Wisconsin Cranberry Growers for every hectare of planted cranberries (Jesse et al. 1993). Numerous species of wildlife use the support lands as habitat. The actual presence of cranberry beds does limit species diversity. Jorgensen and Nauman (1994) found that the importance value ofpteridophytes increased as distance from planted areas increased. Species found close to beds usually had an affinity for sand and dry conditions.

7. CRANBERRY: BOTANY AND HORTICULTURE

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They made the suggestion that dikes and roadways be vegetated to be more inviting to a broader array of species than bare areas. Ellsworth and Schall (1991) reported observing 64 bird, 4 reptile, 14 mammal, 2 amphibian, and 11 fish species at three Wisconsin cranberry marsh sites. At three cranberry sites in Massachusetts, they found 65 bird, 6 reptile, 11 mammal, 7 amphibian, and 11 fish species. As would be expected, they found low wildlife diversity in active cranberry beds, but great diversity in associated reservoirs and wetlands. While cranberry plantings affect wetlands, not all effects are negative. C. Environmental Pesticide Residues

Pesticide use in cranberry production is a difficult issue, especially because cranberries are grown in environmentally sensitive areas. In Massachusetts, Deubert and Kaczmarek (1989) measured residues in cranberry effluent water. They found that 90% of parathion breakdown in ditchwater occurs in the first two to four days following application and during this time water is held on beds and not discharged. Parathion levels in bed discharge water ranged from 0.11 to 5.8 ppb, with a mean of 1.12 ppb. These levels decreased slightly to a range of 0.21 to 0.93 ppb, mean 0.39 ppb, by the time the water left the watershed. During their study under Massachusetts conditions, only 45.8 g/day parathion was discharged by a watershed. It is no longer legal to apply parathion to cranberries in the United States. In Canada, Szeto et al. (1990) found Diazinon residues declined from 456 ppb in irrigation ditch water within the treated bed just following application to 45.2 ppb in the same location seven days later. By three weeks after treatment, no detectable residues were found in ditch water. Very low levels «60 ppb) were found in adjacent waterways. However, they did find that residues accumulated in the sediments of ditches within the beds where four days after an application 21,200 ppb were found. At two weeks after application, fruit had residues of 12 ppb, well below the tolerance of 250 ppb. At three weeks after application, Diazinon residues had declined to 6 ppb. Residues continued in these sediments up to 19 weeks after treatment. Vertical movement of parathion was examined in the sandy soils of the New Jersey "Pine Barrens." Because parathion is not very soluble in water, no vertical movement of parathion was detected (Winnett et al. 1990). This suggests that parathion residues occasionally found in water samples in that location are unlikely to be from cranberry cultivation. Spray adjuvants were found to reduce off-target deposition of pesticides by about 80% when applied by helicopter or through chemigation

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(Clark at al. 1993). Reductions were found in both the particulate and vapor phaf:e residues. While pesticides are necessary to cranberry production today, the total environmental load does not seem extreme where studied. Growers and advisors must strive to minimize pesticide applications and to make necessary applications on target.

V. FUTURE PROSPECTS The cranberry industry has withstood numerous difficulties since its beginning. Early growers faced uncontrolled flood or drought, fire, uncontrollable pests, and isolation. Growers sought to improve the prices they received through cooperative marketing. The aminotriazole debacle of the late 1950s, while difficult at the time, unified the industry and led to the realization that cranberry marketing could not be a seasonal endeavor but that year-round markets for high-quality products had to be established. Ocean Spray Cranberries, Inc., is now a leading manufacturer and distributor of high-quality brand-name products derived from cranberries. Until recently, the cranberry industry was pretty much restricted to five states and three Canadian provinces in North America. Commercial cranberry plantings are established and expanding in Michigan and Maine, and there is interest from other states as well. Plantings in Canada are expanding rapidly. There is also great interest outside of North America. As of this writing, over 300 ha of cranberries have been planted in southern Chile with an additional 300 ha planned before the turn of the century. Plantings are also being made in Europe. About 5 ha were harvested in Ireland in 1995. Small initial plantings are being made in former Soviet Republics such as Estonia, Lithuania, and Latvia and many suitable sites exist in Russia and Poland. Most of the new plantings in the United States are established in upland locations to avoid the lengthy and expensive permitting process to develop wetlands. Problems still remain to be overcome in upland sites. Holding water during the winter to protect vines is perhaps the most difficult obstacle. Other problems and potential problems include retaining nutrients and pesticides in the root zone and keeping them out of ground and surface waters, temperature management, and overall water management. Given the resourcefulness of growers and researchers, these problems can be overcome. Research needs include nonchemical pest management, continued exploitation of the genetic resources for yield improvement and pest resistance, propagation and planting technology, better understanding


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of cranberry physiology and how it relates to management, and winter management. With continued industry support for research, this agenda can be accomplished. As the turn of the century approaches, the outlook for the cranberry industry is bright. The price received exceeds the cost of production and the market for cranberry products appears to exceed supply. Creative product development has resulted in an increasing demand for cranberries for a variety of products, and a bright future for this native American fruit. This is the legacy of cranberry pioneers who had the foresight and vision to work together and to create marketable products from the small, tart berries.

LITERATURE CITED Anonymous. 1959. Unexpected marketing crisis rocks the entire industry. Cranberries Mag. 24(9):11-13. Anonymous. 1995. U.S. bottler backs European production. Cranberries Mag. 59(11):5, 21.

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Roper, T. R, K. D. Patten, C. J. DeMoranville, J. R Davenport, B. C. Strik, and A. P. Poole. 1993. Fruiting of cranberry uprights reduces fruiting the following year. HortScience 28:228. Roper, T. R, P. Skroch, and J. Nienhuis. 1995b. Barren berry and Searles vines are genetically dissimilar. Cranberries 59(3):14-15. Rosen, C. J., D. 1. Allen, and J. J. Luby. 1990. Nitrogen form and solution pH influence growth and nutrition of two Vaccinium clones. J. Am. Soc. Hort. Sci. 115 :83-89. Sapers, G. M., J. G. Phillips, H. M. Rudolph, and A. M. Divito. 1983. Cranberry quality: selection procedures for breeding programs. J. Am. Soc. Hort. Sci. 108:241-246. Sapers, G. M., S. B. Jones, M. J. Kelley, and J. G. Phillips. 1986. Breeding strategies for increasing the anthocyanin content of cranberries. J. Am. Soc. Hort. Sci. 111:618-622. Sarracino, J. M., and N. Vorsa. 1991. Self and cross fertility in cranberry. Euphytica 58:129-136. Schmid, P. 1977. Long-term investigation with regard to the constituents of various cranberry varieties. Acta. Hort. 61:241-254. Scorza, R, and W. V. Welker. 1988. Cranberries (Vaccinium macrocarpon Ait.) p. 199-208. In: Y. P. S. Bajaj (ed.), Biotechnology in agriculture and forestry. VoL 6, Crops II. Springer-Verlag, New York. Scorza, R, W. V. Welker, and 1. J. Dunn. 1984. The effects of glyphosate, auxin and cytokinin on in vitro development of cranberry node explants. HortScience 19:66-68. Serres, R, and B. McCown. 1994. Rapid flowering of microcultured cranberry plants. HortScience 29:159-161. Serres, R, E. Stang, D. McCabe, D. Russell, D. Mahr, and B. McCown. 1992. Gene transfer using electric discharge particle bombardment and recovery of transformed cranberry plants. J. Am. Soc. Hort. Sci. 117:174-180. Shawa, A. Y., C. H. Shanks, P. R Bristow, M. N. Shearer, and A. P. Poole. 1984. Cranberry production in the Pacific Northwest. Extension Bulletin PNW247. Washington State Univ., Pullman. Sirois, G. 1994. Cranberry pioneers of the Fraser Valley. Cranberries Mag. 58(3):16-20. Smith, J. D. 1994. Nitrogen fertilization of cranberries: What type should I use, how should I apply it, and where is my nitrogen from last season? Proc. Wisconsin Cranberry School 5:23-30. Sobota, A. E. 1984. Inhibition of bacterial adherence by cranberry juice: potential use for the treatment of urinary tract infections. J. Urology 131:1013-1016. Stang, E. J., C. Plowright, and D. L. Mahr. 1992. A survey of field activity and influences of commercially reared bumble bee (Bombus spp.) on pollination, fruit set and productivity in cranberry. Proc. Wisconsin Cranberry School 3:1-7. Steiber, T., and L. A. Peterson. 1987. Contribution of endogenous nitrogen toward continuing growth in a cranberry vine. HortScience 22:463-464. Stevens, N. E., and J. Nash. 1943. The development of cranberry growing in Wisconsin. Wisconsin Mag. History 27:276-294. Stewart, C. N. Jr., and E. T. Nilsen. 1995. Phenotypic plasticity and genetic variation of Vaccinium macrocarpon, the American cranberry. 1. Reaction norms of clones from central and marginal populations in a common garden. Int. J. Plant Sci. 156:687-697. Strik, B. c., and A. Poole. 1991. Timing and severity of pruning effects on cranberry yield components and fruit anthocyanin. HortScience 26:1462-1464. Strik, B. c., and A. Poole. 1992. Alternate-year pruning recommended for cranberry. HortScience 27:1327. Strik, B. C., and A. Poole. 1995. Does sand application to soil surface benefit cranberry production? HortScience 30:47-49.


249

Strik, B. c., T. R. Roper, C. J. DeMoranville, J. R. Davenport, and A. P. Poole. 1991. Cultivar and growing region influence return bloom in cranberry uprights. HortScience 26:1366-1367.

