HORTICULTURAL REVIEWS
Volume 28
Horticultural Reviews is sponsored by: American Society for Horticultural Science
Editorial Board, Volum.e 28 Carole E. Bassett Steve van Nocker Rodomiro Ortiz
HORTICULTURAL REVIEWS Volume 28
edited by
Jules Janick Purdue University
John Wiley &- Sons, Inc. NEW YORK / CHICHESTER / WEINHEIM / BRISBANE / SINGAPORE / TORONTO
This book is printed on acid-free paper. § Copyright © 2003 by John Wiley & Sons, New York. All rights reserved. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY 10158-0012, (212) 850-6011, fax (212) 850-6008, E-Mail:
[email protected]. 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 professional services. If professional advice or other expert assistance is required, the services of a competent professional person should be sought. Library of Congress Cataloging-in-Publication Data: ISBN: 0-471-21542-2 ISSN: 0163-7851
10 9 8 76 5 4 3 2 1
Contents Contributors Dedication: M. Allen Stevens
viii xi
Fredrick A. Bliss 1. Plant Nomenclature and Taxonomy:
An Horticultural and Agronomic Perspective
1
David M. Spooner, Wilbert L. A. Hetterscheid, Ronald G. van den Berg, and Willem Brandenburg I. II.
III. IV. V. VI. VII. VIII. IX. X.
Introduction Species Concepts in Wild Plants Classification Philosophies in Wild and Cultivated Plants Brief History of Nomenclature and Codes Fundamental Differences in the Classification and Nomenclature of Cultivated and Wild Plants A Comparison of the ICBN and ICNCP Possible New Codes Cultivated Plant Nomenclature and the Law Cultivar Epithets and Trademarks Recommendations for a Universally Stable Crop Nomenclature Through Changes and Use of the ICNCP References Literature Cited
2 11 20 29 33 39 45 48 49
50 51 53
2. Grafting of Herbaceous Vegetable
and Ornamental Crops
61
Jung-Myung Lee and Masayuki Oda I. II.
Introduction Grafting Technology
63 65 v
CONTENTS
vi
III. IV. V. VI.
Physiology of Grafting Crop Examples Grafting for Crop Improvement Conclusion and Prospects Literature Cited
78 84 109 115 116
3. Health Promoting Phytochemicals in Vegetables Mosbah M. Kushad, John Masiunas, Kathy Eastman, Wilhelmina Kalt, and Mary A. L. Smith
125
Introduction Major Classes of Phytochemicals in Vegetable Phytochemicals Content and Health Benefits of the Four Major Vegetable Groups Conclusions and Future Research Needs Literature Cited
126 129
I. II. III. IV.
150 165 166
4. Detection and Elimination of Viruses and
Phytoplasmas from Pome and Stone Fruit Trees
187
Margit Laimer I. II. III. IV. V. VI. VII.
Introduction Pathogens Pathogen Detection Elimination of Viruses Elimination of Phytoplasmas Indexing, Mass Propagation, and Germplasm Conservation Conclusions Literature Cited
5. Pear Fruit Volatiles Francesca Rapparini and Stefano Predieri I. II. III. IV. V.
Introduction Analysis of Chemical Composition Biogenesis Factors Affecting Qualitative and Quantitative Emission of Pear Volatiles Volatile Compounds' Influence on Quality
189 191 198 205 218 219 221 224
237 239 241 279 289 303
vii
CONTENTS
VI.
Summary and Conclusions Literature Cited
6. The Physiology of Flowering in Strawberry
Rebecca 1. Darnell, Daniel J. Cantliffe, Daniel S. Kirschbaum, and Craig K. Chandler I. II. III. IV. V. VI.
Introduction Floral Morphology Environmental Effects on Reproductive Growth Floral Induction Models Genetics of Floral Induction Conclusions Literature Cited
306 308 325
326 326 327 333 342 344 345
7. Flower and Fruit Thinning of Peach
and other Prunus
351
Ross E. Byers, Guglielmo Costa, and Giannina Vizzotto I. II. III. IV. V.
Introduction Reproductive Physiology Abscission Thinning Practices Future Prospects Literature Cited
352 355 362 365 383 384
8. The Reproductive Biology of the Lychee
393
Raphael A. Stern and Shmuel Gazit I. II. III. IV. V. VI.
Introduction Flowering Pollination The Fertilization Process and Initial Fruit Set Fruit Development and Abscission Concluding Remarks Literature Cited
394 397 422 428 433 443 444
Subject Index
454
Cumulative Subject Index
456
Cumulative Contributor Index
478
Contributors Fredrick A. Bliss, Seminis, Vegetable Seeds, Woodland, CA, 95695 Willem Brandenburg, Plant Research International, PO Box 16, 6700 AA Wageningen, The Netherlands Ross E. Byers, Department of Horticulture, Virginia Polytechic Institute and State University, Alson H. Smith Jr. Agricultural Research and Extension Center, 595 Laurel Grove Road, Winchester, VA, 22602 Daniel J. Cantliffe, Horticultural Sciences, University of Florida, P.O. Box 110690, Gainesville, FL, 32611 Craig K. Chandler, Gulf Coast Research and Education Center, University of Florida, 13138 Lewis Gallagher Road, Dover, FL, 33527 Guglielmo Costa, Dipartmento di Colture Arboree, University of Bologna, Via Fanin 50, Bologna, 40126, Italy Rebecca L. Darnell, Horticultural Sciences, University of Florida, P.O. Box 110690, Gainesville, FL, 32611 Kathy Eastman, Center for Economic Entomology, Illinois Natural History Survey, University of Illinois, 172 Natural Resources Building, 607 East Peabody Drive, Champaign, IL, 61820 Shmuel Gazit, The Kennedy-Leigh Center for Horticultural Research, The Hebrew University of Jerusalem, Faculty of Agriculture, PO Box 12, Rehovot, 76100, Israel Wilbert L. A. Hetterscheid, VKC/NDS, Linnaeuslaan 2a, 1431 JV Aalsmeer, The Netherlands Wilhelmina Kalt, Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Center, Kentville, Nova Scotia, B4N lJ5, Canada Daniel S. Kirshbaum, Horticultural Sciences, University of Florida, P.O. Box 110690, Gainesville, FL, 32611 Mosbah M. Kushad, Department of Natural Resources and Environmental Sciences, University of Illinois, 279 Madigan Laboratory, 1201 West Gregory Drive, Champaign, IL, 61801 Margit Laimer, Plant Biotechnology Unit, Institute of Applied Microbiology, University of Agricultural Sciences, Nussdorfer Lande 11, 1190, Vienna, Austria,
[email protected] Jung-Myung Lee, Kyung Hee University, Department of Horticulture, Suwon, 449-701, Korea John Musiunas, Department of Natural Resources and Environmental Sciences, University of Illinois, 279 Madigan Laboratory, 1201 West Gregory Drive, Champaign, IL, 61801 Masayuki Oda, Osaka Prefecture University, Graduate School of Agriculture and Biological Science, Sakai, Osaka, 599-8531, Japan Stefano Predieri, Istituto di Biometeorologia-Firenze, Sezione di Bologna, Via Gobetti 101,40129 Bologna, Italy viii
CONTRIBUTORS
ix
Francesca Rapparini, Istituto di Biometeorologia-Firenze, Sezione di Bologna, Via Gobetti 101, 40129 Bologna, Italy Mary A. L. Smith, Department of Natural Resources and Environmental Sciences, University of Illinois, 1021 Plant Sciences Laboratory, 1201 South Dorner Drive, Champaign, IL, 61801 David M. Spooner, USDA, Agricultural Research Service, Vegetable Research Unit, Department of Horticulture, University of Wisconsin, 1575 Linden Drive, Madison, WI, 53706-1590 Raphael A. Stern, MIGAL, Galilee Technology Center, PO Box 90000, Rosh Pina, 12100, Israel Ronald G. van den Berg, Biosystematics Group, Department of Plant Sciences, Wageningen University, PO Box 8010,6700 ED Wageningen, The Netherlands Giannina Vizzotto, Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Udine University, Via delle Scienze 208, Udine, 33100, Italy
M. Allen Stevens
Dedication: M. Allen Stevens Allen Stevens' distinguished career in horticulture covers over 30 years in agricultural research. He spent nearly a decade each at the University of California, Davis, the Campbell Soup Company, and Petoseed Co., now Seminis Vegetable Seeds. He once remarked to me that after about ten years, he was ready for new challenges. The changes in venue served him well, because he met each new opportunity with enthusiasm and his accomplishments attest to his success. At UC Davis where he held the title of Geneticist and Professor, he and coworkers published over 100 scientific articles and book chapters. They received well-deserved recognition through the National Canners Association Award, 1968 and 1977; the Asgrow Award, 1971 and 1978; the National Food Processors Association Award, 1980; and the Homer C. Thompson Award, 1983. While at the university, he was advisor to graduate students in plant breeding and genetics as a major professor and member of numerous graduate degree committees. Allen has especially enjoyed working with young breeders, to whom he emphasized the importance of the art of plant breeding and the "eye" for selecting those rare recombinants with exceptional promise as well as application of sound scientific principles. He understood the practical nature of the seed trade and realized that broad knowledge of horticulture and close personal contact with growers, processors, and consumers were essential to success but often under-appreciated. It was enjoyable and a great learning experience to evaluate field trials with him and see the fine points that others often overlooked. His contributions as a plant breeder spanned both public and private sectors and include development of the outstanding processing tomato cultivar, 'UC82,' which was grown worldwide, and 'UC204,' 'Alta,' 'Lassen,' and 'Shasta,' which were leaders in California. A westerner at heart, Allen is really at home west of the Rockies. He was born and raised in southern Utah; graduated from Utah State University, receiving the BS degree (Agronomy) in 1957, and the MS degree (Soil Fertility) in 1961. Following his first degree, he served as a pilot in the U.S. Army. Allen worked as an Extension Agent in Oregon, then studied with the late William A. (Tex) Frazier at Oregon State University, where he received his doctorate in horticulture. His graduate studies xi
xii
DEDICATION: M. ALLEN STEVENS
about the chemistry and genetics of flavor in snap beans set the theme for many of his subsequent contributions to breeding vegetable crops for greater productivity and improved nutritional and organoleptic traits. Fittingly, he pursued these topics as a tomato breeder in the Department of Vegetable Crops at UC Davis and the Campbell Soup Company, and continued to give support as a research administrator. Although the value of breeding for better quality and improved nutritive content in vegetables and fruits has long been recognized among researchers, it has been a difficult concept to incorporate into commercial varieties, often because of limited interest from consumers. Times may be changing, however, as the value of improved nutritional content is more widely recognized. If so, his pioneering work may be rediscovered. No one better understands the importance of diverse germplasm for a successful breeding program than Allen. He was particularly interested in and gave support for conservation and use of plant genetic resources. He served as a member of the National Plant Genetic Resources Board and Board of Directors of the Genetic Resources Communications System in the United States. As Chair of the University of California Tomato Genetic Resources Task Force, he played a major role in establishing an endowment fund for support of the Charles M. Rick Tomato Genetic Resource Center located at UC Davis. In recognition of that and other important contributions to the University of California and California agriculture, Allen received the Award of Distinction, from the College of Agricultural and Environmental Sciences at UC Davis in 1995. His plant breeding, research, administration and service activities are known around the world. He was a visiting scientist at the Hebrew University in Rehovot, Israel. For the Asian Vegetable Research and Development Center located in Taiwan, he served as USAID Scientific Liaison Officer and a member of the Board of Trustees. He had global responsibilities for R&D at the Campbell Soup Company and Seminis Vegetable Seeds and served on the Executive Committee of the International Food Biotechnology Council. He was consultant to the FAO of the United Nations and to USAID on vegetable production and improvement. Allen has been a visionary and inspiring leader in professional organizations that represent their respective fields of influence in agriculture. He has participated in most facets of the American Society for Horticultural Science at one time or another, where he served as Vice President of both the Research and Industry Divisions, as President in 1993, and as Chairman of the Board of Directors when he organized the strategic planning initiative. That provided an important blueprint for the Society to better serve an ever-changing membership. He is an elected
DEDICATION: M. ALLEN STEVENS
xiii
Fellow of the American Society for Horticultural Science and the American Association for the Advancement of Science. I first became acquainted with Allen by reading about his research on flavor components of snap beans, which he conducted as a graduate student at Oregon State University in the early 1960s. Later, I referred to that information periodically as I looked for new opportunities for bean improvement. The 'Bush Blue Lakes' beans that came from the OSU program are still remembered as standards for high quality. It has been my pleasure to work with him on numerous committees and task forces dealing with topics covering germplasm resources, intellectual property rights, and education of plant breeding students, as well as many activities within the American Society for Horticultural Science. In 1998 as Vice President for Research and Development, he asked me to join Seminis Vegetable Seeds, where I had the opportunity to work with him daily. I, like many others, had the good fortune to draw on his great breadth of knowledge about practical vegetable breeding and the commercial seed business. Since his retirement from the position of Vice President of Research & Development at Seminis, he and his wife Hermese have considerably more time for extensive travel-now for enjoyment, rather than mainly for business. They have the opportunity to see more of their children and grandchildren and to revisit family and friends and the land he knew as a youngster in Utah. In addition to being an accomplished breeder, scientist, and administrator, Allen is a superb amateur photographer, displaying professional skill and standards of quality and accomplishment similar to those he displayed as a professional horticulturist. Don't be surprised if you see some of his beautiful photographs in the popular press. Fredrick A. Bliss Seminis Vegetable Seeds Woodland, CA 95695
1
Plant Nomenclature and Taxonomy An Horticultural and Agronomic Perspective David M. Spooner* U.S. Department of Agriculture Agricultural Research Service Vegetable Crops Research Unit Department of Horticulture University of Wisconsin 1575 Linden Drive Madison Wisconsin 53706-1590 Wilbert L. A. Hetterscheid VKC/NDS Linnaeuslaan 2a 1431 JV Aalsmeer The Netherlands
Ronald G. van den Berg Biosystematics Group Department of Plant Sciences Wageningen University PO Box 8010 6700 ED Wageningen The Netherlands Willem A. Brandenburg Plant Research International PO Box 16 6700 AA, Wageningen The Netherlands
I. INTRODUCTION A. Taxonomy and Systematics B. Wild and Cultivated Plants II. SPECIES CONCEPTS IN WILD PLANTS A. Morphological Species Concepts B. Interbreeding Species Concepts C. Ecological Species Concepts D. Cladistic Species Concepts E. Eclectic Species Concepts F. Nominalistic Species Concepts
*The authors thank Paul Berry, Philip Cantino, Vicki Funk, Charles Heiser, Jules Janick, Thomas Lammers, and Jeffrey Strachan for review of parts or all of our paper.