Szeto, S. Y., M. T. Wan, P. Price, and J. Roland. 1990. Distribution and persistence of diazinon in a cranberry bog. J. Agr. Food Chern. 38:281-285. U.S. Army Corps of Engineers. 1995. St. Paul district analysis regarding section 404 review of commercial cranberry operations. Vander Kloet, S. P. 1983. The taxonomy ofVaccinium and Oxycoccus. Rhodora 85:1-44. Vander Kloet, S. P. 1988. The genus Vaccinium in North America. p. 107-114. In: Res. Branch Agr. Can. Publ. 1828. Vorsa, N. 1987. Characterization of pollen stainability and seed set in cranberry. HortScience 22:380 (Abstr). Winnett, G., P. Marucci, S. Reduker, and C. G. Uchrin. 1990. Fate of parathion in ground water in commercial cranberry culture in the New Jersey Pinelands. Bul. Environ Contam. Toxicol. 45:382-388.

Subject Index

o

c Cranberry, botany and horticulture, 215-249

Okra, botany and horticulture, 41-72 Olive, salinity tolerance, 177-214

D

p

Dedication, Sherman, W.B., xi Deficit irrigation, 105-131

Physiology, olive salinity tolerance, 177-214

Pineapple, genetic resources, F

138-141

Fruit crops: cranberry, 215-249 deficit irrigation, 105-131 irrigation, deficit, 105-131 olive salinity tolerance, 177-214

s Salinity, olive, 177-214 Sorghum, sweet, 73-104 Stress, salinity tolerance in olive, 177-214

G

v

Genetics and breeding: pineapple, 138-164 sweet sorghum, 87-90 Germplasm preservation, pineapple, 164-168

Germplasm resources, pineapple,

Vegetable crops: greenhouse management, 1-39 okra, 41-72

w

133-175

Greenhouse and greenhouse crops, vegetables, 1-39

Water relations, deciduous orchards, 105-131

I

Irrigation, deficit, deciduous orchards, 105-131

251

Cumulative Subject Index (Volumes 1-21) A Abscisic acid: chilling injury 15:78-79 cold hardiness, 11:65 dormancy, 7:275-277 genetic regulation, 16:9-14, 20-21 mechanical stress, 17:20 rose senescence, 9:66 stress, 4:249-250 Abscission: anatomy and histochemistry, 1:172-203 citrus, 15:145-182, 163-166 flower and petals, 3:104-107 regulation, 7:415-416 rose, 9:63-64 Acclimatization: foliage plants, 6:119-154 herbaceous plants, 6:379-395 micropropagation, 9:278-281, 316-317 Actinidia, 6:4-12 Adzuki bean, genetics, 2: 373 Agaricus, 6:85-118 Agrobacterium tumefaciens, 3:34 Air pollution, 8:1-42 Almond: bloom delay, 15:100-101 in vitro culture, 9: 313 postharvest technology and utilization, 20:267-311 Alocasia, 8:46, 57. See also Aroids Alternate bearing: chemical thinning, 1:285-289

fruit crops, 4:128-173 pistachio, 3:387-388 Aluminum: deficiency and toxicity symptoms in fruits and nuts, 2:154 Ericaceae, 10:195-196 Amorphophallus, 8:46, 57. See also Aroids Anatomy and morphology: apple flower and fruit, 10:273-308 apple tree, 12:265-305 asparagus, 12:71 cassava, 13:106-112 citrus, abscission, 15:147-156 embryogenesis, 1:4-21, 35-40 fig, 12:420-424 fruit abscission, 1:172-203 fruit storage, 1:314 ginseng, 9:198-201 grape flower, 13:315-337 grape seedlessness, 11:160-164 heliconia, 14:5-13 kiwifruit, 6:13-50 magnetic resonance imaging, 20:78-86, 225-266 navel orange, 8:132-133 orchid,5:281-283 pecan flower, 8:217-255 petal senescence, 1:212-216 pollution injury, 8:15 Androgenesis, woody species, 10:171-173 Angiosperms, embryogenesis, 1:1-78 Anthurium, see Aroids, ornamental fertilization, 5:334-335 253

CUMULATIVE SUBJECT INDEX

254

Antitranspirants, 7:334 cold hardiness, 11:65 Apical meristem, cryopreservation, 6:357-372 Apple: alternate bearing, 4:136-137 anatomy and morphology of flower and fruit, 10:273-309 bioregulation, 10:309-401 bitter pit, 11:289-355 bloom delay, 15:102-104 CA storage, 1:303-306 chemical thinning, 1:270-300 fertilization, 1:105 fire blight control, 1:423-474 flavor, 16:197-234 flower induction, 4:174-203 fruit cracking and splitting, 19:217-262 fruiting, 11:229-287 in vitro, 5:241-243; 9:319-321 light, 2:240-248 maturity indices, 13:407-432 mealiness, 20:200 nitrogen metabolism, 4:204-246 replant disease, 2:3 root distribution, 2:453-456 stock-scion relationships, 3:315-375 summer pruning, 9:351-375 tree morphology and anatomy, 12:265-305 vegetative growth, 11:229-287 watercore, 6:189-251 yield, 1:397-424 Apricot: bloom delay, 15:101-102 CA storage, 1:309 Aroids: edible, 8:43-99; 12:166-170 ornamental,10:1-33 Arsenic, deficiency and toxicity symptoms in fruits and nuts, 2:154 Artemisia, 19:319-371

Artemisinin, 19:346-359 Artichoke, CA storage, 1:349-350 Asexual embryogenesis, 1:1-78; 2:268-310; 3:214-314; 7:163-168,171-173,176-177, 184, 185-187, 187-188, 189; 10:153-181; 14:258-259, 337-339 Asparagus: CA storage, 1:350-351 fluid drilling of seed, 3:21 postharvest biology, 12:69-155 Auxin: abscission, citrus, 15:161, 168-176 bloom delay, 15:114-115 citrus abscission, 15:161, 168-176 dormancy, 7:273-274 flowering, 15:290-291, 315 genetic regulation 16:5-6, 14, 21-22 geotropism, 15:246-267 mechanical stress, 17:18-19 petal senescence, 11:31 Avocado: flowering, 8:257-289 fruit development, 10:230-238 fruit ripening, 10:238-259 rootstocks, 17:381-429 Azalea, fertilization, 5:335-337 B

Babaco, in vitro culture, 7:178 Bacteria: diseases of fig, 12:447-451 ice nucleating, 7:210-212; 11:69-71 pathogens of bean, 3:28-58 tree short life, 2:46-47 wilt of bean, 3:46-47 Bacteriocides, fire blight, 1:450-459 Bacteriophage, fire blight control, 1:449-450

255


Banana: CA storage, 1:311-312 fertilization, 1:105 in vitro culture, 7:178-180 Bean: CA storage, 1:352-353 fluid drilling of seed, 3:21 resistance to bacterial pathogens,

Breeding, see Genetics and breeding Broccoli, CA storage, 1:354-355 Brussels sprouts, CA storage, 1:355 Bulb crops, see Tulip genetics and breeding, 18:119-123

in vitro, 18:87-169 micropropagation, 18:89-113 root physiology, 14:57-88 virus elimination, 18:113-123

3:28-58

Bedding plants, fertilization, 1:99-100; 5:337-341

Beet: CA storage, 1:353 fluid drilling of seed, 3:18-19 Begonia (Rieger), fertilization, 1:104 Biochemistry, petal senescence, 11:15-43

Biennial bearing, see Alternate bearing Bioregulation, see Growth substances apple and pear, 10:309-401 Bird damage, 6:277-278 Bitter pit in apple, 11:289-355 Blackberry harvesting, 16:282-298 Black currant, bloom delay, 15:104 Bloom delay, deciduous fruits, 15:97

Blueberry: developmental physiology, 13:339-405

harvesting, 16:257-282 nutrition, 10:183-227 Boron: deficiency and toxicity symptoms in fruits and nuts, 2:151-152 foliar application, 6:328 nutrition, 5:327-328 pine bark media, 9:119-122 Botanic gardens, 15:1-62 Bramble, harvesting, 16:282-298 Branching, lateral: apple, 10:328-330 pear, 10:328-330 Brassicaceae, in vitro, 5:232-235

c CA storage, see Controlledatmosphere (CA) storage Cabbage: CA storage, 1:355-359 fertilization, 1:117-118 Cactus: crops, 18:291-320 reproductive biology, 18:321-346 Caladium, see Aroids, ornamental Calcifuge, nutrition, 10:183-227 Calciole, nutrition, 10:183-227 Calcium: bitter pit, 11:289-355 cell wall, 5:203-205 container growing, 9:84-85 deficiency and toxicity symptoms in fruits and nuts, 2:148-149 Ericaceae nutrition, 10:196-197 foliar application, 6:328-329 fruit softening, 10:107-152 nutrition, 5:322-323 pine bark media, 9:116-117 tipburn, disorder, 4:50-57 Calmodulin, 10:132-134, 137-138 Carbohydrate: fig, 12:436-437 kiwifruit partitioning, 12:318-324 metabolism, 7:69-108 partitioning, 7:69-108 petal senescence, 11:19-20 reserves in deciduous fruit trees, 10:403-430

256

Carbon dioxide, enrichment, 7:345-398, 544-545 Carnation, fertilization, 1:100; 5:341-345 Carrot: CA storage, 1:362-366 fluid drilling of seed, 3:13-14 Caryophyllaceae, in vitro, 5:237-239 Cassava, 12:158-166; 13:105-129 Cauliflower, CA storage, 1:359-362 Celeriac, CA storage, 1:366-367 Celery: CA storage, 1:366-367 fluid drilling of seed, 3:14 Cell culture, 3:214-314 woody legumes, 14:265-332 Cell membrane: calcium, 10:126-140 petal senescence, 11:20-26 Cellular mechanisms, salt tolerance, 16:33-69 Cell wall: calcium, 10:109-122 hydrolases , 5:169-219 ice spread, 13:245-246 tomato, 13:70-71 Chelates, 9:169-171 Cherry: bloom delay, 15:105 CA storage, 1:308 origin, 19:263-317 Chestnut: blight, 8:281-336 in vitro culture, 9:311-312 Chicory, CA storage, 1:379 Chilling: injury, 4:260-261, 15:63-95 pistachio, 3:388-389 Chlorine: deficiency and toxicity symptoms in fruits and nuts, 2:153 nutrition, 5:239 Chlorosis, iron deficiency induced, 9:133-186


Chrysanthemum fertilization, 1:100-101; 5:345-352 Citrus: abscission, 15:145-182 alternate bearing, 4:141-144 asexual embryogenesis, 7:163-168 CA storage, 1:312-313 chlorosis, 9:166-168 cold hardiness, 7:201-238 fertilization, 1:105 flowering,12:349-408 honey bee pollination, 9:247-248 in vitro culture, 7:161-170 juice loss, 20:200-201 navel orange, 8:129-179 nitrogen metabolism, 8:181 rootstock,1:237-269 Cloche (tunnel), 7:356-357 Coconut palm: asexual embryogenesis, 7:184 in vitro culture, 7:183-185 Cold hardiness, 2:33-34 apple and pear bioregulation, 10:374-375 citrus, 7:201-238 factors affecting, 11:55-56 herbaceous plants, 6:373-417 injury, 2:26-27 nutrition, 3:144-171 pruning, 8:356-357 Colocasia, 8:45, 55-56. See also Aroids Common blight of bean, 3:45-46 Compositae, in vitro, 5:235-237 Container production, nursery crops, 9:75-101 Controlled environment agriculture, 7:534-545. See also

Greenhouse and greenhouse crops; Hydroponic culture; Protected crops Controlled-atmosphere (CA) storage: asparagus, 12:76-77, 127-130

257


chilling injury, 15:74-77 flowers, 3:98, 10:52-55 fruit quality, 8:101-127 fruits, 1:301-336; 4:259-260 pathogens, 3:412-461 seeds, 2:134-135 tulip, 5:105 vegetable quality, 8:101-127 vegetables, 1:337-394; 4:259-260 Copper: deficiency and toxicity symptoms in fruits and nuts, 2:153 foliar application, 6:329-330 nutrition, 5:326-327 pine bark media, 9:122-123

Corynebacterium flaccumfaciens, 3:33,46 Cowpea: genetics, 2:317-348 U.S. production, 12:197-222 Cranberry: botany and horticulture, 21:215-249 fertilization, 1:106 harvesting, 16:298-311 Cryphonectria parasitica, see

Endothia parasitica Cryopreservation: apical meristems, 6:357-372 cold hardiness, 11:65-66 Crytosperma, 8:47, 58. See also Aroids Cucumber, CA storage, 1:367-368 Currant, harvesting, 16:311-327 Cytokinin: cold hardiness, 11 :65 dormancy, 7:272-273 floral promoter, 4:112-113 flowering, 15:294-295, 318 genetic regulation, 16:4-5, 14, 22-23 grape root, 5:150, 153-156 lettuce tipburn, 4:57-58 petal senescence, 11:30-31 rose senescence, 9:66

D Date palm: asexual embryogenesis, 7:185-187 in vitro culture, 7:185-187 Daylength, see Photoperiod Dedication: Bailey, L.H., l:v-viii Beach, S.A., l:v-viii Bukovac, M.J., 6:x-xii Campbell, C.W., 19:xiii Cummins, J.N., 15:xii-xv Faust, Miklos, 5:vi-x Hackett, W.P., 12:x-xiii Halevy, A.H., 8:x-xii Hess, C.K, 13:x-xii Kader, A.A., 16:xii-xv Looney, N.K, 18:xiii Magness, J.R, 2:vi-viii Moore, J.N., 14:xii-xv Pratt, c., 20:ix Proebsting, Jr., KL., 9:x-xiv Rick, Jr., C.M., 4:vi-ix Sansavini, S., 17:xii-xiv Sherman, W.B., 21:xi-xiii Smock, RM., 7:x-xiii Weiser, c.J., 11:x-xiii Whitaker, T.W., 3:vi-x Wittwer, S.H., 10:x-xiii Deficit irrigation, 21:105-131 Deficiency symptoms, in fruit and nut crops, 2:145-154 Defoliation, apple and pear bioregulation, 10:326-328 'Delicious' apple, 1:397-424 Desiccation tolerance, 18:171-213 Dieffenbachia, see Aroids, ornamental Dioscorea, see Yam Disease: and air pollution, 8:25 aroids, 8:67-69; 10:18; 12:168-169 bacterial, of bean, 3:28-58 cassava, 12:163-164


258

Disease (cont'd) controlled-atmosphere storage,

controlled for agriculture, 7:534-545

controlled for energy efficiency,

3:412-461

control by virus, 3:399-403 cowpea, 12:210-213 fig, 12:447-479 flooding, 13:288-299 hydroponic crops, 7:530-534 lettuce, 2:187-197 mycorrhizal fungi, 3:182-185 ornamental aroids, 10:18 resistance, acquired, 18:247-289 root, 5:29-31 stress, 4:261-262 sweet potato, 12:173-175 tulip, 5:63, 92 turnip moasic virus, 14:199-238 yam (Dioscorea), 12:181-183 Disorder, see Postharvest physiology bitterpit, 11:289-355 fig, 12:477-479 pear fruit, 11:357-411 watercore, 6:189-251; 11:385-387 Dormancy, 2:27-30 blueberry, 13:362-370 release in fruit trees, 7:239-300 tulip, 5:93 Drip irrigation, 4:1-48 Drought resistance, 4:250-251 cassava, 13:114-115 Dwarfing: apple, 3:315-375 apple mutants, 12:297-298 by virus, 3:404-405

1:141-171,9:1-52

embryogenesis, 1:22,43-44 fruit set, 1:411-412 ginseng, 9:211-226 greenhouse management, 9:32-38 navel orange, 8:138-140 nutrient film technique, 5:13-26 Epipremnum, see Aroids, ornamental Erwinia: amylovora, 1:423-474 lathyri, 3:34 Essential elements: foliar nutrition, 6:287-355 pine bark media, 9:103-131 plant nutrition 5:318-330 soil testing, 7:1-68 Ethylene: abscission, citrus, 15:158-161, 168-176

apple bioregulation, 10:366-369 avocado, 10:239-241 bloom delay, 15:107-111 CA storage, 1:317-319, 348 chilling injury, 15:80 citrus abscission, 15:158-161, 168-176

cut flower storage, 10:44-46 dormancy, 7:277-279 flowering, 15:295-296,319 flower longevity, 3:66-75 genetic regulation, 16:6-7, 14-15, 19-20

kiwifruit respiration, 6:47-48 mechanical stress, 17:16-17 petal senescence, 11:16-19, 27-30 rose senescence, 9:65-66

E Easter lily, fertilization, 5:352-355 Embryogenesis, see Asexual embryogenesis Endothia parasitica, 8:291-336 Energy efficiency, in greenhouses, 1:141-171; 9:1-52

Environment: air pollution, 8:20-22

F Feed crops, cactus, 18:298-300 Fertilization and fertilizer: anthurium, 5:334-335


azalea, 5:335-337 bedding plants, 5:337-341 blueberry, 10:183-227 carnation, 5:341-345 chrysanthemum, 5:345-352 controlled release, 1:79-139; 5:347-348 Easter lily, 5:352-355 Ericaceae, 10:183-227 foliage plants, 5:367-380 foliar, 6:287-355 geranium, 5:355-357 greenhouse crops, 5:317-403 lettuce, 2:175 nitrogen, 2:401-404 orchid,5:357-358 poinsettia, 5:358-360 rose, 5:361-363 snapdragon, 5:363-364 soil testing, 7:1-68 trickle irrigation, 4:28-31 tulip, 5:364-366 Vaccinium, 10:183-227 Fig: industry, 12:409-490 ripening, 4:258-259 Filbert, in vitro culture, 9:313-314 Fire blight, 1:423-474 Flooding, fruit crops, 13:257-313 Floricultural crops, see individual

crops fertilization, 1:98-104 growth regulation, 7:399-481 heliconia, 14:1-55 postharvest physiology and senescence, 1:204-236; 3:59-143; 10:35-62; 11:15-43 Florigen, 4:94-98 Flower and flowering: alternate bearing, 4:149 apple anatomy and morphology, 10:277-283 apple bioregulation, 10:344-348 aroids, ornamental, 10:19-24 avocado, 8:257-289

259

blueberry development, 13:354-378 cactus, 18:325-335 citrus, 12:349-408 control, 4:159-160, 15:279-334 development (postpollination), 19:1-58 fig, 12:424-429 grape anatomy and morphology, 13:354-378 honey bee pollination, 9:239-243 induction, 4:174-203; 254-256 initiation, 4:152-153 in vitro, 4:106-127 kiwifruit, 6:21-35; 12:316-318 orchid, 5:297-300 pear bioregulation, 10:344-348 pecan, 8:217-255 perennial fruit crops, 12:223-264 phase change, 7:109-155 photoperiod, 4:66-105 pistachio, 3:378-387 postharvest physiology, 1:204-236; 3:59-143; 10:35-62; 11:15-43 postpollination development, 19:1-58 pratea leaf blackening, 17:173-201 pruning, 8:359-362 raspberry, 11:187-188 regulation in floriculture, 7:416-424 rhododendron, 12:1-42 rose, 9:60-66 senescence, 1:204-236; 3:59-143; 10:35-62; 11:15-43; 18:1-85 sugars, 4:114 thin cell layer morphogenesis, 14:239-256 tulip, 5:57-59 water relations, 18:1-85 Fluid drilling, 3:1-58 Foliage plants: acclimatization, 6:119-154 fertilization, 1:102-103; 5:367-380