Horticultural Reviews, Volume 28, Edited by Jules Janick ISBN 0-471-21542-2 © 2003 John Wiley & Sons, Inc. 1
2
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
III. CLASSIFICATION PHILOSOPHIES IN WILD AND CULTIVATED PLANTS A. Wild Plants B. Cultivated Plants IV. BRIEF HISTORY OF NOMENCLATURE AND CODES V. FUNDAMENTAL DIFFERENCES IN THE CLASSIFICATION AND NOMENCLATURE OF CULTIVATED AND WILD PLANTS A. Ambiguity of the Term Variety B. Culton Versus Taxon C. Open Versus Closed Classifications VI. A COMPARISON OF THE ICBN AND ICNCP A. Nomenclatural Types and Standards B. Denomination Classes and the Reuse of Epithets C. Botanical Hybrid (Species) Names D. The Species Category in Cultivated Plant Taxonomy (Cultonomy) E. The (Notho-)Genus Category in Cultivated Plant Taxonomy (Cultonomy) F. Ties Between the ICBN and ICNCP VII. POSSIBLE NEW CODES A. Biocode B. PhyloCode VIII. CULTIVATED PLANT NOMENCLATURE AND THE LAW IX. CULTIVAR EPITHETS AND TRADEMARKS X. RECOMMENDATIONS FOR A UNIVERSALLY STABLE CROP NOMENCLATURE THROUGH CHANGES AND USE OF THE ICNCP REFERENCES LITERATURE CITED
I. INTRODUCTION Now the whole world had one language and a common speech. Then they said, "Come, let us build ourselves a city, with a tower that reaches to the heavens, so that we may make a name for ourselves and not be scattered over the face of the whole earth." The Lord said, "Come, let us go down and confuse their language so they will not understand each other." So the Lord scattered them from there over all the earth, and they stopped building the city. That is why it was called Babel becaOuse there the Lord confused the language of the whole world. (Genesis 11 :1, 3, 4, 6-9; New International Bible)
Communication of taxonomists to agronomists and horticulturists can be hindered by specialized terminology that aids concise and effective communication of complex ideas among taxonomists, but may seem intractable and pedantic to agriculturalists. Our goals in this review are to provide agronomists and horticulturists basic conceptual tools of taxonomy: (1) to help understand the taxonomic classification in wild and cultivated plants; (2) to question whether the concept underlying this
1. PLANT NOMENCLATURE AND TAXONOMY
3
taxonomy is appropriate; (3) to help understand why new data may require changes in nomenclature; and (4) place the taxonomy of crops in the context of legal requirements that depend on a taxonomic name. Different taxonomic concepts of wild plants and cultivated plants are reviewed because both classes are used in breeding and germplasm evaluation. The goals and practices of two codes of plant nomenclature, the International Code of Botanical Nomenclature (ICBN) and the International Code of Nomenclature for Cultivated Plants (ICNCP) are compared, the former (Greuter et al. 2000) used primarily for wild plants, and the latter (Trehane et al. 1995) used exclusively for cultivated plants. The plethora of specialized terms used in this review is presented as a glossary in Table 1.1. Table 1.1
Glossary of terms used highlighted in bold italic in the text.
artificial classification. Classification that may be based on any special-purpose criteria that users view as relevant to group plants, not based on evolutionary relationships (see natural classification). basionym. The original name of a taxon, which may be changed in rank, say from variety to species. For example, when Solanum jamesii Bitter var. brachistotrichium Bitter was recognized as a species, its name became Solanum brachistotrichium (Bitter) Rydb., but the basionym remains Solanum jamesii Bitter var. brachistotrichium Bitter. biological species concept. The concept of a species as a population or group of populations that freely interbreed but are reproductively isolated from other populations. biosystematics. A term that originally referred to the use of breeding programs (by biosystematists) to infer evolutionary relationships among organisms; the term later became broadened to refer to a wide variety of experimental data gathering programs. cenospecies. Assemblages of related ecospecies that when crossed produce highly to completely sterile hybrids. cladogram. A branching phylogenetic tree of individuals or taxa, rooted on an outgroup(s) produced by a method that minimizes evolutionary changes (by parsimony, maximum likelihood, or other methods) of characters believed to be homologous among a group of organisms. cladistic species concepts. A philosophy and set of methods that use cladistic criteria to determine the limits of species. closed classification system. Hierarchical system where the categories at every rank are totally filled up by the sum of the categories at the next lower rank. comparium. A group of related cenospecies that cannot be crossed with one another. ecological species concepts. A philosophy that ecological factors are primary in forming and maintaining a species. (continues)
4
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
Table 1.1
(continued)
compilospecies. Genetically aggressive, highly polymorphic species, often of complex hybrid origin, often containing more than one ploidy level, often very weedy, and obscuring other species boundaries. conservation. In order to avoid disadvantageous changes in the nomenclature of families, genera, and species entailed by the strict application of nomenclatural rules, and especially of the principle of priority, names may be retained as legitimate even though initially they may have been illegitimate, by petitioning in the journal Taxon, and later vote at the International Botanical Congress. Conservation operates only within the taxa in which they have been voted upon, and is not operative if the taxon is classified in another group. convariety (convar). A group of cultivars. These can be roughly comparable to cultivar groups, but convarieties, unlike cultivar groups, do not necessarily contain named varieties, and convarieties are members of traditional "Linnaean" ranks. The ICNCP replaced this term with the term cultivar-group, and convarieties should not be used in modern cultivated plant taxonomy. crop. The total of all cultivars/cultivar-groups that constitute an agricultural, horticultural, or silvicultural product; examples: potato, cabbage, or tulips. cytodemes. Groups of plants characterized by having a constant chromosome number, with all accessions of the same cytodeme being fully interfertile, while those of different cytodemes are essentially cross-sterile. cultigen. A taxon with only cultivated representatives; example: Triticum aestivum, the species name encompassing all hexaploid wheat varieties. cultivar. A systematic group of cultivated plants that is clearly distinct, uniform, and stable in its characteristics and which, when propagated by appropriate means, retains these characteristics. cultivar-group. A group of properly named cultivars, based on one or more criteria. cultivated plant. One whose origin or selection is primarily due to the intentional activities of mankind. Such a plant may arise either by deliberate or, in cultivation, accidental hybridization, or by selection from existing cultivated stock, or may be a selection from minor variants within a wild population and maintained as a recognizable entity solely by deliberate and continuous propagation (Trehane et al. 1995). culton. A systematic group of cultivated plants; there are two types of culta: the cultivar and the cultivar-group. cultonomy. Cultonomy is the entire body of principles, philosophies, and methodologies leading to classifications of cultivated plants into culta, and following the rules of ICNCP. dendrogram. A branching diagrammatic representation of a set of individuals or taxa, constructed from overall similarity of a set of characters among organisms, which generally is not provided any phylogenetic interpretation. denomination class. Agreed upon systematic group (often a genus) within which a cultivar epithet may only be used once.
1. PLANT NOMENCLATURE AND TAXONOMY
Table 1.1
5
(continued)
eclectic species concepts. A philosophy that species are defined, formed, and maintained by a variety of biological factors, including morphological, interbreeding, ecological, and phylogenetic factors. ecospecies. An assemblage of ecotypes and are separated by incomplete sterility barriers. ecotype. All members of a species fitted to survive in a particular environment; different ecotypes within species have no interbreeding barriers. epithet. Part of the full name of a species; a complete species name consists of the name of the genus to which the species belongs, plus the specific epithet, plus the author of the species. form. The lowest rank in the taxonomic hierarchy (below variety), meant to convey minor variants in nature. gene pool classification. A classification of cultivated plants focused on the crossability of species to an individual crop plant, with gene pool 1 being the crop and those species easily crossable to it, gene pool 2 being species crossable to the crop with some difficulty, and gene pool 3 being species crossable to the crop with extreme difficulty. homologous. Characters that arise by common descent. ICBN. International Code of Botanical Nomenclature (latest version is Greuter et al. 2000). ICNCP. International Code of Nomenclature of Cultivated Plants (latest version is Trehane et al. 1995). ingroup. A putatively monophyletic group that is the prime subject of a cladistic analysis. indigen. Wild taxa in their natural habitat and distribution area. interbreeding species concepts. A philosophy and set of methods that define species almost entirely on the ability of species to exchange genes naturally or artificially, as assessed by artificial crossing programs, studies of mechanisms to facilitate gene flow, and biological isolating mechanisms. landrace. Cultivar that originated as a product of (the first stages of) mass selection (and not as a product of modern plant breeding), generally confined to a certain region. lumper. Refers to a taxonomist who focuses more on similarities than differences, discounting the importance of minor variation among individuals, and tending to recognize fewer taxa (see splitter). maximum likelihood. A set of methods used to construct cladograms based on certain evolutionary models of character state changes (compare to parsimony). monophyletic group. A group that includes an ancestral species and all of its descendants. morphological species concepts. A philosophy and set of methods that define species entirely on morphological or anatomical characters. natural classification. Classification based on the evolutionary relationships between the entities to be classified. (continues)
6
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
Table 1.1
(continued)
nomenclatural types. Objects (usually a herbarium sheet) to which a name of a taxon is permanently attached. When a species is described, a type specimen is designated that serves as a reference point for others to compare their concept of names. nominalistic species concepts. A philosophy that questions the very existence of species, and believes that individuals or interbreeding populations are the only population system with any objective reality. nothotaxon. A taxon of hybrid origin (as notho species, nothogenus). open classification. Nonhierarchical system of flexible groups that do not automatically need to be grouped together in larger groups, nor subdivided in smaller groups. orthologous. Genetic characters that are homologous from a speciation event, that is, identical by descent. outgroup. Any group used in a cladistic analysis that is not included in the taxon under study, which is used to root a phylogenetic tree. ordination plot. A phenetic analysis (as principal components analyses, principal coordinates analyses, multidimensional scaling analyses), showing overall similarity of individuals or taxa on two- or three-dimensional plots. paralogous. Characters that have arisen as a result of gene duplication. paraphyletic group. A nonmonophyletic group containing some, but not all representatives of a taxon; said another way, an incomplete group of descendants from one common ancestor with one or more descendants missing. parsimony. A set of methods that assumes that the simplest solution is the most likely one. It is used to construct cladograms, and assumes that minimizing the number of character state changes on a tree is the best approximation of phylogenetic history. plesiomorphy. An ancestral character, not viewed as useful in cladistic analyses for defining monophyletic groups. pluralist species view. The idea that species are formed and maintained by a variety of criteria including morphological, geographical, biological, and ecological criteria. polyphyletic group. A nonmonophyletic group where the common ancestor is placed in another taxon; in other words, a group in which the members do not ultimately derive from one common ancestor, where the descendants of one or more other groups are included. priority. A principle in the ICBN stating that the earliest validly published name is the proper name assigned to a species. sister group. The most closely related monophyletic outgroup to the ingroup. splitter. Refers to a taxonomist who focuses more on small differences among taxa, emphasizing minor variation among individuals, and who tends to recognize more taxa (see lumper). standard. A specimen, seed sample, or illustration kept and maintained in a conserved place to illustrate the diagnostic characteristics of a cultivar (used in the ICNCP).
1. PLANT NOMENCLATURE AND TAXONOMY
Table 1.1
7
(continued)
symplesiomorphy. A set of shared primitive characters, viewed as useless in cladistic analyses for defining monophyletic groups. synapomorphy. A set of shared derived characters, viewed as useful in cladistic analyses for defining monophyletic groups; said another way, characters shared by two or more taxa as a result of their immediate common ancestry. taxon. A systematic group of plants in a hierarchical system. total evidence analysis. A philosophy that cladistic analyses should be constructed with many separate sets of data. type (nomenclatural type). That element to which the name of a taxon is permanently attached, whether as a correct name or as a synonym (used in the ICBN). variety. A "botanical" variety is a rank in the taxonomic hierarchy below the rank of species and subspecies and above the rank of form (form/variety/subspecies/species). Another meaning, as used in legal texts is synonymous with cultivar (see Section V.A., Ambiguity of the Term Variety).
A. Taxonomy and Systematics A plant's name is the key to its literature. Van Steenis (1957)
One of the greatest assets of a sound classification is its predictive value. Mayr (1969)
Taxonomy is the theory and practice of describing, naming, and classifying organisms (Lincoln, Boxshall, and Clark 1998). Systematics is a related term, sometimes used synonymously, but involves a broader discipline of discovering phylogenetic relationships through modern experimental methods using comparative anatomy, cytogenetics, ecology, morphology, molecular data, or other data (Stuessy 1990). It also could be more generally defined as the science of developing methods and philosophies for the systematic grouping of organisms. Whatever term one chooses (we use taxonomy here for simplicity), taxonomists are basically involved with: (1) determining what is a species (or their subdivisions, as subspecies), (2) distinguishing these species from others through keys and descriptions and geographic boundaries and mapping their distributions, (3) investigating their interrelationships, and (4) determining proper names of species and higher order ranks (as
8
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
genera or families) using international rules of nomenclature. In addition, some taxonomists investigate processes of evolution that lead to the existing pattern of species and their interrelationships. There are many rationales for biological taxonomy, including the need (1) to understand the world about us and to conceptualize and order this through classifications; (2) to have classifications for identification and communication; (3) for a convenient information retrieval system; (4) to use stable names that maintain continuity of the literature; (5) to construct a predictive classification; and (6) to construct a useful framework to understand phylogenetic relationships. Taxonomy has special use for conservators including (7) to provide a useful reference system for biodiversity conservation; (8) to aid gene bank managers to rationally organize collections; (9) to aid germplasm collectors to plan expeditions based on gaps in a genebank (Warburton 1967; Mayr 1982; Stuessy 1990; Judd et al. 1999; Woodland 2000). For agriculturists and horticulturists, stability of names and prediction are major rationales, but the prediction rationale is controversial, as we shall discuss. The need for stable names is only amplified with crop plants where the frequency and need for information retrieval from the literature, through the convenient label of a species name, is much greater than for other plants. One reason for using Latin names or scientific names or Linnaean binomials for plants is to avoid the potential Babel of different common names for the same entity (synonyms). As we discuss, however, many factors are in conflict with this extremely practical goal of stability, leading to different scientific names for the same plant. What factors conflict with a stable nomenclature? 1. Different classification philosophies have fundamental differences
in primacy put on morphological, crossability, phylogenetic, ecological, molecular, or other data that may provide different names to taxa. 2. Powerful new technologies (molecular systematics and computer algorithms to analyze these data) are revising knowledge on species limits and species interrelationships. 3. Taxonomists are far from agreement between the often competing goals of stability of names and potentially improved predictivity of new classifications. 4. Revised phylogenetic data and emerging classification philosophies threaten to overturn long-held traditional classifications. Most users of taxonomy intuitively accept the putative predictive component of classifications (Mayr 1969). Claims of the predictive value of classifications can be found in Michener (1963), Rollins (1965), War-
1. PLANT NOMENCLATURE AND TAXONOMY
9
burton (1967), Sokal (1985), and Stuessy (1990). For example, Warburton (1967) states: [Prediction] means that one can describe a trait as characteristic of all members of a taxon before it has been verified for all. It also means that if organisms have been classified together as a taxon because they have all been found to share certain traits, they will later be found to share other traits as well.