260

Foliar nutrition, 6:287-355 Freeze protection, see Frost protection Frost: apple fruit set, 1:407-408 citrus, 7:201-238 protection, 11 :45-109 Fruit: abscission, 1:172-203 citrus, 15:145-182 apple anatomy and morphology, 10:283-297

apple bioregulation, 10:348-374 apple bitter pit, 11 :289-355 apple flavor, 16:197-234 apple maturity indices, 13:407-432

apple ripening and quality, 10:361-374

avocado development and ripening, 10:229-271 bloom delay, 15:97-144 blueberry development, 13:378-390

cactus physiology, 18:335-341 CA storage and quality, 8:101-127 chilling injury, 15:63-95 cracking, 19:217-262 diseases in CA storage, 3:412-461 drop, apple and pear, 10:359-361 fig, 12:424-429 kiwifruit, 6:35-48; 12:316-318 maturity indices, 13:407-432 navel orange, 8:129-179 nectarine, postharvest, 11:413-452 nondestructive postharvest quality evaluation, 20:1-119 peach, postharvest, 11:413-452 pear: bioregulation, 10:348-374 fruit disorders, 11: 35 7-411 pear maturity indices, 13:407-432 pear ripening and quality, 10:361-374

pistachio, 3:382-391 quality and pruning, 8:365-367

ripening, 5:190-205 set, 1:397-424; 4:153-154 set in navel oranges, 8:140-142 size and thinning, 1:293-294; 4:161

softening, 5:109-219, 10:107-152 splitting, 19:217-262 strawberry growth and ripening, 17:267-297

texture, 20:121-224 thinning, apple and pear, 10:353-359

tomato parthenocarpy, 6:65-84 tomato ripening, 13:67-103 Fruit crops: alternate bearing, 4:128-173 apple bitter pit, 11:289-355 apple flavor, 16:197-234 apple fruit splitting and cracking, 19:217-262

apple growth, 11:229-287 apple maturity indices, 13:407-432

avocado flowering, 8:257-289 avocado rootstocks, 17:381-429 berry crop harvesting, 16:255-382 bloom delay, 15:97-144 blueberry developmental physiology, 13:339-405 blueberry harvesting, 16:257-282 blueberry nutrition, 10:183-227 bramble harvesting, 16:282-298 cactus, 18:302-309 carbohydrate reserves, 10:403-430 CA storage, 1:301-336 CA storage diseases, 3:412-461 cherry origin, 19:263-317 chilling injury, 15:145-182 chlorosis, 9:161-165 citrus abscission, 15:145-182 citrus cold hardiness, 7:201-238 citrus flowering, 12:349-408 cranberry, 21:215-249 cranberry harvesting, 16:298-311 currant harvesting, 16:311-327 deficit irrigation, 21:105-131


dormancy release, 7:239-300 Ericaceae nutrition, 10:183-227 fertilization, 1:104-106 fig, industry, 12:409-490 fireblight, 11:423-474 flowering, 12:223-264 foliar nutrition, 6:287-355 frost control, 11:45-109 grape flower anatomy and morphology, 13:315-337 grape harvesting, 16:327-348 grape nitrogen metabolism, 14:407-452

grape pruning, 16:235-254, 336-340

grape root, 5:127-168 grape seedlessness, 11:164-176 grapevine pruning, 16:235-254,

261

Phytophthora control, 17:299-330 pruning, 8:339-380 rambutan, 16:143-196 raspberry, 11:185-228 roots, 2:453-457 sapindaceous fruits, 16:143-196

short life and replant problem, 2:1-116

strawberry fruit growth, 17:267-297

strawberry harvesting, 16:348-365 summer pruning, 9:351-375 Vaccinium nutrition, 10:183-227 water status, 7:301-344 Fungi: fig, 12:451-474 mushroom, 6:85-118 mycorrhiza, 3:172-213; 10:211-212

336-340

honey bee pollination, 9:244-250,

pathogens in postharvest storage,

254-256

in vitro culture, 7:157-200; 9:273-349

irrigation, deficit, 21:105-131 jojoba, 17:233-266 kiwifruit, 6:1-64; 12:307-347 longan, 16:143-196 lychee, 16:143-196 muscadine grape breeding, 14:357-405

navel orange, 8:129-179 nectarine postharvest, 11:413-452 nondestructive postharvest quality evaluation 20:1-119 nutritional ranges, 2:143-164 olive salinity tolerance, 21:177-214

orange, navel, 8:129-179 orchard floor management, 9:377-430

peach origin, 17:331-379 peach postharvest, 11:413-452 pear fruit disorders, 11:357-411 pear maturity indices, 13:407-432 pecan flowering, 8:217-255 photosynthesis, 11:111-157

3:412-461

truffle cultivation, 16:71-107 Fungicide, and apple fruit set, 1:416

G

Garlic, CA storage, 1:375 Genetics and breeding: aroids (edible), 8:72-75; 12:169 aroids (ornamental), 10:18-25 bean, bacterial resistance, 3:28-58 bloom delay in fruits, 15:98-107 bulbs, flowering, 18:119-123 cassava, 12:164 chestnut blight resistance, 8:313-321

citrus cold hardiness, 7:221-223 cranberry, 21:236-239 embryogenesis, 1:23 fig, 12:432-433 fire blight resistance, 1:435-436 flowering, 15:287-290, 303-305, 306-309, 314-315

flower longevity, 1 :208-209 ginseng, 9:197-198


262

Genetics and breeding (cont'd) in vitro techniques, 9:318-324; 18:119-123

lettuce, 2:185-187 muscadine grapes, 14:357-405 mushroom, 6:100-111 navel orange, 8:150-156 nitrogen nutrition, 2:410-411 pineapple, 21:138-164 plant regeneration, 3:278-283 pollution insensitivity, 8:18-19 potato tuberization, 14:121-124 rhododendron, 12:54-59 sweet potato, 12:175 sweet sorghum, 21:87-90 tomato parthenocarpy, 6:69-70 tomato ripening, 13:77-98 tree short life, 2:66-70 Vigna, 2:311-394 woody legume tissue and cell culture, 14:311-314 yam (Dioscorea), 12:183 Genetic variation: alternate bearing, 4:146-150 photoperiodic response, 4:82 pollution injury, 8:16-19 temperature-photoperiod interaction, 17:73-123 Geophyte, see Bulb crops Geranium, fertilization, 5:355-357 Germination, seed, 2:117-141, 173-174

Germplasm preservation: cryopreservation, 6:357-372 in vitro, 5:261-264; 9:324-325 pineapple, 21:164-168 Germplasm resources, pineapple, 21:133-175

Gibberellin: abscission, citrus, 15:166-167 bloom delay, 15:111-114 citrus, abscission, 15:166-167 cold hardiness, 11:63 dormancy, 7:270-271 floral promoter, 4:114 flowering, 15:219-293,315-318

genetic regulation, 16:15 grape root, 5:150-151 mechanical stress, 17:19-20 Ginseng, 9:187-236 Girdling, 4:251-252 Glucosinolates, 19:99-215 Graft and grafting: incompatibility, 15:183-232 phase change, 7:136-137, 141-142 rose, 9:56-57 Grape: CA storage, 1:308 chlorosis, 9:165-166 flower anatomy and morphology, 13:315-337

harvesting, 16:327-348 muscadine breeding, 14:357-405 nitrogen metabolism, 14:407-452 pollen morphology, 13:331-332 pruning, 16:235-254, 336-340 root, 5:127-168 seedlessness, 11:159-187 sex determination, 13:329-331 Gravitropism, 15:233-278 Greenhouse and greenhouse crops: carbon dioxide, 7:357-360, 544-545

energy efficiency, 1:141-171; 9:1-52

growth substances, 7:399-481 nutrition and fertilization, 5:317-403

pest management, 13:1-66 vegetables, 21:1-39 Growth regulators, see Growth substances Growth substances, 2:60-66. See also Abscisic acid; Auxin; Cytokinin; Ethylene; Gibberellin abscission, citrus, 15:157-176 apple bioregulation, 10:309-401 apple dwarfing, 3:315-375 apple fruit set, 1:417 apple thinning, 1:270-300 aroids, ornamental, 10:14-18


avocado fruit development, 10:229-243 bloom delay, 15:107-119

CA storage in vegetables,

263

Heliconia, 14:1-55 Herbaceous plants, subzero stress, 6:373-417

Herbicide-resistant crops,

1:346-348

cell cultures, 3:214-314 chilling injury, 15:77-83 citrus abscission, 15:157-176 cold hardiness 7:223-225; 11:58-66

dormancy, 7:270-279 embryogenesis, 1:41-43; 2:277-281

floriculture, 7:399-481 flower induction, 4:190-195 flowering, 15:290-296 flower storage, 10:46-51 genetic regulation, 16:1-32 ginseng, 9:226 grape seedlessness, 11:177-180 in vitro flowering, 4:112-115 mechanical stress, 17:16-21 meristem and shoot-tip culture, 5:221-227

navel oranges, 8:146-147 pear bioregulation, 10:309-401 petal senescence, 3:76-78 phase change, 7:137-138, 142-143

raspberry, 11:196-197 regulation, 11:1-14 rose, 9:53-73 seedlessness in grape, 11:177-180 triazole, 10:63-105 H

Halo blight of beans, 3 :44-45 Hardiness, 4:250-251 Harvest: flower stage, 1:211-212 index, 7:72-74 lettuce, 2:176-181 mechanical of berry crops, 16:255-382

Hazelnut, see Filbert, in vitro culture

15:371-412

Histochemistry: flower induction, 4:177-179 fruit abscission, 1:172-203 Histology, flower induction, 4:179-184. See also Anatomy and morphology Honey bee, 9:237-272 Horseradish, CA storage, 1:368 Hydrolases, 5:169-219 Hydroponic culture, 5:1-44; 7:483-558