For plant breeders, prediction would mean that germplasm could be chosen or avoided based on past positive or negative evaluations. Germplasm evaluations organized with species or higher ranks are common in the literature, for example, species-specific statements of breeding value of wild potato germplasm are found in Ross (1986), Hawkes (1990), and Ruiz de Galerreta et al. (1998). Clearly, not all accessions of a species share traits, but lacking prior evaluation data, taxonomy provides a useful guide to make inferences on unevaluated germplasm based on present knowledge. While differences in classification philosophies provide fascinating debate among taxonomists and advances the field, the remaining biological community largely focuses on stability of names for purely practical considerations. Some see a failure of the stability goal as the failure of taxonomists to fulfill their service role. Many taxonomists, however, focus on improved phylogenetic classifications as primary. B. Wild and Cultivated Plants Botanists have generally neglected cultivated varieties as beneath their notice.
Darwin (1868) Most modern taxonomists do next to nothing with cultivated plants; many deliberately avoid studying or even collecting them.
Anderson (1952) Almost one-third [of Conley K. McMullen's Flowering Plants of the Galapagos, 1999] covers cultivated species. That seems to place a rather excessive emphasis on the least interesting plants, but undoubtedly tourists will appreciate the information.
Ulloa Ulloa (2001)
Cultivated plants have various definitions, but all focus on the activities of humans. De Wet (1981) simply considered a cultivated plant one that
10
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
is adapted to the man-made habitat. Schwanitz (1967) defined cultivated plants as: the result of evolution processes, that were going on in prehistoric and historic times and are still going on nowadays, both under direct and indirect influence of mankind.
Trehane et al. (1995) defined a cultivated plant as: one whose origin or selection is due to the activities of mankind. Such plants may arise either by deliberate or chance hybridization or by further selection from existing cultivated stock or they may be selected from a wild population and maintained as an entity by continuous cultivation.
Frequently, domestication is regarded as just a special form of evolution as it happens unconsciously and the same mechanisms of selection are at work (Hanelt 1986; Van Raamsdonk 1993; Van Raamsdonk and van der Maesen 1996; Zohary 1984). Specialized terms (Table 1.1) are used to refer to cultivated plants that are important for effective communication and classification. A cultigen is defined as taxon with only cultivated representatives, such as Triticum aestivum L., the species name encompassing all hexaploid wheats. The term taxon for this definition is controversial, however, as we will discuss. This term is contrasted with an indigen, that is, a wild taxon in its natural habitat and distribution area, that is, a noncultivated plant. A culton is a systematic group of cultivated plants, and the ICNCP recognizes two types of culta: the cultivar and the cultivar-group. A cultivar is a nomenclatural term referring to the most basal taxonomic unit of cultivated plants. A cultivar-group refers to an assemblage of similar named cultivars. A landrace is a cultivar that originated as a product of (the first stages of) mass selection (and not as a product of modern plant breeding), mostly confined to a certain region. It also had been referred to as an indigenous cultivar or a primitive cultivar. Schwanitz (1967) outlined some special features of cultivated plants that can make for rapid divergence from their progenitors: (1) increase of number of desired plant parts; (2) increase of size of desired plant parts by allometric growth; (3) loss of undesired morphological or chemical traits; and (4) loss of defense mechanisms. All of these traits may arise rapidly, make the cultivated plant quite different from its progenitor(s), obscuring the connection between them. In addition, the study of relationships of crops to progenitors can be hindered by hybridization with weeds producing "crop-weed complexes."
1. PLANT NOMENCLATURE AND TAXONOMY
11
Crop-weed complexes have long been a subject of extensive systematic study and reviews (De Wet and Harlan 1975; Hanelt 1986; Harlan 1965, 1975; Pickersgill1971, 1981, 1986; Van Raamsdonk and Van der Maesen 1996). Most of these studies point out the complex interaction among weeds, domesticates, and their wild relatives. Extensive hybridization makes the classification of crop-weed complexes especially difficult. Pickersgill (1981, 1986) suggested that weedy progenitors evolve to cultivated plants, but cultivated plants can also evolve back to weeds. Modern cultivars are produced by extensive artificial hybridization, and pedigree records are often incomplete or unavailable for proprietary reasons. For example, separate modern cultivars of potato have in total incorporated germplasm from 16 wild species in the pedigrees (Ross 1986; Plaisted and Hoopes 1989). Despite these separate pedigrees, all are classified as the single species Solanum tuberosum 1. II. SPECIES CONCEPTS IN WILD PLANTS The discussion of species concepts has become a cottage industry. Not only does the number of pages and full-length books devoted to the topic continue to grow, but new concepts of species proliferate at an extraordinary rate.
Rieseberg and Burke (2001)
Species have a central place in taxonomy as they form the basic units of biological classification (Davis and Heywood 1963; Greuter et al. 2000), but there is no consensus on how to define species, and likely never will be. Why? New species concepts have changed considerably with the development of new data and theory, and are likely to continue to change. Each development has led to new species concepts, and Mayden (1997) lists a total of 22. Many concepts, however, are minor variations of others, and some are rarely applied. The following are six major classes of species concepts. A. Morphological Species Concepts
Morphological species concepts define species entirely on morphological or anatomical characters. Because of their utility, they are frequently applied, especially historically when taxonomists worked in large herbaria and the form of the plant was the major data set available. This can operate effectively by a method referred to as sheet shuffling, whereby a collection of herbarium specimens is initially sorted into species based on a subjective impression of overall form. This can be followed by
12
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
microscopic examination to gain additional data to modify species delimitation. Cronquist (1978) defined this practical application of the morphological species concept as the taxonomic morphological species concept: Species are the smallest groups that are consistently and persistently distinct, and distinguishable by ordinary means.
The characters leading to this subjective judgment are often unclear, sometimes even to the taxonomist applying them. Typically, characters of special value are weighted, for example more weight is given to reproductive than to vegetative characters. A potential problem with this is that because the methods of the taxonomist are not always evident, preference for one of several conflicting taxonomic treatments are often made based on a taxonomist's reputation, rather than on the inherent qualities of a classification. The advent of computers allowed the practical application of multivariate techniques to taxonomic data. In· practice, morphological, anatomical, chemical, or any character type was appropriate for analyses. The basic idea was that many characters were overlooked in defining species, and that species were best defined by an objective and equal treatment of all characters, reproductive and vegetative (Sneath and SokaI1962). An added claim was that these methods opened up these classifications to scrutiny, as data and analytical techniques were open for evaluation by all and not hidden and inscrutable impressions of experts. In practice, a taxonomist scores quantitative or qualitative characters and enters them on rectangular data matrices (data entry cells with characters versus individuals). Various algorithms then transform this matrix into a triangular similarity (or dissimilarity) matrix of individuals by individuals. Different individual data reduction techniques then convert a similarity matrix to a graphical display of phenetic trees (phenograms or dendrograms), ordination plots (as principal components analyses, principal coordinates analyses, or multidimensional scaling analyses). Decisions are made on species limits based on clustering of individuals, but there is no universally accepted objective criterion to determine the degree of clustering to define species or higher taxonomic levels. Sokal and Crovello (1970) defined this phenetic morphological species concept as "dense regions of hyperdimentional space" (referring to clustering of individuals in ordination analyses). This concept can provide misleading results of species boundaries in certain crops however where only a few genes have remarkable mor-
1. PLANT NOMENCLATURE AND TAXONOMY
13
phological effects as in the case of Brassica oleracea where the same species has been selected for forms as divergent as broccoli, brussels sprouts, cabbage, cauliflower, kale, and kohlrabi. B. Interbreeding Species Concepts
The interbreeding species concepts focus almost entirely on the ability of species to exchange genes naturally or artificially, as assessed by artificial crossing programs, studies of mechanisms to facilitate gene flow, and biological isolating mechanisms. Mayr (1942) advanced the biological species concept as "Species are groups of interbreeding natural populations that are reproductively isolated from other such groups." This concept matches that held in the minds of the general public and is intuitively appealing, but many practical and theoretical problems were raised. Procedurally, it is almost impossible to apply to a group of any size because replicated pair-wise crosses are needed in most interspecific combinations to be confidently interpreted (Sokal and Crovello 1970). As well, data from greenhouse situations are not always applicable to the field, and varying degrees of crossing success are not easily interpreted. Also, the concept is inapplicable to species reproducing apomictically. The lifetime of crossing studies by Rick (1963, 1979) in tomato is a notable application, but this depth of study is exceptional and rarely has been applied to other groups. Such crossing studies were common in the 1940s to 1960s and the term biosystematics originally referred to the use of breeding programs (by biosystematists) to infer evolutionary relationships among organisms. The term later became broadened to refer to a wide variety of experimental data gathering programs. Because of the broad definition of the term the need for this term has lessened (Stuessy 1990). The difficulty to define differing degrees of intercrossability led to qualifier terms. Harlan and de Wet (1963), working in grasses, recognized compilospecies as genetically aggressive, highly polymorphic species, often of complex hybrid origin, often containing more than one ploidy level, often very weedy, and obscuring other species boundaries. They suggested that such species were typical progenitors of crops. Grant (1981) referred to semispecies as populations of plants on the way to becoming species but yet without sufficient reproductive isolation, and used Lotsy's (1925) term synganleon to refer to a broadly sympatric set of semispecies. Some biosystematic terms were placed in a hierarchy of relationships (Clausen et al. 1945; Clausen 1951; Grant, 1981), from ecotype (lowest)
14
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
to ecospecies, cenospecies, and comparium. An ecotype consists of all members of a species that are fitted to survive in a particular environment, and different ecotypes within species have no interbreeding barriers. An ecospecies is an assemblage of ecotypes and are separated by incomplete sterility barriers. Cenospecies are assemblages of related ecospecies that when crossed produce highly to completely sterile hybrids. A comparium is a group of related cenospecies that cannot be crossed with one another. Patterson (1985) advanced a variant of the biological species concept termed the recognition species concept. Mayr's (1942) biological species concept suggested that biological isolating mechanisms were an accidental by-product of genetic reconstruction during speciation. Patterson, on the other hand, suggested that specific forces were responsible for such reconstruction, and viewed biological isolating mechanisms as an active, positive force in speciation. His concept stimulated the search for adaptations that assist the process of meiosis and fertilization, but he realized that isolation and recognition are just two components of the same process. C. Ecological Species Concepts
Van Valen (1976) was confounded by the perplexing array of variation in oaks. Oaks have broadly sympatric sets of very similar species, often hybridizing among each other, which he termed multispecies. These were similar to the compilospecies of Harlan and de Wet (1963, described earlier). He noted that despite many hybrids, species maintained their integrity in specific habitats. For example, Quercus bicolor Willd. (swamp white oak) was broadly sympatric with Quercus macrocarpa Michx. (burr oak) in the Great Lakes and Ohio River basins, and they frequently hybridized. The former, however, grew in wet bottomlands, streamsides and swamps, and the latter in mesic habitats of rich woods and fertile slopes. Van Valen stated, The control of evolution is largely by ecology and the constraints of individual development. He outlined the ecological species concept as: A species is a lineage (or a closely related set of lineages) which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from other lineages outside its range.
He contended that reproductive isolation of allopatric populations is of minor evolutionary importance, and that ecological factors are more closely related to genetic differences than reproductive isolation.
1. PLANT NOMENCLATURE AND TAXONOMY
15
D. Cladistic Species Concepts
The most recent, conceptually difficult, and terminology-laden set of species concepts are grouped here under cladistic species concepts. They arose out of the ideas of Hennig (1950, 1966) who used phylogenetic history as the sole criterion for grouping taxa, irrespective of morphology, interbreeding behavior, or ecological considerations, except as they may be used to help reconstruct phylogenetic history. He never used cladistics to help define species, but his concepts have been applied this way as will be discussed. Basic cladistic terms are briefly explained; the reader is directed to Wiley et al. (1991) for more detailed explanations. Cladistics refers both to a set of methods for inferring phylogeny and a philosophy of systematics in which only monophyletic groups are accepted. Not everyone who uses cladistic methods, however, accepts a cladistic philosophy of classification, and some do not consider cladistics to be appropriate to recognize species. A monophyletic group encompasses an ancestor and all of its descendants, as determined by a cladistic analysis that produces phylogenetic branching trees (cladogram). The basic procedure to construct cladograms is to try to begin with a putatively monophyletic group, referred to as an ingroup, such as "species A" or "tuber-bearing solanums," or "the sunflower family." Evolutionary relationships within the ingroup are determined by the use of an outgroup(s) that are analyzed for the same characters and are used to construct the tree. A sister group is the most closely related monophyletic outgroup to the ingroup, and further outgroups also can be used for a multiple outgroup analysis (Maddison et al. 1984). (See Fig. 1.1.) Characters are scored for all ingroup and outgroup taxa, just as in phenetic studies. Any character type can potentially be used, including
Sister group Second outgroup ~ E
Fig. 1.1.
Ingroup
~
Terms relative to cladograms.
D
cl
16
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
morphological or molecular characters (as DNA base pairs or restriction endonuclease sites). Most analyses score these characters qualitatively, as presence or absence (0-1), or as a range of discrete character states (0-1-2-n). Great care is taken to score only homologous characters arising from common ancestry, avoiding characters that may look similar but actually arise in parallel from different ancestors. Orthologous characters are homologous by a speciation event, meaning that they trace their ancestry to a common progenitor, and are taken as the only useful type of homologous character. Molecular taxonomists are searching for single-copy nuclear genes for phylogeny construction, and doing everything possible to avoid paralogous characters that have arisen from gene duplication. Such duplicated genes can evolve separately in the same lineage, may falsely appear to be homologous, but can provide misleading phylogenetic information. Cladograms are then constructed from these data by various methods, but a common method is to use the parsimony criterion, that invokes the minimum number of evolutionary changes to construct the tree. Other techniques also are used, such as maximum likelihood (Felsenstein 1981; Swofford et al. 1996) that searches for trees that may be longer but that represent character changes based on certain evolutionary models. The tree is rooted based on characters of the outgroup(s), and in this method monophyletic groups are supported only by synapomorphies (shared derived characters) relative to the plesiomorphies (ancestral or primitive characters) of the outgroup(s). Cladograms may look like phenetic trees (dendrograms), but phenetic analyses are based on overall similarity and dendrograms are constructed by an average of all characters, not individual characters on each branch as in cladograms. Pheneticists infer only overall similarity of organisms from their phenograms, not phylogeny, and most cladists interpret cladograms phylogenetically. Monophyletic groups are then determined from the cladogram that trace to a single internode (all of which are supported by synapomorphies). Cladists avoid recognizing all nonmonophyletic groups, includingparaphyletic groups (groups containing some, but not all descendants of the most recent common ancestor), and polyphyletic groups (groups where the common ancestor is placed in another taxon). Paraphyletic species have been recognized, however, as described in Figure 1.2. There is a wide diversity of opinion on application and interpretation of these concepts, providing further problems. For example, phylogenetic results of the same organisms obtained from different data sources are frequently in conflict (Wendel and Doyle 1998). Some advocate analyzing data separately to discover datasets providing misleading results,
17
1. PLANT NOMENCLATURE AND TAXONOMY
Monophyletic
Paraphyletic
Fig. 1.2.
Polyphyletic
Cladistic relationships relative to cladograrns.
while others advocate combining all data into a single matrix for a total evidence analysis (e.g., Eernisse and Kluge 1993). Cladistic results also can be affected by poor choice of outgroups, by analysis of unrecognized nonorthologous characters, by different choice of cladistic algorithms to construct trees, by insufficient ingroup or outgroup sampling, and by different methods to handle missing data. There is also debate among cladists whether cladograms truly reflect recency of common ancestry (process cladists), or whether they need to be theory neutral and only show patterns decoupled from assumptions of ancestry (pattern cladists or transformed cladists) (Ereshefsky 2001). Perhaps the greatest source of debate is the use of cladistics at all at the species level. This is because cladistic procedures assume divergent taxa, yet individuals within species often (generally) hybridize, leading some to consider cladistics to be an inappropriate method to define species (Templeton 1989). Another complication is the differences in opinion in cladistic species concepts. The most strict interpretation of the cladistic species concept was advanced by the process cladists Mishler and Brandon (1987) as the autapomorphic species concept: A species is the least inclusive taxon recognized in a classification, into which organisms are grouped because of evidence of monophyly ... that is ranked as a species because it is the smallest "important" lineage deemed worthy of formal recognition.
18
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
Outgroup
T1
Plesiospecies AIA2A3A4AS A6 A 7
Apospecies B 1 B 2 B 3 B 4 Bs
--::--------;---:--~:---;----=---:-------~:----=---=----:--~
Fig. 1.3. Apospecies and plesiospecies as depicted by Olmstead (1995). Under this evolutionary model, a set of populations is shown at initial time To when a speciation event occurs, as depicted by the thick horizontal line designating a synapomorphy forming the species. At initial time To, the new apospecies leaves a remnant set of populations that are now paraphyletic (plesiospecies). Later (at time T 1 ) extinction of populations leads to monophyly of both species. Bold lines designate populations surviving to time T 1 • This shows the theoretical need to withdraw the strict criterion for monophyly in cladistic species concepts.
The criterion for "important lineage" necessary to define a species can vary from ecological, reproductive, or developmental criteria. Recently, Rieseberg and Brouillet (1994) and Olmstead (1995) have argued that geographically localized models of speciation typically produce a monophyletic daughter species and remnant paraphyletic progenitor species, and argue that a strict concept for monophyly fails for many species. Olmstead (1995) termed the former apospecies and the latter plesiospecies. He traced a hypothetical set of populations over time To (initial species divergence) and T 1 (later time with full development of apospecies) that showed the necessity of recognition of paraphyletic species if apospecies are to be recognized at all (Fig. 1.3). Cracraft (1989) has a tendency to lean in the direction of pattern cladistics and advanced the phylogenetic species concept as: A species is an irreducible (basal) cluster of organisms, diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent.
1. PLANT NOMENCLATURE AND TAXONOMY
19
This definition emphasizes smallest diagnosable units by a practical set of diagnostic characters, as discovered by cladistic procedures, but makes no inference that these are monophyletic. E. Eclectic Species Concepts
The former species concepts highlight single processes as definitive for species. Eclectic species concepts, in contrast, take a pluralistic view that species are formed and maintained by a variety of criteria. For example, Doyden and Slobobchikoff (1974) constructed a flow chart detailing a variety of morphological, geographical, biological, and ecological criteria to define species. Mayr (1982) modified his biological species concept to include an ecological component: A species is a reproductive community of populations that occupies a specific niche in nature. Stuessy (1990) concluded his discussion of species concepts with a basic agreement with Crum (1985): Although subjectivity is involved with decision making, a species is only as good as the knowledge and insights used in its delimitation. Certain methodologies help. So do good sense and good judgment based on meaningful experiences, and the more the better.
Templeton (1989) outlined the cohesion species concept as: The most inclusive group of organisms having the potential for phenotypic cohesion through intrinsic cohesion mechanisms through genetic and or demographic exchangeability.
He attempted to define specific mechanisms that drive the evolutionary process to speciation. He considered that his concept attempts to utilize the strengths of [biological, evolutionary, and recognition species concepts] while avoiding their weaknesses with respect to the goal of defining species in a way that is compatible with a mechanistic population genetics framework.
Ereshefsky (2000) outlined several classes of species concepts, and advanced a pluralist species view that no single correct definition of species exists and that a number of alternative concepts may be legitimate. F. Nominalistic Species Concepts
Some question the very existence of species, and believe that individuals or interbreeding populations are the only population system with any
20
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
objective reality. This concept arose out of the philosophy of nominalism, arguing that only individuals are real and that classes of any kind (as species, genera, or families) are artificial constructs. For example, Burma (1954) stated: species are highly abstract fictions. Levin (2000) likewise argued that only the local population is the unit of evolution, and species are artificial. Some evidence supported nominalistic concepts. Ehrlich and Raven (1969) documented many cases of reduced gene flow in both plants and animals that would preclude any cohesive force to maintain species. They contended: Selection alone is both the primary cohesive and disruptive force in evolution ... for sexual organisms it is the local interbreeding population and not the species that is clearly the evolutionary unit of importance.
Rieseberg and Burke (2001) countered this view, arguing that prior studies grossly underestimated levels of gene flow, and that only very low rates of gene flow are actually needed for the diffusion of strongly advantageous alleles needed to maintain species integrity. III. CLASSIFICATION PHILOSOPHIES IN WILD AND CULTIVATED PLANTS
A. Wild Plants The previous section reviewed a variety of types of data and analytical and philosophical methods used to define species, and similar criteria are used to group species into higher ranks (as genera, families, and orders). The early classifications were based on intuitive interpretations of morphological data, and in many cases, they defined groups that have continued to be maintained. For example, the grass family, sunflower family, and many other traditional taxa are clearly natural as determined by molecular data. The intuitive, interbreeding, phenetic, cladistic, and eclectic classification philosophies mentioned in the previous section for species also are used to group species within genera, and all but the interbreeding classification philosophies have been used to classify above the genus level (reviewed in Stuessy 1990; Judd et al. 1999). Many botanists today examine cladistic relationships, but major disagreement rests on how to translate cladistic results into a classification. Some argue (e.g., Stuessy 1990), that cladistic data are only one component of phylogenetic relationships, other components being chronistic (time of divergence of
21
1. PLANT NOMENCLATURE AND TAXONOMY
clades), patristic (amount of character divergence within lineages), and phenetic (overall similarity). There are no algorithms to incorporate all of these data types into a classification, however, unlike classifications based on phenetics or cladistics, and intuitive judgments are still used by many to construct these eclectic classifications. B. Cultivated Plants The inconsistencies and lack of agreement of taxonomists dealing with the same materials are remarkable, to say the least, and are even more striking when the treatment of differing crops are compared.
Harlan and de Wet (1971)
The major goals of taxonomy reviewed suggest that for agronomists and horticulturists, stability and predictivity would be very important. The philosophies and practices to define wild species and to group them into genera and higher-level ranks are wide and diverse. The question remains-what would happen if different taxonomists were to work on the same group of plants and produced different classifications? Would one be "better," and by what criteria could we judge one classification to be "better"? These questions can be explored by comparing such different classifications, and we give examples from tomato, potato, Brassica, lettuce, Prunus, and wheat. One of the major reasons for discrepancies among taxonomic treatments is that the taxonomy of plants is often complicated by the occurrence of outcrossing, selfing, apomixis, clonal propagation, or polyploidization, producing different variation patterns that can be difficult to subdivide into easily recognizable units. The taxonomy of cultivated plants has the extra complication of the influence of the domestication process on variation patterns, with domestication having major and rapid effects on morphological characters used for classifications. 1. Tomato. Spooner, Anderson, and Jansen (1993) examined outgroup relationships of tomato (many recognize as the genus Lycopersicon Mill.) to potato and other members of the Solanaceae L. (Fig. 1.4). The results convincingly showed tomato to be firmly internested in the genus Solanum L. Based on these results, Spooner et al. (1993) followed a cladistic classification to assign tomato to the genus Solanum, matching the original treatment of Linnaeus (1753), and a minority of other taxonomists who foresaw this generic relationship based on morphological data. Subsequent molecular studies unequivocally supported the cladistic placement of tomato in Solanum (Olmstead and Palmer 1992,1997;
22
D. SPOONER, W. HETTERSCHEID, R, VAN DEN BERG, AND W. BRANDENBURG
, - - - - - - - - Capsicum
Outgroups . . . . - - - - - - - - - Datura ] Cyphomandra (now Solanum) Solanum pseudocapsicum
'--__...;----- s. quitoense
j Other Solanum
' - - - - - - - S. macrocarpon L-
S. nigrum
Lycopersicon esculentum ]
L. chmielewskii
Tomato
L. peruvianum S.lycopersicoides ] Tomato outgroups in S. sitiens sect. Lycopersicoides S. ochranthum and sect. Juglandifolium S. agrimonifolium ] S. phureja S. verrucosum
Potato
S. albornozii
S. bulbocastanum
S. brevidens
]
S. etuberosum
Solanum sect. Etuberosum
S. fernandezianum
S. suaveolens ] S. muricatum L.-
S. taeniotrichum
Solanum sect. Basarthrum
S. appendiculatum ] , . . - - - - - S. dulcamara Other Solanum LS. jasminoides
Fig. 1.4. One of two-most parsimonious cladograms (as a phylogram) of chloroplast DNA restriction site data examining wild tomatoes (here labeled Lycopersicon), their sister groups (Solanum sect. Lycopersicoides, sect. juglandifolium) , wild potatoes (Solanum sect. Petota), and further outgroups in Solanum sect. Etuberosum, sect. Basarthrum, and other Solanum (modified from Spooner et al., 1993).
Bohs and Olmstead 1997, 1999; Peralta and Spooner 2001). These unequivocal cladistic results are stimulating many taxonomists to place tomato in Solanum, but many agronomists and horticulturists have not accepted the name (but see Van der Heuvel et al. 2001). Most users of Lycopersicon clearly base their reluctance entirely on a desire to maintain nomenclatural stability rather than adherence to any particular classification philosophy. Ingroup relationships within tomato have varied greatly. Muller (1940), Luckwill (1943), and Child (1990) treated tomato based on tax-
23
1. PLANT NOMENCLATURE AND TAXONOMY
Luckwill (1943)
Rick (1919)
Child (1990)
GBSSI sequence
Subgenus Eulycopersicon Esculentum complex Series Lycopersicon Group 1 L. esculentum (8) L. esculentum (2) S. lycopersicum S. lycopersicum L. pimpine11ifolium - - - L. pimpinellifolium - - - S o pimpinellifolium--- S. pimpine11ifolium L. cheesmaniae S. cheesmaniae S. cheesmaniae L. pennellii ~ Series Neolycopersicon Group 2 L. hirsutum -~ ' - - - - S. pennel1ii S. chmielewskii L. chmielewskii "-.\_ Series Eriopersicon S. perovianum N L. parvinor~m ~ S. habrochaites S. neorickii Subgenus Eriopersicon Peruvianum complex S. chmielewskii Group 3 L. perovianum (5)~-4+- L. chiJense S. chilense S. pennel1ii L. pissisi- ? L. perovianum S. peroVianum S. habrochaites L. cheesmaniae (2) S. neorickii S. neorickii S. chilense L. hirsutum (2) S. perovianum S L. glandulosum
Fig. 1.5. A comparison of taxonomic treatments of wild tomatoes from Luckwill (1943; a taxonomic morphological species concept), Rick et al. (1979; a biological species concept), Child (1990; taxonomic morphological species concept), and a possible cladistic interpretation of a GBSSI DNA sequence cladogram of Perlata and Spooner (2001; Fig. 1.6).
onomic morphological species concepts. The treatments of Rick (1963, 1979) and Rick, Laterrot, and Philouze (1990) grouped the species completely differently based on interbreeding concepts (Fig. 1.5). Peralta and Spooner (2001) produced a phylogeny of tomato based on DNA sequences of the single-copy GBSSI (waxy) gene (Fig. 1.6 on page 24). It could be interpreted to distinguish three groups. One of the species, the highly polymorphic Solanum (Lycopersicon) peruvianum 1. would be placed into two groups, one consisting of populations from northern Peru, and another of populations from central to southern Peru (Fig. 1.5). A phenetic morphological study by Peralta and Spooner (in press) supported all species, including a north and south Solanum peruvianum species. A taxonomic monograph of tomato is in preparation by Iris Peralta, Sandra Knapp, and David Spooner. 2. Potato. Ingroup relationships within potato have differed even more than within tomato. Harlan and de Wet (1971) advanced the gene pool concept (a variant on the biological species concept) based on their frustration with traditional taxonomy to provide consistent answers to relationships of crops and their wild relatives. They initially tried to use taxonomic treatments of crops to give insight into materials to use in their breeding programs. They noted, however, such great discordance between taxonomic treatments of potato, maize, wheat, and sorghum that they rejected traditional treatments and constructed the gene pool classification. They compared the taxonomic treatments of potato of
24
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG
Solanum lycopersicum Solanum pimpinellifolium Solanum cheesmaniae 70(3) ......---- Solanum peruvianum north 1 - - - - - Solanum chmiewelskii 100 Solanum neorickii Ingroup 1 - - - - - Solanum peruvianum south 1 - - - - - - Solanum chilense \ - - - - - Solanum habrochaites Solanum pennellii 64(2) 100 Solanum j uglandifolium Solanum ochranthum 100 Solanum lycopersicoides 86 (3) Solanum sitiens L..--~":"'Solanum tuberosum Outgroup 97 Solanum bulbocastanum Solanum jamesii 100 Solanum etuberosum Solanum palustre Solanum muricatum 24 (l)
...----+--
L--
L..--
1--
Fig. 1.6. Abstracted results ofa GBSSI (waxy) gene phylogeny of wild tomatoes and outgroups (Peralta and Spooner 2001).