Hypovirulence, in Endothia parasitica, 8:299-310 I

Ice, formation and spread in tissues, 13:215-255

Ice-nucleating bacteria, 7:210-212; 13:230-235

Industrial crops, cactus, 18:309-312 Insects and mites: aroids, 8:65-66 avocado pollination, 8:275-277 fig, 12:442-447 hydroponic crops, 7:530-534 integrated pest management, 13:1-66

lettuce, 2:197-198 ornamental aroids, 10:18 tree short life, 2: 5 2 tulip, 5:63,92 Integrated pest management, greenhouse crops, 13:1-66 In vitro: abscission, 15:156-157 apple propagation, 10:325-326 aroids, ornamental, 10:13-14 artemisia, 19:342-345 bulbs, flowering, 18:87-169 cassava propagation, 13:121-123

264 In vitro (cont'd) cellular salinity tolerance, 16:33-69 cold acclimation, 6:382 cryopreservation, 6:357-372 embryogenesis, 1:1-78; 2:268-310; 7:157-200; 10:153-181 environmental control, 17:123-170 flowering, 4:106-127 flowering bulbs, 18:87-169 pear propagation, 10:325-326 phase change, 7:144-145 propagation, 3:214-314; 5:221-277; 7:157-200; 9:57-58,273-349; 17:125-172 thin cell layer morphogenesis, 14:239-264 woody legume culture, 14:265-332 Iron: deficiency chlorosis, 9:133-186 deficiency and toxicity symptoms in fruits and nuts, 2:150 Ericaceae nutrition, 10:193-195 foliar application, 6:330 nutrition, 5:324-325 pine bark media, 9:123 Irrigation: deficit, deciduous orchards, 21:105-131 drip or trickle, 4:1-48 frost control, 11: 76-82 fruit trees, 7:331-332 grape root growth, 5:140-141 lettuce industry, 2:175 navel orange, 8:161-162 root growth, 2:464-465

J Jojoba, 17:233-266 Juvenility, 4:111-112 pecan, 8:245-247 tulip, 5:62-63 woody plants, 7:109-155


K

Kale, fluid drilling of seed, 3:21 Kiwifruit: botany, 6:1-64 vine growth, 12:307-347 L

Lamps, for plant growth, 2:514-531 Leaves: apple morphology, 12:283-288 flower induction, 4:188-189 Leek: CA storage, 1:375 fertilization, 1:118 Leguminosae, in vitro, 5:227-229; 14:265-332 Lemon, rootstock, 1:244-246. See also Citrus Lettuce: CA storage, 1:369-371 fertilization, 1:118 fluid drilling of seed, 3:14-17 industry, 2:164-207 tipburn, 4:49-65 Light: fertilization, greenhouse crops, 5:330-331 flowering, 15:282-287, 310-312 fruit set, 1:412-413 lamps, 2:514-531 nitrogen nutrition, 2:406-407 orchards, 2:208-267 ornamental aroids, 10:4-6 photoperiod,4:66-105 photosynthesis, 11:117-121 plant growth, 2:491-537 tolerance, 18:215-246 Longan, see Sapindaceous fruits Lychee, see Sapindaceous fruits

M Magnesium: container growing, 9:84-85


deficiency and toxicity symptoms in fruits and nuts, 2:148 Ericaceae nutrition, 10:196-198 foliar application, 6:331 nutrition, 5:323 pine bark media, 9:117-119 Magnetic resonance imaging, 20:78-86, 225-266 Male sterility, temperaturephotoperiod induction, 17:103-106 Mandarin, rootstock, 1:250-252 Manganese: deficiency and toxicity symptoms in fruits and nuts, 2:150-151 Ericaceae nutrition, 10:189-193 foliar application, 6:331 nutrition, 5:235-326 pine bark media, 9:123-124 Mango: alternate bearing, 4:145-146 asexual embryogenesis, 7:171-173 CA storage, 1:313 in vitro culture, 7:171-173 Mechanical harvest, berry crops, 16:255-382 Mechanical stress regulation, 17:1-42 Media: fertilization, greenhouse crops, 5:333 pine bark, 9:103-131 Medicinal crops: artemisia, 19:319-371 poppy, 19:373-408 Meristem culture, 5:221-277 Metabolism: flower, 1:219-223 nitrogen in citrus, 8:181-215 seed,2:117-141 Micronutrients: container growing, 9:85-87 pine bark media, 9:119-124 Micropropagation, see In vitro; Propagation bulbs, flowering, 18:89-113

265

environmental control, 17:125-172 nuts, 9:273-349 rose, 9:57-58 temperate fruits, 9:273-349 tropical fruits and palms, 7:157-200 Microtus, see Vole Moisture, and seed storage, 2:125-132 Molybdenum nutrition, 5:328-329 Monocot, in vitro, 5:253-257 Monstera, see Aroids, ornamental Morphology: navel orange, 8:132-133 orchid, 5:283-286 pecan flowering, 8:217-243 Moth bean, genetics, 2:373-374 Mung bean, genetics, 2:348-364 Mushroom: CA storage, 1:371-372 cultivation, 19:59-97 spawn, 6:85-118 Muskmelon, fertilization, 1:118-119 Mycoplasma-like organisms, tree short life, 2:50-51 Mycorrhizae: container growing, 9:93 Ericaceae, 10:211-212 fungi, 3:172-213 grape root, 5:145-146 N

Navel orange, 8:129-179 Nectarine: bloom delay, 15:105-106 CA storage, 1:309-310 postharvest physiology, 11:413-452 Nematodes: aroids, 8:66 fig, 12:475-477 lettuce, 2:197-198 tree short life, 2:49-50


266

NFT (nutrient film technique), 5:1-44 Nitrogen: CA storage, 8:116-117 container growing, 9:80-82 deficiency and toxicity symptoms in fruits and nuts, 2:146 in embryogenesis, 2:273-275 Ericaceae nutrition, 10:198-202 fixation in woody legumes, 14:322-323 foliar application, 6:332 metabolism in apple, 4:204-246 metabolism in citrus, 8:181-215 metabolism in grapevine, 14:407-452 nutrition, 2:395,423; 5:319-320 pine bark media, 9:108-112 trickle irrigation, 4:29-30 Nondestructive quality evaluation of fruits and vegetabl'es, 20:1-119 Nursery crops: fertilization, 1:106-112 nutrition, 9:75-101 Nut crops: almond postharvest technology and utilization, 20:267-311 chestnut blight, 8:291-336 fertilization, 1:106 honey bee pollination, 9:250-251 in vitro culture, 9:273-349 nutritional ranges, 2:143-164 pistachio culture, 3:376-396 Nutrient: concentration in fruit and nut crops, 2:154-162 film technique, 5:1-44 foliar-applied,6:287-355 media, for asexual embryogenesis, 2:273-281 media, for organogenesis, 3:214-314 plant and tissue analysis, 7:30-56 solutions, 7:524-530

uptake, in trickle irrigation, 4:30-31 Nutrition (human): aroids, 8:79-84 CA storage, 8:101-127 Nutrition (plant): air pollution, 8:22-23, 26 blueberry, 10:183-227 calcifuge, 10:183-227 cold hardiness, 3:144-171 container nursery crops, 9:75-101 cranberry, 21:234-235 embryogenesis, 1:40-41 Ericaceae, 10:183-227 fire blight, 1:438-441 foliar, 6:287-355 fruit and nut crops, 2:143-164 ginseng, 9:209-211 greenhouse crops, 5:317-403 kiwifruit, 12:325-332 mycorrhizal fungi, 3:185-191 navel orange, 8:162-166 nitrogen in apple, 4:204-246 nutrient film techniques, 5:18-21, 31-53 ornamental aroids, 10:7-14 pine bark media, 9:103-131 raspberry, 11:194-195 slow-release fertilizers, 1:79-139

o Oil palm: asexual embryogenesis, 7:187-188 in vitro culture, 7:187-188 Okra: botany and horticulture, 21:41-72 CA storage, 1:372-373 Olive: alternate bearing, 4:140-141 salinity tolerance, 21:177-214 Onion: CA storage, 1:373-375 fluid drilling of seed, 3:17-18 Opium poppy, 19:373-408


Orange, see Citrus alternate bearing, 4:143-144 sour, rootstock, 1:242-244 sweet, rootstock, 1:252-253 trifoliate, rootstock, 1:247-250 Orchard and orchard systems: floor management, 9:377-430 light, 2:208-267 root growth, 2:469-470 water, 7:301-344 Orchid: fertilization, 5:357-358 physiology, 5:279-315 pollination regulation of flower development, 19:28-38 Organogenesis, 3:214-314. See also In vitro; Tissue, culture Ornamental plants: chlorosis, 9:168-169 fertilization, 1:98-104, 106-116 flowering bulb roots, 14:57-88 flowering bulbs in vitro, 18:87-169

foliage acclimatization, 6: 119-154 heliconia, 14:1-55 orchid pollination regulation, 19:28-38

poppy, 19:373-408 protea leaf blackening, 17:173-201

rhododendron, 12:1-42 p

Paclobutrazol, see Triazole Papaya: asexual embryogenesis, 7:176-177 CA storage, 1:314 in vitro culture, 7:175-178 Parsley: CA storage, 1:375 drilling of seed, 3:13-14 Parsnip, fluid drilling of seed, 3:13-14

Parthenocarpy, tomato, 6:65-84

267

Passion fruit, in vitro culture, 7:180-181

Pathogen elimination, in vitro, 5:257-261

Peach: bloom delay, 15:105-106 CA storage, 1:309-310 origin, 17:333-379 postharvest physiology, 11:413-452

short life, 2:4 summer pruning, 9:351-375 wooliness, 20:198-199 Peach palm (Pejibaye), in vitro culture, 7:187-188 Pear: bioregulation, 10:309-401 bloom delay, 15:106-107 CA storage, 1:306-308 decline, 2:11 fire blight control, 1:423-474 fruit disorders, 11: 35 7-411 in vitro, 9:321 maturity indices, 13:407-432 root distribution, 2:456 short life, 2:6 Pecan: alternate bearing, 4:139-140 fertilization, 1: 1 06 flowering, 8:217-255 in vitro culture, 9:314-315 Pejibaye, in vitro culture, 7:189 Pepper (Capsicum): CA storage, 1:375-376 fertilization, 1:119 fluid drilling in seed, 3:20 Persimmon: CA storage, 1:314 quality, 4:259 Pest control: aroids (edible), 12:168-169 aroids (ornamental), 10:18 cassava, 12:163-164 cowpea, 12:210-213 fig, 12:442-477