Bukasov (1933) and Bukasov and Kameraz (1959) to Hawkes (1963), and noted that Hawkes (1963) recognized about one-half as many species, and grouped these species very differently into series. Their classification starts from the crop itself. Crossability is represented in a graph with three genepools, with the primary genepool 1 being the crop and wild species easily crossable to it, and the second and third being the rest of the plant kingdom, according to degree of crossability to the crop (genepool 2 crossable with some difficulty, genepool 3 crossable with great difficulty). Genepool1 is based on the biological species concept and is then to be subdivided in two subspecies, one with spontaneous populations, the other containing the cultivated "races" (their "race" not being equivalent with cultivar of cultivated plant classification). This system is a very special purpose classification and not an alternative to any form of taxonomy in general. Why? Every primary genepool chosen results in a separate classification based entirely on the choice of each crop used for comparison. This could lead to as many dif-
1. PLANT NOMENCLATURE AND TAXONOMY
25
ferent classifications of plants as there are primary genepools for comparison. This is unacceptable, since genepools 2 and 3 contain close and less close relatives of the primary genepool "species" and do in fact thus represent the entire rest of plant kingdom (genepool 41). The relationships of the genepools with the rest of the plant kingdom remain unresolved. Another objection is that the category of subspecies is misused for convenience to contain either wild plants or cultivated material. This last option creates an unfortunate hybrid between the taxonomy of wild plants (the category itself) and of cultivated plants (the actual content of the category). Similar problems exist in the biological species concept. The system proposed by Harlan and De Wet has already led to many "infraspecific" classifications of crops, using Latin binomials for cultivated plant groups that as we argue should be avoided. Spooner and van den Berg (1992) followed up on the Harlan and de Wet (1971) comparison of potato with an examination of later taxonomic treatments of Bukasov (1978) and Hawkes (1990), and added Correll (1962) and Gorbatenko (1989) (Fig. 1.7). All four of these authors apparently applied a taxonomic morphological species concept, but Hawkes (1990) also took intercrossability data into account. The treatments differ in the number of series recognized, the number of species in each series, and the different affiliation of species to these series. Likewise, Spooner and van den Berg (1992) also compared the nearsimultaneous independent publication of the potatoes of Bolivia by Hawkes and Hjerting (1989) and Ochoa (1990). Their treatments differed in the number of species recognized, their affiliation to series, the taxonomic rank used to recognize divisions of species (botanical varieties or subspecies), and in their hypotheses on which of these species are of hybrid origin and whether they form introgressant populations with other species. 3. Lettuce. The influence of domestication on taxonomic classification is shown very clearly in cases where through the domestication process the morphology of the plants are changed, and species are described based on these morphological characters. In the case of lettuce, the obvious differences between cultivated and wild material led to the distinction of the species Lactuca sativa 1. as separate from its presumed wild ancestor L. serriola 1. Cultivated material lacks the prickles on the midrib of the lower side of the leaves, and shows prominent heads. De Vries and van Raamsdonk (1994) reiterated this separation in a numerical morphological analysis. However, it is highly questionable whether botanical species should be recognized using characters that are clearly the results of human selection. An alternative classification would be to consider wild and
26
D. SPOONER, W. HETTERSCHEID, R. VAN DEN BERG, AND W. BRANDENBURG Correll 1962 Bukasov 1978
]uglandifolia (Rydb.) H.wk.. 1944 MoreUiformia H.wk., 1956 Bulbocastana (Rydb.) H.wk.~ 1'/44 Pinnatisecta (RyJb.) H.wk.. 1944 Trifida Correll 1950 Cardiophylla Bul< .. CA,....1I1952 Polyadenia Buk.exCorre1l1952
Hawkes 1990
Gorbatenko 1989
(Sr ----------------
------------I---------___{S
4r ---------------- ------------~---------------------___{4) 1 1). - - - - - - - - - - - + - - - - - - - - - - { 1 )
- - - - - - - - - - - +-.,.----------( 2) 1
1)-
8
S}
-----------I-.J -----------~~------------------~1~
-----------I-.J
2 111
3 2
-----------1----1 -----------+----------+(2 1
Glabrescentia lluk';:'~: &
Kame...,
Circaeifolia H.wke, 1954 Lignicaulia H.wk.. 1989 Olmosiana Och,,, 1%5 Yungasensa C,..,dll%l Tarijensa C,,,dI1962 Berrhaultiana Buk,.,..." nuJ
et
'---------111\-1--"------------'
U1
PDV
PNRSV
ACLSV
MS
Day of thermoLS therapy
-
20
20
No. of No. of prepared surviving meristems meristems MS
LS
15
3
5
+
-
+
28
20
22
19
-
+
+
40
46
20
14
Cafona
+
+/-
Dr. Mascle
+
-
Hauszwetschge Hungarian Best Koroszer Weichsel
-
20
Virus-free lines after thermoptherapy PPV
MS
LS
MS
LS
1
1
1/1
1/1
3
-
-
-
9
8
4/4
+/-
28
13
21
14
8
4
5
-
+
40
85
20
10
23
-
4
-
+
-
16
39
21
1
9
1
6
-
++
-
-
12
20
19
0
11
0
5
-
36
27
18
6
4
5
1
-
30
13
20
9
11
2
4
++
-
Kozlienka
-
++
Kraska
+
-
+/-
Marille Viessling
+
-
-
-
San Castrese
+
-
Spatbluhende Koch
+
-
32
20
19
16
12
27
-
32
30
-
20
20
9
47 4
1
-
1
1/1
15
-
54
-
4
27
12
3
7
1
5/5
MS
MS
4/4
5/5
MS
-
2/3
9/9
8/8
9/9
8/8
-
-
4/4
5/5
-
3/4
-
5/5 8/8 1/1
1/1
-
ACLSV
LS
1/1
6/6
2/2
4/4
-
8/8
5/5
4/4
717
LS
3/3
3/4
8
PNSRV
PDV
1/1
LS
216
M. LAIMER
rates in elimination of pathogens show high variation and depend on plant species, pathogen, and the type of infection (single or mixed) under investigation. By comparing titers of ACLSV, ASGV, and PPV in leaves of single in vitro shoots of different apple and apricot cultivars before and after variable periods of thermotherapy followed by meristem preparation there are several noteworthy observations: 1. virus particles persist and replicate over the entire shoots during thermotherapy since they can be detected by ELISA even after three weeks of heat treatment; 2. there is a distinct difference in the success rate depending on the duration of the heat treatment, that is, the longer, the better, provided the plant genotype allows it; 3. since heat treatment was adapted to the physiological state of the plant material, this difference is logically due to genotypic variation among the cultivars; 4. mixed infections are more difficult to eliminate, confirming that double infections may cause greater than additive effects; S. the time frame required for reliable testing for the absence of eliminated viruses can be reduced by at least six months by using PCR instead of ELISA detection. The elimination of the filamentous viruses ACLSV, ASGV, and ASPV from apple cultures yielded quite different results among cultivars, indicating again the specificity of the host-pathogen interactions. ACLSV is present in 28 accessions in Malus and Prunus of the Vienna Collection (www.boku.ac.at/iam/pbiotech/phytopath/col.html#aclsv). Of these in vitro cultures were established and 12 accessions of Malus were subjected to various therapy procedures, four cultivars containing ACLSV as single infection and eight cultivars containing ACLSV in a mixed infection. When present as a single pathogen, ACLSV was easily eliminated, but slightly more resistant to elimination treatments, when present in mixed infections (Table 4.4). The distribution pattern of ACLSV further explains the ease by which this virus is eliminated through meristem preparation (Knapp et al. 1995a). ACLSV accumulates in stems of tissue cultures in a typical pattern, that is, in decreasing concentrations toward the apex. In stems of main shoots, it appears more frequently than in sterns of newly formed axillary shoots. ASPV was present in the VC (www.boku.ac.at/iam/pbiotech/phytopath/col.html#aspv) in 17 accessions in vitro, but only twice as a single infection. These were obtained after thermotherapy treatment of
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
217
multiple infections, where it had persisted, or as defined single infections kindly provided by J. Kummert (Gembloux). With eight of these cultures (two single, six mixed infections) thermotherapy experiments were conducted, and ASPV was easily eliminated (Table 4.3). ASGV was the most recalcitrant pathogen to eliminate from Malus cultures in the whole program. It was present in the VC in seventeen accessions, eight as mixed infections together with ACLSV and ASPV and nine as single infections as the remaining virus from previous elimination experiments (www.boku.ac.at/iam/pbiotech/phytopath/col.html #asgv). From a pomological point of view, this plant material should not be included in further propagation schemes. However, for improving our understanding of viruses, we considered these accessions valuable tools for elimination studies. Eight of these cultures (four mixed, four single infections) were submitted to thermotherapy treatment and meristem preparation (Table 4.3,4.5). The percent of shoots freed from ASGV was rather low. Heat apparently did not effectively inhibit ASGV replication and distribution throughout the plant. Even explants from growth during the last week of the treatment were not free of the virus. It is still unclear how ASGV migrates into the shoot apex, possibly through meristematic cells in the cambium in dividing zones. It appears noteworthy, however, that meristems of lateral shoots often yielded shoots free of ASGV. These axillary shoots were formed only during the first week of the heat treatment or
Table 4.5. Elimination results of viruses from tissue cultures with single and mixed infections. Infection status
Apple cultivars
Single ACLSV
Arlet Elstar Kronprinz Landsberger Reinette
ACLSV mixed with ASPV
ACLSV mixed with ASGV and ASPV
Observations ACLSV is eliminated easily
Fuji Jonagold Jonagored Maschanzker
ACLSV is eliminated easily
Champagner Reinette Gelber Bellefleur Rubinette Summerred
ASPV sometimes persists ASGV is hardly eliminated
ASPV sometimes persists
ACLSV is eliminated easily
218
M. LAIMER
during the week of temperature adaptation. In fact, most of the ASGVfree meristems originated from lateral shoots obtained during the one week of stepwise temperature adaptation. The isometric viruses of the Ilarvirus genus are readily detected by the available protocols and easily eliminated for stone fruit plants by the described procedures. ApMV as single infection in Malus tissue cultures was lost over the years in all plantlets indicating that the virus is not very stable. In stone fruits virus elimination studies of single infections of PNRSV and PDV were conducted at the lAM with Prunus instititia and Prunus cerasus, respectively. The limiting factor, however, in virus therapy for stone fruits appears to be related to survival after thermotherapy due to the sensitive reaction of the plantlets exposed to higher temperatures (Table 4.4). When the physiological growth characteristics of apricot are considered (Costes et al. 1995), the results obtained are not surprising (Table 4.4), namely that in most cases the meristems of lateral shoots grow better and yield a higher percentage of virus-free plants than meristems from the main shoots exposed to heat therapy. PNRSV is present in the VC in fifteen accessions in vitro (ten single, five mixed infections) from different origins throughout Europe. Infected Prunus insititia Kozlienka was used as positive control and as model for PNRSV elimination. PNRSV was easily eliminated by the described approach both from single and mixed infections. PDV is present in the Vienna Collection in eight accessions, four of which were established in vitro (www.boku.ac.at/iam/pbiotech/ phytopath/col.html#pdv). Of the three single infections (one was mixed with ACLSV and PNRSV) the Prunus cerasus cultivar Koroszer Weichsel has been our model to study the behavior of the virus in elimination treatments, which yielded convincing success rates (Table 4.4). V. ELIMINATION OF PHYTOPLASMAS
So far, the successful elimination of PD and other phytoplasmas has involved the use of tetracycline or heat (Nyland 1975; Davies and Clark 1994). Routine elimination ofphytoplasmas at the lAM, involves a combination of heat therapy and meristem culture, omitting the tetracycline treatment. AP-, ESFY-, and PD-infected in vitro cultures of the VC were initially used for the improvement of the detection system. AP is present in the VC as in vitro cultures in four accessions from different origins (www.boku.ac.at/iam/pbiotech/phytopath/col.html#ap). even though AP-infected plants often have strongly reduced growth habit. Thermotherapy and meristem preparation efficiently eliminate
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
219
Table 4.6. Elimination results of phytoplasmas from tissue cultures of apple, pears, and Prunus. No. of prepared meristems
No. of surviving meristems
Phytoplasma-free lines after thermotherapy
Species
Pathogen
MS
LS
MS
LS
MS
LS
Pyrus Prunus Malus
PD ESFY AP
49 21 22 53
19 5 18
46 20 14 21
10 3 9 3
45 19 13 21
10 3 9 3
7
AP, PD, and ESFY. Of the 21 main shoot meristems infected with AP, all were cured (Table 4.6). PD is present in the VC in four accessions, two of which have been established in vitro (http://www.boku.ac.at/iam/pbiotech/phytopath/ col.html#pd). Thermotherapy and meristem preparation were carried out, meristems were regrown to plantlets, and the expected success rate of elimination was confirmed, for example, from 46 main shoot meristems from pear infected with PD, 45 were free from phytoplasma, while all 10 meristems from lateral shoots were cured (Table 4.6). ESFY is present in the VC in twelve accessions, nine of which have been established in vitro (www.boku.ac.at/iam/pbiotech/phytopath/ col.html#esfy). Of fourteen main shoot meristems of Prunus thirteen were ESFY-free, while again all nine meristems from lateral shoots were pathogen-free (Table 4.6). VI. INDEXING, MASS PROPAGATION, AND GERMPLASM CONSERVATION Plantlets obtained from meristem tip culture are propagated in vitro as mericlones (Boxus and Druart 1986). As soon as possible, plantlets from each mericlone are individually indexed. These tests are repeated several times before deciding if a mericlone is virus-free. Indexing can be done by the use of indicator plants, ELISA, or PCR tests. The major advantage of PCR tests over ELISA testing is the considerable gain of time considering that evaluations by ELISA might take one and a half to two years until the initially reduced virus titer reaches a reliable detection level again. By applying PCR, test results concerning the health status of a culture can be obtained within six months after heat treatment and meristem preparation.