268

Pest control (cont'd) fire blight, 1:423-474 ginseng, 9:227-229 greenhouse management, 13:1-66 hydroponics, 7:530-534 sweet potato, 12:173-175 vertebrate, 6:253-285 yam (Dioscorea), 12:181-183 Petal senescence, 11:15-43 pH: container growing, 9:87-88 fertilization greenhouse crops, 5:332-333

pine bark media, 9:114-117 soil testing, 7:8-12, 19-23 Phase change, 7:109-155 Phenology: apple, 11:231-237 raspberry, 11:186-190 Philodendron, see Aroids, ornamental Phosphonates, Phytophthora control, 17:299-330 Phosphorus: container growing, 9:82-84 deficiency and toxicity symptoms in fruits and nuts, 2:146-147 nutrition, 5:320-321 pine bark media, 9:112-113 trickle irrigation, 4:30 Photoautotrophic micropropagation, 17:125-172

Photoperiod, 4:66-105,116-117; 17:73-123

flowering, 15:282-284, 310-312 Photosynthesis: cassava, 13:112-114 efficiency, 7:71-72; 10:378 fruit crops, 11:111-157 ginseng, 9:223-226 light, 2:237-238 Physiology, see Postharvest physiology bitter pit, 11 :289-355 blueberry development, 13:339-405

cactus reproductive biology, 18:321-346

calcium, 10:107-152 carbohydrate metabolism, 7:69-108

cassava, 13:105-129 citrus cold hardiness, 7:201-238 conditioning 13:131-181 cut flower, 1:204-236; 3:59-143; 10:35-62

desiccation tolerance, 18:171-213 disease resistance, 18:247-289 dormancy, 7:239-300 embryogenesis, 1:21-23; 2:268-310

flower development, 19:1-58 flowering, 4:106-127 fruit ripening, 13:67-103 fruit softening, 10:107-152 ginseng, 9:211-213 glucosinolates, 19:99-215 heliconia, 14:5-13 juvenility, 7:109-155 light tolerance, 18:215-246 male sterility, 17:103-106 mechanical stress, 17:1-42 nitrogen metabolism in grapevine, 14:407-452

nutritional quality and CA storage, 8:118-120

olive salinity tolerance, 21:177-214

orchid, 5:279-315 petal senescence, 11:15-43 photoperiodism, 17:73-123 pollution injury, 8:12-16 polyamines, 14:333-356 potato tuberization, 14:89-188 pruning, 8:339-380 raspberry, 11:190-199 regulation, 11:1-14 root pruning, 6:158-171 roots of flowering bulbs, 14:57-88 rose, 9:3-53 salinity hormone action, 16:1-32 salinity tolerance, 16:33-69


seed,2:117-141 seed priming, 16:109-141 subzero stress, 6:373-417 summer pruning, 9:351-375 thin cell layer morphogenesis, 14:239-264 tomato fruit ripening, 13:67-103 tomato parthenocarpy, 6:71-74 triazole, 10:63-105 tulip, 5:45-125 vernalization, 17:73-123 volatiles, 17:43-72 watercore, 6:189-251 water relations cut flowers, 18:1-85 Phytohormones, see Growth substances Phytophthora control, 17:299-330 Phytotoxins, 2:53-56 Pigmentation: flower, 1:216-219 rose, 9:64-65 Pinching, by chemicals, 7:453-461 Pineapple: CA storage, 1:314 genetic resources, 21:138-141 in vitro culture, 7:181-182 Pine bark, potting media, 9:103-131 Pistachio: alternate bearing, 4:137-139 culture, 3:376-393 in vitro culture, 9: 315 Plantain, in vitro culture, 7:178-180 Plant protection, short life, 2:79-84 Plum, CA storage, 1:309 Poinsettia, fertilization, 1:103-104; 5:358-360 Pollen, desiccation tolerance, 18:195 Pollination: apple, 1:402-404 avocado, 8:272-283 cactus, 18:331-335 embryogenesis, 1:21-22 fig, 12:426-429 flower regulation, 19:1-58 fruit crops, 12:223-264 fruit set, 4:153-154

269

ginseng, 9:201-202 grape, 13:331-332 heliconia, 14:13-15 honey bee, 9:237-272 kiwifruit, 6:32-35 navel orange, 8:145-146 orchid, 5:300-302 petal senescence, 11:33-35 protection, 7:463-464 rhododendron, 12:1-67 Pollution, 8:1-42 Polyamines, 14:333-356 chilling injury, 15:80 Polygalacturonase, 13:67-103 Postharvest physiology: almond, 20:267-311 apple bitter pit, 11:289-355 apple maturity indices, 13:407-432 aroids, 8:84-86 asparagus, 12:69-155 CA storage and quality, 8:101-127 cut flower, 1:204-236; 3:59-143; 10:35-62 foliage plants, 6:119-154 fruit, 1:301-336 fruit softening, 10:107-152 lettuce, 2:181-185 low-temperature sweetening, 17:203-231 navel orange, 8:166-172 nectarine, 11:413-452 nondestructive quality evaluation, 20:1-119 pathogens, 3:412-461 peach,11:413-452 pear disorders, 11:357-411 pear maturity indices, 13:407-432 petal senescence, 11:15-43 pratea leaf blackening, 17:173-201 quality evaluation, 20:1-119 seed,2:117-141 texture in fresh fruit, 20:121-244 tomato fruit ripening, 13:67-103


270

Postharvest physiology (cont'd) vegetables, 1:337-394 watercore, 6:189-251; 11:385-387 Potassium: container growing, 9:84 deficiency and toxicity symptoms in fruits and nuts, 2:147-148 foliar application, 6:331-332 nutrition, 5:321-322 pine bark media, 9:113-114 trickle irrigation, 4:29 Potato: CA storage, 1:376-378 fertilization, 1:120-121 low temperature sweetening, 17:203-231 tuberization, 14:89-198 Propagation, see In vitro apple, 10:324-326; 12:288-295 aroids, ornamental, 10:12-13 cassava, 13:120-123 floricultural crops, 7:461-462 ginseng, 9:206-209 orchid,5:291-297 pear, 10:324-326 rose, 9:54-58 tropical fruit, palms 7:157-200 woody legumes in vitro, 14:265-332 Protea, leaf blackening, 17:173-201 Protected crops, carbon dioxide, 7:345-398 Protoplast culture, woody species, 10:173-201 Pruning, 4:161,8:339-380 apple, 9:351-375 apple training, 1:414 chemical, 7:453-461 cold hardiness, 11:56 fire blight, 1:441-442 grapevines, 16:235-254 light interception, 2:250-251 peach,9:351-375 phase change, 7:143-144 root, 6:155-188

Prunus, see Almond; Cherry; Nectarine; Peach; Plum, CA Storage in vitro, 5:243-244; 9:322 root distribution, 2:456 Pseudomonas: phaseolicola, 3:32-33, 39, 44-45 solanacearum, 3:33 syringae, 3:33,40; 7:210-212

Q Quality evaluation: fruits and vegetables, 20:1-119, 121-224 nondestructive, 20:1-119 texture in fresh fruit, 20:121-224 R

Rabbit, 6:275-276 Radish, fertilization, 1:121 Rambutan, see Sapindaceous fruits Raspberry: harvesting, 16:282-298 productivity, 11:185-228 Rejuvenation: rose, 9:59-60 woody plants, 7:109-155 Replant problem, deciduous fruit trees, 2:1-116 Respiration: asparagus postharvest, 12:72-77 fruit in CA storage, 1:315-316 kiwifruit, 6:47-48 vegetables in CA storage, 1:341-346 Rhizobium, 3:34,41 Rhododendron, 12:1-67 Rice bean, genetics, 2:375-376 Root: apple, 12:269-272 cactus, 18:297-298 diseases, 5:29-31


environment, nutrient film technique, 5:13-26 Ericaceae, 10:202-209 grape, 5:127-168 kiwifruit, 12:310-313 physiology of bulbs, 14:57-88 pruning, 6:155-188 raspberry, 11:190 rose, 9:57 tree crops, 2:424-490 Root and tuber crops: aroids, 8:43-99; 12:166-170 cassava, 12:158-166 low-ternperature sweetening, 17:203-231 minor crops, 12:184-188 potato tuberization, 14:89-188 sweet potato, 12:170-176 yam (Dioscorea), 12:177-184 Rootstocks: alternate bearing, 4:148 apple, 1:405-407; 12:295-297 avocado, 17:381-429 citrus, 1:237-269 cold hardiness, 11:57-58 fire blight, 1:432-435 light interception, 2:249-250 navel orange, 8:156-161 root systems, 2:471-474 stress, 4:253-254 tree short life, 2:70-75 Rosaceae, in vitro, 5:239-248 Rose: fertilization, 1:104; 5:361-363 growth substances, 9:3-53 in vitro, 5:244-248

s Salinity: air pollution, 8:25-26 olive, 21:177-214 soils, 4:22-27 tolerance, 16:33-69 Sapindaceous fruits, 16:143-196

271

Scoring, and fruit set, 1:416-417 Seed: abortion, 1:293-294 apple anatomy and morphology, 10:285-286 conditioning, 13:131-181 desiccation tolerance, 18:196-203 environmental influences on size and composition, 13:183-213 flower induction, 4:190-195 fluid drilling, 3:1-58 grape seedlessness, 11:159-184 kiwifruit, 6:48-50 lettuce, 2:166-174 priming, 16:109-141 rose propagation, 9:54-55 vegetable, 3:1-58 viability and storage, 2:117-141 Secondary metabolites, woody legumes, 14:314-322 Senescence: cut flower, 1:204-236; 3:59-143; 10:35-62; 18:1-85 petal,11:15-43 pollination-induced, 19:4-25 rose, 9:65-66 whole plant, 15:335-370 Sensory quality, CA storage, 8:101-127 Shoot-tip culture, 5:221-277. See also Micropropagation Short life problem, fruit crops, 2:1-116 Small fruit, CA storage, 1:308 Snapdragon fertilization, 5:363-364 Sodium, deficiency and toxicity symptoms in fruits and nuts, 2:153-154 Soil: grape root growth, 5:141-144 management and root growth, 2:465-469 orchard floor management, 9:377-430


272

Soil (cont'd) plant relations, trickle irrigation, 4:18-21 stress, 4:151-152 testing, 7:1-68; 9:88-90 Soilless culture, 5:1-44 Solanaceae, in vitro, 5:229-232 Somatic embryogenesis, see Asexual embryogenesis Sorghum, sweet, 21:73-104 Spathiphyllum, see Aroids, ornamental Stem, apple morphology, 12:272-283 Storage, see Postharvest physiology, Controlled-atmosphere (CA) storage cut flower, 3:96-100; 10:35-62 rose plants, 9:58-59 seed,2:117-141 Strawberry: fertilization, 1:106 fruit growth and ripening, 17:267-297 harvesting, 16:348-365 in vitro, 5:239-241 Stress: benefits of, 4:247-271 climatic, 4:150-151 flooding, 13:257-313 mechanical, 17:1-42 petal, 11:32-33 plant, 2:34-37 protection, 7:463-466 salinity tolerance in olive, 21:177-214 subzero temperature, 6:373-417 Sugar beet, fluid drilling of seed, 3:18-19 Sugar, see Carbohydrate allocation, 7:74-94 flowering, 4:114 Sulfur: deficiency and toxicity symptoms in fruits and nuts, 2:154 nutrition, 5:323-324

Sweet potato: culture, 12:170-176 fertilization, 1:121 Symptoms, deficiency and toxicity symptoms in fruits and nuts, 2:145-154 Syngonium, see Aroids, ornamental

T Taro, see Aroids, edible Temperature: apple fruit set, 1:408-411 bloom delay, 15:119-128 CA storage of vegetables, 1:340-341 chilling injury, 15:67-74 cut flower storage, 10:40-43 cryopreservation, 6:357-372 fertilization, greenhouse crops, 5:331-332 fire blight forecasting, 1:456-459 flowering, 15:284-287, 312-313 interaction with photoperiod, 4:80-81 low temperature sweetening, 17:203-231 navel orange, 8:142 nutrient film technique, 5:21-24 photoperiod interaction, 17:73-123 photosynthesis, 11:121-124 plant growth, 2:36-37 seed storage, 2:132-133 subzero stress, 6:373-417 Texture in fresh fruit, 20:121-224 Thinning, apple, 1:270-300 Tipburn, in lettuce, 4:49-65 Tissue, see In vitro culture, 1:1-78; 2:268-310; 3:214-314; 4:106-127; 5:221-277; 6:357-372; 7:157-200; 8:75-78; 9:273-349; 10:153-181


dwarfing, 3:347-348 nutrient analysis, 7:52-56; 9:90 Tomato: CA storage, 1:380-386 chilling injury, 20:199-200 fertilization, 1:121-123 fluid drilling of seed, 3:19-20 fruit ripening, 13:67-103 galacturonase, 13:67-103 parthenocarpy, 6:65-84 Toxicity symptoms in fruit and nut crops, 2:145-154 Transport, cut flowers, 3:100-104 Tree decline, 2:1-116 Triazole, 10:63-105 chilling injury, 15:79-80 Trickle irrigation, 4:1-48 Truffle cultivation, 16:71-107 Tuber, potato, 14:89-188 Tuber and root crops, see Root and tuber crops Tulip, see Bulb crops fertilization, 5:364-366 in vitro, 18:144-145 physiology, 5:45-125 Tunnel (cloche), 7:356-357 Turfgrass, fertilization, 1:112-117 Turnip, fertilization, 1:123-124 Turnip Mosaic Virus, 14:199-238 U

Urd bean, genetics, 2:364-373 Urea, foliar application, 6:332

v Vaccinium, 10:185-187. See also Blueberry; Cranberry Vase solutions, 3:82-95; 10:46-51 Vegetable crops: aroids, 8:43-99; 12:166-170 asparagus postharvest, 12:69-155 cactus, 18:300-302 cassava, 12:158-166; 13:105-129

273

CA storage, 1:337-394 CA storage diseases, 3:412-461 CA storage and quality, 8:101-127 chilling injury, 15:63-95 fertilization, 1:117-124 fluid drilling of seeds, 3:1-58 greenhouse management, 21:1-39 greenhouse pest management, 13:1-66

honey bee pollination, 9:251-254 hydroponics, 7:483-558 low-temperature sweetening, 17:203-231

minor root and tubers, 12:184-188 mushroom cultivation, 19:59-97 mushroom spawn, 6:85-118 nondestructive postharvest quality evaluation, 20:1-119 okra, 21:41-72 potato tuberization, 14:89-188 seed conditioing, 13:131-181 seed priming, 16:109-141 sweet potato, 12:170-176 tomato fruit ripening, 13:67-103 tomato parthenocarpy, 6:65-84 truffle cultivation, 16:71-107 yam (Dioscorea), 12:177-184 Vegetative tissue, desiccation tolerance, 18:176-195 Vernalization, 4:117, 15:284-287; 17:73-123

Vertebrate pests, 6:253-285 Vigna, see Cowpea genetics, 2:311-394 U.S. production, 12:197-222 Virus: benefits in horticulture, 3:394-411

elimination, 7:157-200; 9:318; 18:113-123

fig, 12:474-475 tree short life, 2:50-51 turnip mosaic, 14:199-238 Volatiles, 17:43-72 Vole, 6:254-274


274

w

x

Walnut, in vitro culture, 9:312 Water relations: cut flower, 3:61-66; 18:1-85 deciduous orchards, 21:105-131 desiccation tolerance, 18:171-213 fertilization, greenhouse crops, 5:332 fruit trees, 7:301-344 kiwifruit, 12:332-339 light in orchards, 2:248-249 photosynthesis, 11:124-131 trickle irrigation, 4:1-48 Watercore, 6:189-251 pear, 11:385-387 Watermelon, fertilization, 1:124 Weed control, ginseng, 9:228-229 Weeds: lettuce research, 2:198 virus, 3:403 Woodchuck,6:276-277 Woody species, somatic embryogenesis, 10:153-181

Xanthomonas phaseoli, 3:29-32,41, 45-46 Xanthophyll cycle, 18:226-239 Xanthosoma, 8:45-46, 56-57. See also Aroids

y Yam (Dioscorea), 12:177-184 Yield: determinants, 7:70-74; 97-99 limiting factors, 15:413-452

z Zantedeschia, see Aroids, ornamental Zinc: deficiency and toxicity symptoms in fruits and nuts, 2:151 foliar application, 6:332, 336 nutrition, 5:326 pine bark media, 9:124

Cumulative Contributor Index (Volumes 1-21) Abbott, J.A., 20:1 Adams III, W.W., 18:215 Aldwinckle, H.S., 1:423; 15:xiii Anderson, I.e., 21:73 Anderson, J.L., 15:97 Anderson, P.e., 13:257 Andrews, P.K., 15:183 Ashworth, KN., 13:215 Asokan, M.P., 8:43 Atkinson, D., 2:424 Aung, L.H., 5:45 Bailey, W.G., 9:187 Baird, L.A.M., 1:172 Banks, N.H., 19:217 Barden, J.A., 9:351 Barker, A.V., 2:411 Bass, L.N., 2:117 Becker, J.S., 18:247 Beer, S.V., 1:423 Behboudian, M.H., 21:105 Bennett, A.B., 13:67 Benschop, M., 5:45 Ben-Ya'acov, A., 17:381 Benzioni, A., 17:233 Bewley, J.D., 18:171 Binzel, M.L., 16:33 Blanpied, G.D., 7:xi Bliss, F.A., 16:xiii Borochov, A., 11:15 Bower, J.P., 10:229 Bradley, G.A., 14:xiii Brennan, R, 16:255 Broschat, T.K., 14:1 Brown, S. 15:xiii Buban, T., 4:174

Bukovac, M.J., 11:1 Burke, M.J., 11:xiii Buwalda, J.G., 12:307 Byers, RK, 6:253 Caldas, L.S., 2:568 Campbell, L.E., 2:524 Cantliffe, D.J., 16:109, 17:43 Carter, G., 20:121 Carter, J.V., 3:144 Cathey, H.M., 2:524 Chambers, RJ., 13:1 Charron, C.S., 17:43 Chin, e.K., 5:221 Clarke, N.D., 21:1 Cohen, M., 3:394 Collier, G.F., 4:49 Collins, W.L., 7:483 Compton, M.K, 14:239 Conover, e.A., 5:317; 6:119 Coppens d'Eeckenbrugge, G., 21:133 Coyne, D.P., 3:28 Crane, J.e., 3:376 Criley, RA., 14:1 Crawly, W., 15:1 Cutting, J.G., 10:229 Daie, J., 7:69 Dale, A., 11:185; 16:255 Darnell, RL., 13:339 Davenport, T.L., 8:257; 12:349 Davies, F.S., 8:129 Davies, P.J., 15:335 Davis, T.D., 10:63 DeGrandi-Hoffrnan, G., 9:237 De Hertogh, A.A., 5:45; 14:57; 18:87 275