220
M. LAIMER
Virus-free clones are propagated by axillary branching for delivery to nurserymen (Boxus and Druart 1986; Rosati and de Paoli 1992). According to international regulations, virus-free elite plants are to be kept under conditions to avoid re-infection by air and soilborne vectors, for example, in an insect-proof screenhouse. As a result ofthe sanitation program that includes in vitro therapy and disease indexing, a number of virus-tested pome and stone fruit trees (cultivars and rootstocks) have been obtained. They are maintained in an insect-proof screenhouse at the lAM (Tables 4.7, 4.8). Currently, protocols for cryopreservation are being adapted to allow a long term storage of this valuable plant material.
Table 4.7.
List of virus tested apple trees at the lAM.
Apples Arlet Baumann Reinette Champagner Reinette Delbard Estival Elstar Fuji Gala Royal Gelber Bellefleur Golden Delicious Grosser Bohnapfel Ilzer Rosenapfel Jonagold Jonagored Jonathan Jonica Kronprinz Rudolf Landsberger Renette Lord Lambourne McIntosh Roter Boskoop Roter Trierscher Weinapfel Rubinette Steirischer Maschanzker Summerred Welschbrunner Rootstocks M7 M9 M25 M26 M27 MMlll
In vitro + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
In vivo + + + + + + + + + + + + + + + + + + + + + + +
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS Table 4.8.
221
List of virus tested stone fruit trees at the lAM.
Stone fruits Plum Bluefree Brompton Biihlers Friihzwetschke Cacaks Friihe (Rana) Cacaks Beste (Najbolja) Hanita Hauszwetschke Italienische Zwetschke President Stanley Valor Apricot Bergeron Harcot Luizet Orangered Priana Rouge de Sernhac Peach Dixired Red Haven Cherry Bigarreau Burlat Bigarreau Moreau Kor6szer Weichsel Ozark Premier Sunburst Van Rootstocks F12/1
GF8-1 Myrobolan B Prunus serotina ssp. capuli Prunus insititia Kozlienka
In vitro
In vivo
+ + + + + + + + + + +
+
+ + + + + +
+ + + + +
+ +
+ +
+ + + + +
+ + + +
+
+ + +
+ + + + +
+ + + + +
VII. CONCLUSIONS
This review summarizes 15 years experience of the Plant Biotechnology Unit of the lAM in the field of pome and stone fruit tree virus and phytoplasma elimination by tissue culture techniques. vVe have found that the most effective method for the elimination of viruses from a propagation chain of vegetatively propagated plant material is a combination of thermotherapy followed by shoot tip culture (Walkey 1991).
222
M. LAIMER
As has been stated (Mink et al. 1998), the in vitro system is most convenient for large scale virus elimination, multiplication of virusfree shoots, and the collection of virus-free germplasm. Similar as with in vivo thermotherapy, but even in shorter time frames, it is possible by repeated screening of progenies within the first six months to recover virus-free plants, which then can be rapidly propagated for further use, even if only a reduced number of meristems survive all handling steps. Little is known of the behavior of fruit tree viruses in in vitro systems. Factors such as random selection of healthy buds as starting explants, especially with unequally distributed viruses like PPV (Marenaud and Massonie 1977; Casper and Meyer 1981) and ACLSV (Gilmer et al. 1971; Fridlund 1973, 1983) have to be taken in account. Nevertheless, experience with over 50 fruit tree cultivars showed that random negative selection is a very rare event. It has been reported that distribution of virus infection decreases with time within a cultivar collection (Spiegel et al. 1996). However, this behavior, being dependent on the cultivar and the pathogen, is not a general rule. In the case of 'Champagner Renette' apple, for example, after four years of cultivation neither ASGV nor ACLSV were spontaneously eliminated in any of the shoots. In contrast, ApMV spreads very slowly, if at all, in orchards (Dhingra 1972) and is known to have rather unstable particles (Fulton 1972). Therefore, its rare occurrence and its loss in vitro is not surprising. Verification of the virus-free status of plants after thermotherapy procedures is only achievable through a careful screening procedure. Elimination methods like thermotherapy and meristem preparation may reduce the virus concentrations to levels where normal detection methods become too insensitive. Improved diagnostic tools can considerably enhance progress in this respect. The reliable detection of viral pathogens in fruit trees is an essential requirement for any sanitation program. Two-Step and DAS-ELISA with polyclonal antisera are the most important procedures for large-scale routine diagnosis and detection of many virus isolates, as they are available commercially. Immuno-tissue printing is more reliable than ELISA for the diagnosis of ASGV. Because of the extremely localized and limited occurrence of ASGV in stem tissues, ELISA might provide false negatives. The described localization of ASGV in young primordial leaves demonstrates that meristem dissection has to be carried out with high precision, as leaf primordia must not be included in the explant for effective elimination of this virus.
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
223
From our experience different criteria need to be applied to determine the best virus testing approach. If a certain plant material (be it in vivo or in vitro) is to be tested for the presence of one or only a few viruses or phytoplasmas (and antisera are available), IC-PCR is the method of choice since it combines the rapid extraction advantages of serology with the sensitivity of PCR detection. However, if the target is to verify the presence of a higher number of pathogens, a purification procedure of nucleic acids offers the advantage that only one sampling step of plant material is required, since it yields sufficient material to carry out and repeat several tests. We compared different RNA and DNA purification protocols and found the method of Bertheau et al. (1998 and of Kobayashi et al. 1998), involving the use of silica gel for a rapid purification of nucleic acids, to be the most appropriate technique, for the detection of viruses and phytoplasmas (Heinrich et al. 2001). Results from the virus elimination experiments with single and mixed infections of ASGV and/or ACLSV within in vitro shoots mimic experiences with these viruses under field conditions in the summer (Fuchs 1980), where at higher temperatures symptoms are masked, both visually and serologically. ACLSV is more strongly affected by elevated temperatures than ASGV (Welsh and Nyland 1965; Campbell 1968). ASGV is well known for its stability under higher temperatures (Lister 1970b). This property and its ability to accumulate in shoot tip regions may very well explain its recalcitrance to heat therapy. It is apparent that most of the serious virus disease problems around the world are the direct or indirect result of human activity (Thresh 1982) and that no technological developments in the field may be as efficient as an intelligent avoidance strategy. Production and distribution of virus free or virus-tested planting material of fruit trees is a technical challenge, but it also has political and socioeconomic implications. Just consider how often material of a chosen cultivar, once it is produced by one or another technique, is classified by the growers to be out-of-date. Few consider how long it takes to breed a new cultivar and how much time is required to make new accessions virus-free. The use of virus-and phytoplasma-tested planting material continues to be of major importance, if production of fruits should be accomplished in a sustainable way (Engel 1990). Virus and phytoplasma elimination in pome and stone fruit trees is a complex art, requiring elaborate techniques and skills and plenty of practical handling experience. Despite the considerable progress made in the last years, there is still great need to improve our knowledge of the process.
224
M. LAIMER
LITERATURE CITED Adams, A. N. 1978. The detection of plum pox virus in Prunus species by enzyme-linked immunosorbent assay (ELISA). Ann. Appl. BioI. 90:215-221. Adams, A. N., D. J. Barbara, and M. F. Clark. 1983. An indirect ELISA using a single antiserum and a general purpose conjugate. Acta Hort. 130:179-181. Ahrens, U., K. H. Lorenz, and E. Seemiiller. 1993. Genetic diversity among mycoplasmalike organisms associated with stone fruit diseases. Mol. Plant-Microbe Interact. 6:686-691. Alrefai, R H., P. J. Shiel, 1. 1. Domier, J. D. D'Arcy, P. H. Berger, and S. S. Korban. 1994. The nucleotide sequence of apple mosaic virus coat protein gene has no similarity with other Bromoviridae coat protein genes. J. Gen. Virol. 75:2847-2850. Alskieff, J., and P. Villemur. 1978. Greffage in vitro d'apex sur des plantules decapitees de Pommier (Malus pumila MilL) C R Acad Sci Ser D 287:1115-1118. Bachman, E. J., S. W. Scott, G. E. Xin, and V. B. Vance. 1994. The complete nucleotide sequence of prune dwarf ilarvirus RNA3: implications for coat protein activation of genome replication in ilarviruses. Virology 201:127-131. Bar-Joseph, M., and G. P. Martelli. 1991. Capillovirus group. In: R I. V. Francki, C. M. Fauquet, D. 1. Knudson, and F. Brown. (eds.). Classification and nomenclature of viruses. Fifth Report of the Int. Committee on Taxonomy of Viruses. Springer, Wien, New York, p. 339-340. (Arch. Virol. Suppl. 2). Barlass, M., K. G. M. Skene, R C. Woodham, and L. R Krake. 1982. Regeneration of virusfree grapevines using in vitro apical culture. Ann. Appl. BioI. 101:291-295. Bawden, F. C. 1964. Plant virus diseases. Ronald Press, New York. Bernhard, R, C. Marenaud, and D. Surie. 1969. Le pecher GF 305, indicateur polyvalent des virus des especes a noyaux. Ann Phytopath. 1(4):603-617. Bertaccini, A., 1. Carraro, D. 1. Davies, M. Laimer da Camara Machado, M. Martini, S. Paltrinieri, and E. Seemiiller. 2000. Micropropagation of a collection of phytoplasma strains in periwinkle and other host plants. 13th Int. Congr. 10M, ACROS Fukuoka, Japan, July 14-19 2000. Bertheau, Y., D. Frechon, I. Toth, and 1. J. Hyman. 1998. DNA amplification by Polymerase Chain Reaction (PCR). p. 39-59. In: M. C. M. Perombelon and J. M. van der Wolf (eds.), Methods for the detection and quantification of Erwinia carotovora subsp. atroseptica on potatoes. Occasional Publ. 10. Scottish Crop Res. Inst. Blattny, c., V. Seidl, and M. Erbenova. 1963. The apple proliferation of various sorts and possible strain differentiation of the virus. Phytopath. Medit. 2:116-123. Blok, V. c., J. Wardell, C. A. Jolly, A. Manoukian, D. J. Robinson, M. 1. Edwards, and M. A. Mayo. 1992. The nucleotide sequence ofRNA-2 of raspberry ringspot nepovirus. J. Gen. Virol. 73:2189-2194. Boscia, D., and A. Myrta. 1998. Serological detection of viruses included in certification protocols for stone fruits, Options Mediterraneennes, Serie B 19, Stone fruit viruses and certification in the Mediterranean: problems and prospects. p. 171-190. Boxus Ph, and M. Quoirin. 1974. La culture de meristemes apicaux de quelques especes de Prunus. Bul. Soc. R Bot. Belg. 107:91-101. Boxus, Ph., and Ph. Druart. 1986. Virus-free trees through tissue culture. p. 24-30. In: Y. P. S. Bajaj (ed.), Biotechnology in agriculture and forestry Vol. 1 Trees. Springer Verlag, Berlin, Heidelberg. Brants, D. H., W. Graafland, and C. P. Kerling. 1962. The distribution of tobacco mosaic virus in excised tomato roots cultivated in vitro. T. PI. Ziekten 68:198-207. CABIIEPPO. 1992. Plum pox potyvirus. p. 976-981. In: Organismes de quarantaine pour l'Europe.
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
225
Cambra M., A. Olmos, M. Asenio, O. Esteban, T. Candresse, M. T. Garris, D. Boscia, and A. Hadidi. 1998. Detection and typing of Prunus viruses in plant tissues and in vectors by print and spot-capture PCR, heminested PCR and PCR-ELISA. Acta Hort. 472:257-263. Campbell, A. I. 1962. Apple virus inactivation by heat therapy and tip propagation. Nature 195:520. Campbell, A. I. 1968. Heat sensitivity of some apple viruses. Tagungsber. (DAL DDR) Berlin 97:311-316. Campbell, A. I., and M. W. Best. 1964. The effect of heat therapy on several apple viruses. Rep. Long Ashton Res. Sta. 1963:65. Candresse, T. (2001). Advances in the methods of pathogen detection-introductory remarks. Acta Hort. 550:33-36. Candresse T., S. A. Kofalvi, M. Lanneau, and J. Dunez. 1998. A PCR-ELISA procedure for the simultaneous detection and identification of prunus necrotic ringspot and apple mosaic ilarviruses. Acta Hart. 472. Candresse, T., M. Lanneau, F. Revers, S. Kofalvi, and G. Macquaire. 2000. PCR-based techniques far the detection of plant viruses and viroids. Acta Hort. 530:61-67. Candresse T., M. Lanneau, F. Revers, N. Grasseau, G. Macquaire, S. German, T. Malinowsky, and J. Dunez. 1995. An immunocapture PCR assay adapted to the detection and the analysis of the molecular variability of the apple chlorotic leafspot virus. Acta Hort. 386:136-147. Carraro, L., L. Nemchinov, and A. Hadidi. 1998. PCR detection of pome and stone fruit phytoplasmas from active ar dormant tissue. Acta Hart. 472:731-735. Casper, R 1973. Serological properties of prunus necrotic ringspot and apple mosaic virus isolates from rose. Phytopathology 63:238-240. Casper, R 1983. ELISA detection of ILAR viruses in fruit trees by antisera having strong heterologous reactions. Acta Hart. 130:143-144. Casper, R, and S. Meyer. 1981. Die Anwendung des ELISA-Verfahrens zum Nachweis pflanzenpathogener Viren. Nachrichtenblatt Dt. Pflanzenschutzdienst (Braunschweig) 33(2):49-54. Cassells, A. C. 1983. Chemical control of virus diseases of plants. p. 119-155. In: G. P. Ellis and G. B. West (eds.), Progress in medicinal chemistry Vol. 20. Elsevier Science, Amsterdam. Cassells, A. c., and R D. Long. 1982. The elimination of potato viruses X, Y, Sand M in meristem and explant cultures of potato in the presence of virazole. Potato Res. 25:165-173. Clark, M. D., and A. N. Adams. 1977. Characteristics of enzyme-linked immuno-sarbent assay far the detection of the microplate method of plant viruses. J. Gen. Virol. 34:475-483. Clark, M. D., C. L. Flegg, M. Bar-Joseph, and S. Rottem. 1978. The detection of Spiroplasma citri by enzyme-linked immunosarbent assay (ELISA). Phytopathol. Z. 92:332-337. Cociu, V., D. Dragoi, and A. N. Popescu. 1997. Gene sources far breeding new plum (Prunus domestica L.) varieties with tolerance to plum pox virus (Sharka). Hort. Sci. (Budapest) 29:52-56. Costes, E., A. Audubert, S. Jaffuel, M. Jay, M. N. Demene, and J. Lichou. 1995. Developpement du fruit en relation avec la croissance vegetative chez l'abricotier Prunus armeniaca L. cv. "Rouge de Roussillon." Canad. J. Bot. 73:1548-1556. Cropley, R 1968a. Virus interference in fruit trees. Tagungsber. (DAL. DDR) Berlin 97: 235-240. Cropley, R. 1968b. Comparison of some apple latent viruses. Ann. Appl. BioI. 61:361-372. Cropley, R. 1968c. Synergism and interference between necrotic ringspot virus and prune dwarf virus in fruit trees. Tagungsber. (DAL. DDR) Berlin 97:139-192.