276

CUMULATIVE CONTRIBUTOR INDEX

Deikman, J., 16:1 DellaPenna, D., 13:67 Demmig-Adams, B., 18:215 Dennis, F.G., Jr., 1:395 Doud, S.L., 2:1 Duke, S.O., 15:371 Dunavent, M.G., 9:103 Duval, M.-F., 21:133 Diizyaman, K, 21:41 Dyer, W.K, 15:371

Goszczynska, D.M., 10:35 Grace, S.c., 18:215 Graves, c.J., 5:1 Gray, D., 3:1 Grierson, W., 4:247 Griffen, G.J., 8:291 Grodzinski, B., 7:345 Gucci, R., 21:177 Guest, D.L, 17:299 Guiltinan, M.J., 16:1

Early, J.D., 13:339 Elfving, D.C., 4:1; 11:229 El-Goorani, M.A., 3:412 Esan, KB., 1:1 Evans, D.A., 3:214 Ewing, KK, 14:89

Hackett, W.P., 7:109 Hallett, I.C., 20:121 Halevy, A.H., 1:204; 3:59 Hammerschmidt, R, 18:247 Hanson, KJ., 16:255 Harker, F.R, 20:121 Heaney, RK., 19:99 Heath, RR, 17:43 Helzer, N.L., 13:1 Hendrix, J.W., 3:172 Henny, RJ., 10:1 Hergert, G.B., 16:255 Hess, F.D., 15:371 Heywood, V., 15:1 Hogue, KJ., 9:377 Holt, J.S., 15:371 Huber, D.J., 5:169 Hunter, KL., 21:73 Hutchinson, J.F., 9:273

Faust, M., 2:vii, 142; 4:174; 6:287; 14:333; 17:331; 19:263 Fenner, M., 13:183 Fenwick, G.R, 19:99 Ferguson, A.R, 6:1 Ferguson, LB., 11:289 Ferguson, L., 12:409 Ferree, D.C., 6:155 Ferreira, J.F.S., 19:319 Fery, RL., 2:311; 12:157 Fischer, RL., 13:67 Flick, C.E., 3:214 Flore, J.A., 11:111 Forshey, c.G., 11:229 Fujiwara, K., 17:125 Geisler, D., 6:155 Geneve, RL., 14:265 George, W.L., Jr., 6:25 Gerrath, J.M., 13:315 Giovannetti, G., 16:71 Giovannoni, J.J., 13:67 Glenn, G.M., 10:107 Goffinet, M.C., 20:ix Goldschmidt, KK, 4:128 Goldy, RG., 14:357 Goren, R, 15:145

Isenberg, F.M.R, 1;337 Iwakiri, B.T., 3:376 Jackson, J.K, 2:208 Janick, J., l:ix; 8:xi; 17:xiii; 19:319; 21:xi Jarvis, W.R, 21:1 Jensen, M.H., 7:483 Jeong, B.R, 17:125 Jewett, T.J., 21:1 Joiner, J.N., 5:317 Jones, H.G., 7:301 Jones, J.B., Jr., 7:1 Jones, RB., 17:173


Kagan-Zur, V., 16:71 Kang, S.-M., 4:204 Kato, T., 8:181 Kawa, L., 14:57 Kawada, K, 4:247 Kelly, J.F., 10:ix Khan, A.A., 13:131 Kierman, J., 3:172 Kim, K-W., 18:87 Kinet, ].-M., 15:279 King, G.A., 11:413 Kingston, CM., 13:407 Kliewer, W.M., 14:407 Knight, RJ., 19:xiii Knox, RB., 12:1 Kofranek, A.M., 8:xi Korcak, RF., 9:133; 10:183 Kozai, T., 17:125 Krezdorn, A.H., l:vii Lakso, A.N., 7:301; 11:111 Lamb, RC, 15:xiii Lang, G.A., 13:339 Larsen, RP., 9:xi Larson, RA., 7:399 Leal, F., 21:133 Ledbetter, CA., 11:159 Li, P.H., 6:373 Lill, RK, 11:413 Lipton, W.]., 12:69 Litz, R.K, 7:157 Lockard, RG., 3:315 Loescher, W.H., 6:198 Lorenz, O.A., 1:79 Lu, R, 20:1 Lyrene, P., 21:xi Maraffa, S.B., 2:268 Marangoni, A.G., 17:203 Marini, RP., 9:351 Marlow, G.C, 6:189 Maronek, D.M., 3:172 Martin, G.G., 13:339 Mayak, 5., 1:204; 3:59 Maynard, D.N., 1:79

277

McConchie, R, 17:173 McNicol, RJ., 16:255 Merkle, S.A., 14:265 Michailides, T.]., 12:409 Michelson, K, 17:381 Mika, A., 8:339 Miller, 5.5., 10:309 Mills, H.A., 2:411; 9:103 Mills, T.M., 21:105 Mitchell, CA., 17:1 Mizrahi, Y., 18:291, 321 Molnar, J.M., 9:1 Monk, G.]., 9:1 Monselise, S.P., 4:128 Moore, G.A., 7:157 Mor, Y., 9:53 Morris, J.R, 16:255 Murashige, T., 1:1 Murray, S.H., 20:121 Myers, P.N., 17:1 Nadeau, ].A., 19:1 Neilsen, G.H., 9:377 Nerd, A., 18:291, 321 Niemiera, A.X., 9:75 Nobel, P.S., 18:291 O'Donoghue, KM., 11:413 Ogden, R]., 9:103 O'Hair, S.K., 8:43; 12:157 Oliveira, CM., 10:403 Oliver, M.J., 18:171 O'Neill, S.D., 19:1 Opara, L.U., 19:217 Ormrod, D.P., 8:1 Palser, B.F., 12:1 Papadopoulos, A.P., 21:1 Pararajasingham, 5., 21:1 Parera, CA., 16:109 Pegg, K.G., 17:299 Pellett, H.M., 3: 144 Perkins-Veazil, P., 17:267 Ploetz, RC, 13:257 Pokorny, F.A., 9:103

278

Poole, RT., 5:317;6:119 Poovaiah, B.W., 10:107 Portas, CA.M., 19:99 Porter, M.A., 7:345 Possingham, J.V., 16:235 Pratt, C, 10:273; 12:265 Preece, J.K, 14:265 Priestley, CA., 10:403 Proctor, J.T.A., 9:187 Quamme, H., 18:xiii Raese, J.T., 11:357 Ramming, D.W., 11:159 Reddy, A.S.N., 10:107 Redgwell, RJ., 20:121 Reid, M., 12:xiii, 17:123 Reuveni, M., 16:33 Richards, D., 5:127 Rieger, M., 11:45 Roper, T.R, 21:215 Rosa, KA.S., 19:99 Roth-Bejerano, N., 16:71 Roubelakis-Angelakis, K.A., 14:407 Rouse, J.L., 12:1 Royse, D.J., 19:59 Rudnicki, RM., 10:35 Ryder, KJ., 2:164; 3:vii Sachs, R, 12:xiii Sakai, A., 6:357 Salisbury, F.B., 4:66; 15:233 San Antonio, J.P., 6:85 Sankhla, N., 10:63 Saure, M.C, 7:239 Schaffer, B., 13:257 Schneider, G.W., 3;315 Schuster, M.L., 3:28 Scorza, R, 4: 106 Scott, J.W., 6:25 Sedgley, M., 12:223 Seeley, S.S., 15:97 Serrano Marquez, C, 15:183 Sharp, W.R, 2:268; 3:214 Shattuck, V.I., 14:199


Shear, CB., 2:142 Sheehan, T.J., 5:279 Shipp, J.L., 21:1 Shirra, M., 20:267 Shorey, H.H., 12:409 Simon, J.K, 19:319 Sklensky, D.K, 15:335 Smith, G.S., 12:307 Smock, RM., 1:301 Sommer, N.F., 3:412 Sondahl, M.R, 2:268 Sopp, P.L, 13:1 Soule, J., 4:247 Sparks, D., 8:217 Splittstoesser, W.K, 6:25; 13:105 Srinivasan, C, 7:157 Stang, KJ., 16:255 Steffens, G.L., 10:63 Stevens, M.A., 4:vii Stroshine, RL., 20:1 Struik, P.C, 14:89 Studman, CJ., 19:217 Stutte, G.W., 13:339 Styer, D.J., 5;221 Sunderland, K.D., 13:1 Suninyi, D., 19:263 Swanson, B., 12:xiii Swietlik, D., 6:287 Syvertsen, J.P., 7:301 Tattini, M., 21:177 Tetenyi, P., 19:373 Tibbitts, T.W., 4:49 Timon, B., 17:331 Tindall, H.D., 16:143 Tisserat, B., 1:1 Titus, J.S., 4:204 Trigiano, RN., 14:265 Tunya, G.O., 13:105 Upchurch, B.L., 20:1 van Doorn, W.G., 17:173; 18:1 Veilleux, RK, 14:239 Vorsa, N., 21:215


Wallace, A., 15:413 Wallace, D.H., 17:73 Wallace, G.A., 15:413 Wang, c.Y., 15:63 Wang, S.Y., 14:333 Wann, S.R, 10:153 Watkins, C.B., 11:289 Watson, G.W., 15:1 Webster, B.D., 1:172; 13:xi Weichmann, J., 8:101 Wetzstein, H.Y., 8:217 Whiley, A.W., 17:299 Whitaker, T.W., 2:164 White, J.W., 1:141 Williams, E.G., 12:1 Williams, M.W., 1:270 Wismer, W.V., 17:203

279

Wittwer, S.H., 6:xi Woodson, W.R, 11:15 Wright, RD., 9:75 Wutscher, H.K., 1:237 Yada, RY., 17:203 Yadava, D.L., 2:1 Yahia, E.M., 16:197 Yan, W., 17:73 Yarborough, D.E., 16:255 Yelenosky, G., 7:201 Zanini, E., 16:71 Zieslin, N., 9:53 Zimmerman, RH., 5:vii; 9:273 Zucconi, F., 11:1

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