226
M. LAIMER
Crossley, S. J., V. Jacobi, and A. N. Adams. 1998. IC-PCR amplification of apple stem grooving virus isolates and comparison of polymerase and coat protein gene sequences. Acta Hort. 472. Crosslin, J. M., R. W. Hammond, and F. A. Hammerschlag. 1992. Detection of prunus necrotic ringspot virus serotypes in herbaceous and prunus hosts with a complementary RNA probe. Plant Dis. 76:1132-1136. da Camara Machado, A., and M. Laimer da Camara Machado. 1995a. Genetic transformation in Prunus armeniaca L. (apricot). p. 246-260. In: Y. P. S. Bajaj (ed.), Biotechnology in agriculture and forestry. Plant protoplasts and genetic engineering VI. Vol. 34. Springer Verlag, Berlin, Heidelberg. da Camara Machado, A., E. Knapp, G. Seifert, H. Piihringer, V. Hanzer, H. Weiss, Q. Wang, H. Katinger, and M. Laimer da Camara. 1995b. Gene transfer methods for the pathogen mediated resistance breeding in fruit trees. XXIV ISHS Congress, Kyoto, 1994. Acta Hort. 392:193-202. da Camara Machado, A., E. Knapp, V. Hanzer, W. Arthofer, D. Mendonc;a, S. Lopes, H. Katinger, and M. Laimer da Camara Machado. 1998. Phytosanitary improvement of fruit trees: Diagnostic strategies in virus indexing of in vitro plants. Int. Symp. on Fruit Tree Viruses. June 1997. Beltsville, Acta Hort. 472:511-516. Davies, D. L., and A. N. Adams. 2000. European stone fruit yellows phytoplasmas associated with a decline disease of apricots in southern England. Plant Pathol. 49:635-639. Davies, D. L., and M. F. Clark. 1994. Maintenance ofMLOs occurring in Pyrus species by micropropagation and their elimination by tetracycline therapy. Plant Pathol. 43:819-823. Dawson, W.O., J. L. White, and G. L. Grantham. 1978. Effect of heat treatment upon cowpea chlorotic mottle virus ribonucleic acid replication. Physiol. Biochem. 68:1042-1048. de Sequeira, O. A., and A. F. Posnette. 1969. Apple stem grooving. Commonw. Bur. Hort. PI. Crops. Tech. Commun. 30, Suppl. 2/3/4, 76a. Desvignes, J. C. 1999. Virus diseases of fruit trees. CTIFL, Paris. Desvignes, J. C., and R. Boye. 1988. Different diseases caused by the chlorotic leaf spot virus on the fruit trees. Acta Hort. 235:31-38. Dhingra, K. L. 1972. Transmission of apple mosaic by natural root grafting. Indian J. Hort. 9:348-350. Diekmann, M., and C. A. Putter. 1996. FAO/IPGRI Guidelines for the safe movement of germplasm. Stone Fruits 16. Di Terlizzi, B. 1998. Biological diagnosis of virus and virus-like diseases: a special reference to stone fruits certification. Options Mediterraneennes, Serie B 19, Stone fruit viruses and certification in the Mediterranean: problems and prospects. p. 151-170. Di Terlizzi, B., J. M. Audergon, K. Caglayan, M. Djerbi, I. Gavriel, W. Khoury, A. Myrta, V. Pallas, M. Srhiri, C. Varveri., H. Zeramdini, and V. Savino. 1998a. Efforts to harmonise and promote a stone fruit certification scheme in the Mediterranean countries, Options Mediterraneennes, Serie B 19, Stone fruit viruses and certification in the Mediterranean: problems and prospects. p. 135-148. Di Terlizzi, B., K. Caglayan, I. Gavriel, A. Myrta, M. Srhiri, H. Zeramdini, J. M. Audergon, M. Djerbi, W. Khouri, V. Pallas, C. Varveri, and V. Savino. 1998b. Efforts to harmonize and promote a stone fruit certification scheme in the mediterranean countries. Acta Hort. 473:517-526. Engel, G. 1990. The importance of virus-free plant material in integrated fruit production. Acta Hort. 285:127-133. Flegg, C. L., and M. F. Clark. 1979. The detection of apple chlorotic leaf spot virus by a modified procedure of enzyme-linked immunosorbent assay. Ann. Appl. BioI. 91: 61-65.
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
227
Foissac, X., L. Svanella-Dumas, M. J. Dulucq, T. Candresse, and P. Gentit. 2001. Polyvalent detection of fruit tree tricho, capillo and foveaviruses by nested RT-PCR using degenerated and inosine containing primers (PDO-RT-PCR). Acta Hort. 550: 37-43. Fridlund, P. R 1965. Symptoms of necrotic ringspot and prune dwarf in several Prunus species. Plant Dis. Rptr. 49:288-292. Fridlund, P. R 1973. Distribution of chlorotic leafspot virus in apple budsticks. Plant Dis. Rptr. 57: 865-869. Fridlund, P. R 1983. Distribution of chlorotic leafspot virus on various length of apple budsticks in successive years. Acta Hort. 130:85-87. Fridlund, P. R 1989. Virus and viruslike diseases of pome fruits and simulating noninfectious disorders. Cooperative Extension College of Agriculture and Home Economics, Washington State Univ., Pullman. Fuchs, K 1980. Untersuchungen zum serologischen Nachweis mechanisch iibertragbarer Viren des Kernobstes. Tag.-Ber., Akad. Landwirtsch.-Wiss. DDR, Berlin 184:453-460. Fuchs, K, M. Griintzig, and B. Al Kai. 1988. Der serologische Nachweis mechanisch iibertragbarer Viren des Kern und Steinobstes. Nachrichtenblatt rur den Pflanzenschutz in der DDR, 42(10):208-211. Fulton, R W. 1970a. Prunus necrotic ringspot virus. C.M.I.!A.A.B. Descriptions of plant viruses. 5. Fulton, R W. 1970b. Prune dwarf virus. C.M.I/A.A.B. Descriptions of plant viruses. 19. Fulton, R W. 1972. Apple mosaic virus. CMIIAAB Descriptions of plant viruses. 83. Fulton, R W. 1981. Ilarviruses. p. 381. In: K Kurstak (ed.), Handbook of plant virus infections and comparative diagnosis. Elsevier, Amsterdam. Galzy, R, and H. Compan. 1968. Thermotherapie de quelques varietes de vigne presentant des symptomes de viroses. Vignes Vines 166:88. Gella, R, and P. Errea. 1998. Application ofthe in vitro therapy for ilarvirus elimination in three Prunus species. J. Phytopathol. 146:445-449. German, S., T. Candresse, M. Lanneau, J. C. Huet, J. C. Pernollet, and J. Dunez. 1990. Nucleotide sequence and genomic organisation of apple chlorotic leafspot closterovirus. Virology 179:104-112. Gheorghiu, K 1976. Studies on the physical and chemical control of apple proliferation in tree nurseries and bearing orchards. Acta Hort. 67:209-218. Gianotti, J., G. Morvan, and C. Vago. 1968. Micoorganismes de type mycoplasme dans les cellules liberiennes de Malus sylvestris L. atteint de la maladie des proliferations. CR Acad. Sci. (Paris), Ser. D. 267:76-77. Gibb, K. S., A. C. Padovan, and B. D. Mogen. 1995. Studies on sweet potato little-leafphytoplasma detected in sweet potato and other plant species in northern Australia. Phytopathol. 85:169-174. Gilmer, R M., G. I. Mink, J. R Shay, R F. Stouffer, and R C. McCrum. 1971. Latent viruses of apple: L Detection with woody indicators. New York State Agr. Expt. Sta. (Geneva) 1(10):1-9. Gotlieb, A. R, and G. J. Berbee. 1973. Line pattern of birch caused by apple mosaic virus. Phytopathology 63:1470-1477. Goussard, P. G., and J. Wiid. 1992. The elimination offanleafvirus from grapevines using in vitro somatic embryogenesis combined with heat therapy. South African J. Enol. Viticult. 13:81-83. Gundersen D. K, and L-M. Lee. 1996. Ultrasensitive detection of phytoplasmas by nestedPCR assays using two universal primer pairs. Phytopathologia Mediterranea 35:144-151. Guo, D., K Maiss, G. Adams, and R Casper. 1995. Prunus necrotic ringspot ilarvirus: nucleotide sequence of RNA3 and the relationship to other ilarviruses based on coat protein comparison. J. Gen. Virol. 76:1073-1079.
228
M. LAIMER
Hadidi, A, and R. W. Hammond. 1989. Construction of molecular clones far identification and detection of tomato ringspot and arabis mosaic viruses. Acta Hart. 235: 223-230. Halk, K L., H. T. Hsu, and J. Aebig. 1982. Properties of virus specific monoclonal antibodies to prunus necrotic ringspot (NRSV), apple mosaic (ApMV), tobacco streak (TSV), and alfalfa mosaic viruses (AMV) viruses. Phytopathology 72:953. (Abstr. 189). Hamilton, R. 1. 1991. Ilarvirus group. p. 389-391. In: R. 1. V. Francki, C. M. Fauquet, D. 1. Knudson, and F. Brown (eds.), Classification and nomenclature of viruses. Fifth Report Int. Committee on Taxonomy of Viruses. Springer, Wien, New York (Arch. Virol. Suppl. 2). Hammond, R. W., and J. M. Crosslin. 1995. The complete nucleotide sequence of RNA 3 of a peach isolate of prunus necrotic ringspot virus. Virology 208:1-5. Hammond, J., H. Piihringer, A da Camara Machado, and M. Laimer da Camara Machado. 1997. A broad-spectrum PCR assay combined with RFLP analysis for detection and differentiation of Plum Pox Virus serotypes and isolates. Int. Symp. on Fruit Tree Viruses. June 1997, Beltsville, Acta Hart. 472:483-490. Hansen, A. J., and 1. Green. 1983. Potential of ribavirin for tree fruit virus inhibition. Acta Hort. 130:183-184. Hansen, A J., and D. Lane. 1985. Elimination of apple chlarotic leafspot virus from apple shoot cultures by ribavirin. Plant Dis. 69:134-135. Hartmann, W. 1998. Breeding of plums and prunes resistant to Plum Pox Virus. Acta Virologica 42:230-232. Heinrich, M., S. Botti, 1. Caprara, W. Arthofer, S. Strommer, V. Hanzer, S. Paltrinieri, M. Martini, H. Katinger, A. Bertaccini, and M. Laimer da Camara Machado. 2001. Improved detection methods far fruit tree phytoplasmas. Plant Mol. BioI. Reptr 19:69-179. Hibino, H., and H. Schneider. 1970. Mycoplasma-like bodies in sieve tubes of pear trees affected with pear decline. Phytopathology 60:499-501. Hirth, 1. 1958. Evolution de la concentration du virus de la mosaique du tabac en fonction des constituants biochimiques-cellularis au cours de la croissance de tissue de tabac cultives in vitro. C.R. Acad. Sci. 247:1795-1797. Howell, W. K, J. Burgess, G. L Mink, 1. J. Skrzeczkowski, and G. 1. Zhang. 1995. Elimination of apple fruit and bark deforming agents by heat therapy. Acta Hart. 472: 641-646. Howell W. K, G. 1. Mink, S. S. Hurtt, J. A Foster and J. D. Postman. 1996. Select Malus clones for rapid detection of apple stem grooving virus. Plant Dis. 80:1200-1202. Huang, S. c., and D. F. Millikan. 1980. In vitro micrografting of apple shoot tips. HortScience 15:741-743. Hull, R. 1989. The movement of viruses in plants. Annu. Rev. Phytopathol. 27:313-340. Huth, W. 1978. Kultur von Apfelpflanzen aus Meristemen. Gartenbauwissenschaften 43:263-266. Iri, M., T. Shimura, H. Togawa, and K. Veno. 1982. Elimination of grapevine viruses by meristem tip culture. p. 807-808. In: A. Fujiwara (ed.), Plant tissue culture. Proc. 5th Int. Congr. Plant Tissue Cell Culture. Maruzen, Tokyo, ISHS International Warking Group on Fruit Tree Viruses. 1992. Acta Hart. 309:407-418. ISHS International Working Group on Fruit Tree Viruses. 1998. Acta Hart. 472:761-783. ISHS International Working Group on Fruit Tree Viruses. 2001. Acta Hart. 550:473-493. James, D., P. A. Trytten, D. J. MacKenzie, and G. H. Towers. 1997. Elimination of apple stem grooving virus by chemotherapy and development of an immunocapture RT-PCR for rapid sensitive screening. Ann. AppI. BioI. 131:459-470. Janick, J., and J. N. Moore. 1996. Fruit breeding, Vol. 1. Tree and tropical fruits. Wiley, New York.
4. DETECTION AND ELIMINATION OF VIRUSES AND PHYTOPLASMAS
229
Jarausch, W., C. Saillard, B. Helliott, M. Garnier, and F. Dosba. 1994. Differentiation of mycoplasmalike organisms (MLOs) in European fruit trees by PCR using specific primers derived from the sequence of a chromosomal fragment of the apple proliferation MLO. Appl. Environ. Microbiol. 60:2916-2923. Jarausch, W., M. Lansac, C. Saillard, J. M. Broquaire, and F. Dosba. 1998. PCR assays for specific detection of European stone fruit yellows phytoplasmas and its use for epidemiological studies in France. European J. Plant Pathol. 104:17-27. Jarausch, W., C. Saillard, J. Broquaire, M. Garnier, and F. Dosba. 2000. PCR-RFLP and sequence analysis of a non-ribosomal fragment for genetic characterization of European stone fruit yellows phytoplasmas infecting various Prunus species. Molec. Cell. Probes 14:171-179. Jelkmann, W. 1994. Nucleotide sequences of apple stem pitting virus and ofthe coat protein gene of a similar virus from pear associated with vein yellows disease and their relationship with potex- and carlaviruses. J. Gen. Virol. 75:1535-1542. Jelkmann, W., and R Keirn-Konrad. 1997. An immuno-capture polymerase chain reaction and plate-trapped ELISA for the detection of apple stem pitting virus. J. Phytopathol. 145:499-504. Jonard, R 1986. Micrografting and its applications to tree improvement. p. 31-48. In: Y. P. S. Bajaj (ed.), Biotechnology in agriculture and forestry Vol. 1 Trees, Springer Verlag, Berlin, Heidelberg. Jonard, R, J. Hugard, J. J. Macheix, J. Martinez, L. Mosella-Chancel, J. 1. Poessel, and P. Villemur. 1983. In vitro micrografting and its applications to fruit science. Scientia Hort. 20:147-159. Jones, O. P., and S. J. Vine 1968. The culture of gooseberry shoot tips for eliminating virus. J. Hort. Sci. 43:289-292. Kartha, K. K. 1984: Elimination of viruses. p. 577-585. In: Cell culture and somatic cell genetics of plants. Academic Press, New York. Kassanis, B. 1954. Heat therapy of virus infected plants. Ann. Appl. BioI. 41:470-474. Kegler, H., H. B. Schmidt, and D. Trifonov. 1964. Identifizierung, Nachweis und Eigenschaften des Scharkavirus der Pflaume (Plum Pox Virus). Phytopath. Z. 50:97-111. Kegler, H., and C. Schade. 1971. Plum pox virus. C.M.I.IA.A.B. Descriptions of plant virus. 70. Kerlan, c., and J. Dunez. 1979. Differenciation biologique et serologique de souches de virus de la Sharka. Ann. Phytopath. 11:241-250. Kinard, G. R, S. W. Scott, and O. W. Barnett. 1996. Detection of apple chlorotic leaf spot and apple stem grooving viruses using RT-PCR Plant Dis. 80:616-621. Kison, H., B. C. Kirkpatrick, and E. Seemiiller. 1997. Genetic comparison ofthe peach yellows leaf roll agent with European fruit tree phytoplasmas of the apple proliferation group. Plant Pathol. 46:1-7. Knapp, E., V. Hanzer, H. Weiss, A. da Camara Machado, Q. Wang, B. Weiss., H. Katinger, and M. Laimer da Camara. 1995a. New aspects of virus elimination in fruit trees. XVI ISHS Symposium on Fruit Tree Viruses. Rome. Acta Hort. 386:409-418. Knapp, E., V. Hanzer, H. Weiss, A. da Camara Machado, Q. Wang, B. Weiss, H. Katinger, and M. Laimer da Camara. 1995b. Distribution of ACLSV in apple shoots cultivated in vitro. XVI ISHS Symposium on Fruit Tree Viruses. Rome, 1994. Acta Hort. 386:187-194. Knapp, E., A. da Camara Machado, H. Piihringer, Q. Wang, V. Hanzer, B. Weiss, H. Weiss, H. Katinger, and M. Laimer da Camara Machado. 1995c. Localization of fruit tree viruses by immuno-tissue printing in infected shoots of Malus sp. and Prunus sp. J. Virol. Methods 55:157-173.
230
M. LAIMER
Knapp, K, V. Hanzer, D. MendonI;>. >I;>.
Table 5.1.
(continued) Substrate used for extraction
Extraction method
Analysis
Species
Cultivars
Code
Year
Authors
23
1966
Romani and Ku
Intact fruit
Static headspace
GC
Pyrus communis
Bartlett
24
1967
Giannone and Baldrati
Fruit puree, nectars
Static heads pace, distillationextraction, derivatives formation
GC,TLC
Pyrus communis
Bartlett, Bose, Curato, Diel, Olivier de Serres, Passe Crassane
25
1968
PhanChon-Ton
Intact fruit
Static headspace
GC
Pyrus communis
Bartlett, Passe Crassane
26
1969
Fidler and North
Adsorption
Chemical reaction
Pyrus communis
Bose, Conference, Doyenne du Cornice
27
1969
Gasca et al.
Juice concentrate
GC
Pyrus communis
28
1970
Creveling and Jennings
Essence
Solvent extraction
GC, IR, UV, NMR
Pyrus communis
Bartlett
29
1970
Paillard et al.
Intact fruit
Headspace
GC
Pyrus communis
Passe Crassane
30
1973
Scotts and Wills
Cored sliced fruit
Vacuum sublimation
GC
Pyrus communis
Bartlett
31
1974
Jennings and Tressl
Intact fruit
Dynamic headspace
GC
Pyrus communis
Bartlett
N ..,.
CJ1
32
1974a
Strandjev
Essence
Solvent extraction
GC
Pyrus communis
Bartlett, Passe Crassane
33
1974b
Strandjev
Essence
Solvent extraction
GC
Pyrus communis
Bartlett, Passe Crassane
34
1977
Ghena et al.
Juice
Solvent extraction
GC
Pyrus communis
Bartlett
35
1977
Quamme and Marriage
Blended fruit
Solvent extraction
UV, IR, LC
Pyrus communis
Anjou, Aurora, Barseck, Bartlett, Bose, Clara Frijs, Corneille, Courielle, Dr. Jules Guyot, Ewart, Flemish Beauty, HW602, Kieffer, Yakima, Laxtons progress, Mac, Magness, Max Red, Maxine, Merton Pride, Moonglow, NY 8760, Parbarton, Pierre, Progress, Russett Bartlett, Seckel, Stewarts Bartlett, Surecrop
36
1978
Janes and Frenkel
Homogenate
Static headspace
GC
Pyrus communis
Bose
37
1981
Russel et al.
Blended fresh and canned fruit
Simultaneous distillation/ extraction
GC, HPLC-UV
Pyrus communis
Bartlett, Kieffer, Magness
38
1982
Strandjev
Essence
Solvent extraction
GC
Pyrus communis
Beurre Williams, Passe Crassane
39
1983
Romani et al.
Intact fruit
Static headspace
GC,MS
Pyrus communis
Bartlett
N >f;:.
0)
Table 5.1.
(continued)
Code
Year
Authors
40
1984
Quamme
41
1985
Berger et al.
Substrate used for extraction
Extraction method
Analysis
Species
Cultivars
Blended fruit and shoot
Solvent extraction, simultaneous distillation/ extraction
UV, HPLC-UV
Pyrus communis
Anjou, Aurora, Barseck, Bartlett, Beurre Superfine, Bose, Clara Frijs, Courielle, Dr. Jules Guyot, Ewart, Harvest Queen, Highland, HW603, HW606, HW607, Kieffer, Yakima, Laxtons Progress, ~ac, ~agness, ~ax Red, ~axine, ~oonglow, NY 8760, Parbarton, Russett Bartlett, Seckel, Stewarts Bartlett, Surecrop
Homogenate
Solvent extraction
GC/GC-~S/
Pyrus communis
Bartlett
UV
Pyrus communis
Anjou
GC
Pyrus communis
Bartlett
Pyrus communis
Bartlett, La France
Pyrus communis
Bartlett
GCO 42
1990
Chen et al.
Intact fruit
43
1990
Ke et al.
Juice
44
1990
Shiota
Peeled and cored sliced fruit
45
1991
Berger
Solvent extraction
Simultaneous distillation/ solvent extraction
GC,
GC
GC-~S
N
~
'1
46
1991
Rizzolo et a1.
Sliced flesh
Static heads pace
GC, GC-MS
Pynzs communis
Passe Crassane
47
1992
Horvat et a1.
Blended peeled fruit
Simultaneous steam distillation/ solvent extraction
GC, GC-MS
Pyrus pyrifolia
Chojui, Hosui, Kosui, Ya Li, Shinko
48
1992
Nanos et a1.
Juice, suspension cultured fruit cells
Static headspace
GC
Pynzs communis
Bartlett
49
1992
Takeoka et a1.
Blended and intact fruit
Simultaneous vacuum distillation/ extraction, dynamic headspace
GC, GC-MS
Pynzs pyrifolia
Seuri
50
1993
Chen et a1.
Intact fruit
Solvent extraction
UV
Pynzs communis
Anjou
51
1993
EccherZerbini et a1.
Sliced fruit flesh
Static headspace
GC, GC-MS
Pynzs communis
Conference, Doyenne du Cornice
52
1994
Avelar et a1.
Intact fruit, pulp
Dynamic headspace, supercritical fluid extraction
GC, GC-MS
Pynzs communis
Rocha
53
1994b
Ke et a1.
Juice
Static headspace
GC
Pynzs communis
Bartlett
54
1995
Imayoshi et a1.
Intact fruit, blended peel and pulp
Dynamic headspace, steam distillation
GC, GC-MS
Pynzs x bretshneideri
Ya Li
N
"'"
~
Table 5.1.
(continued)
Substrate used for extraction
Extraction method
Analysis
Species
Cultivars
Code
Year
Authors
55
1995
Richardson and Kosittrakun
Intact fruit
Static headspace
GC
Pyrus communis
Anjou, Bartlett
56
1996
Suwanagul
Intact fruit
Dynamic headspace, SPME
GC, GC-MS, GCO
Pyrus communis
Anjou, Bartlett, Bose, Doyenne du Cornice, Forelle, Packham's Triumph, Seckel, Vicar of Winkfield
57
1997a
Beurle and Schwab
Blended cored fruit
Solvent extraction
GC, GC/MS, MDGC
Pyrus communis
Alexander Lucas, Bartlett, Gute Luise, Gellerts, Madame Vertl:'3, Vereinsdechant, Packham's Triumph
58
1997
Chen and Varga
Intact fruit
Solvent extraction
UV
Pyrus communis
Anjou
59
1997
De Vries et al.
Intact fruit
Headspace
Laser-based photoacoustic spectroscopy
Pyrus communis
Conference
60
1997
Kjaersgaard et al.
Juice
Dynamic headspace (purge and trap)
GC, GC-MS
Pyrus communis
Clara Frijs
61
1997
Lange
Peeled fruit tissue
Static headspace
GC
Pyrus communis
Bartlett
62
1997
Recasen et al.
Juice
GC
Pyrus communis
Conference
N
~ (.0
63
1997
Yang and Lee
64
1998
EccherZerbini and Grassi
Pulp
Headspace
65
1998
Giintert et al.
Pulp
Simultaneous distillationl extraction dynamic
66
1998
Xu et al.
Flesh
67
1998
Oshita et al.
68
1998
69
Pyrus pyrifolia
Niitaka
Pyrus communis
Conference
GC, MS, NMR, IR, GCO
Pyrus communis
Bartlett
Distillation
GC-MSMDGC
Pyrus x bretshneideri
Ya Li
Intact fruit
Headspace
Electric odor sensor
Pyrus communis
La France
Rizzolo et al.
Pulp
Solvent extraction
GCIGCO
Pyrus communis
Doyenne du Cornice
1998
Zoffoli et al.
Peel discs
Solvent extraction
UV
Pyrus communis
Anjou, Bartlett, Packham's Triumph
70
1999
Chervin et al.
Peeled and cored fruit
GC, enzymatic assays
Pyrus communis
Packham's Triumph
Juice Intact, blended fruit
Static headspace
GC
Pyrus seratina
Niitaka, Shinsui
SPME
GC
Pyrus communis
Packham's Triumph
Pyrus communis
Conference
Pyrus communis
Anjou
71
1999
Park et al.
72
2000
Chervin et al.
73
2000
EccherZerbini et al.
74
2000
Ju and Curry
GC
Static headspace
Intact fruit, tissue discs
SPME
GC, GC-MS
N
c.n
0
Table 5.1.
(continued)
Code
Year
Authors
Substrate used for extraction
75
2000
Ju et a1.
Blended flesh
Static headspace
GC
Pyrus x bretshneideri
Ya Li, Laiyang Chili
76
2000
Lo Scalzo et a1.
Fruit peel discs
Solvent extraction
GC-MS
Pyrus communis
Conference
77
2000
Oshita et a1.
Flesh, intact fruit
Static headspace
GC, electric odor sensor
Pyrus communis
La France
78
2001
Ju et a1.
Intact fruit
SPME
GC-MS
Pyrus communis
Bartlett
79
2001
Pinto et a1.
Juice
Static headspace
GC
Pyrus communis
Blanquilla
80
2001
Kharlamov and Burrows
Intact fruit
81
2001
Rapparini and Predieri
Sliced flesh
Pyrus communis
Harrow Sweet
Extraction method
Analysis
Species
Cultivars
Laser-based photoluminescence spectroscopy Dynamic headspace
GC/MS
Ge, gas chromatography; GCO, gas chromatography olfactometry; IR, infrared spectroscopy; MD-GC, multidimensional gas chromatography; MS, mass spectrometry; NMR, nuclear magnetic resonance; SPME, solid phase microextraction; TLC, thin layer chromatography, UV, ultraviolet spectroscopy.
5. PEAR FRUIT VOLATILES
251
Difficulties in fruit volatile isolation and analysis may arise for several reasons including concentration level of the volatile compounds, complexity of the aroma mixture, physical and chemical diversity, and instability (Parliment 1998). Pear flavor constituents are usually present in extremely low concentrations (parts per million, billion, or trillion) relative to the total fruit weight (Takeoka et al. 1992; Suwanagul and Richardson 1998b). Pear volatiles are extremely complex mixtures and may consist of hundreds of individual components, and physical and chemical properties of the different volatiles vary. Flavor composition usually includes a wide variety of different chemical classes (saturated and unsaturated hydrocarbons, organic acids, esters, aldehydes, alcohols, ketones, oxides, terpenes, and sulphur compounds) that cover a wide range of polarities, solubilities, volatilities, and pH values (Suwanagul and Richardson 1998b), thus the extraction and separation can be difficult. A further problem complicating the study of pear aroma is the formation of artifacts as a consequence of the instability of many volatile components, which may be oxidized by the air, and/or degraded by heat or extreme pH values. Other chemical processes, including photodecomposition, adsorption, vaporization, and fermentation due to microbial action, can also occur in the sample between the time of collection and analysis (Takeoka and Full 1997). Long sampling times increase the possibility that these processes may occur during sample isolation (Heath and Reineccius 1986). Because many pear volatile compounds are present in trace amounts, additional volatiles can be present as impurities due to contamination from surfaces that the sample contacts (Takeoka and Full 1997) or to residue of pesticides applied in the orchard (Nijssen 1991). In addition to chemically-induced changes, the possibility of secondary volatile production via enzymatic reactions must be considered. When fruit is cut, crushed, homogenized, or blended, certain enzymatic processes may be activated, some of which are extremely rapid once cellular disruption begins. This leads to the production of many volatiles, which normally occur only in trace amounts or not at all in intact cells (Heath and Reineccius 1986; Takeoka and Full 1997). A. Sample Preparation
Studies on pear volatiles can be divided in two groups according to the physiological state of the starting fruit sample: (1) Examinations of the volatiles released from intact fruit. This methodology considers only the odor compounds normally produced in the living pear tissue and
252
F. RAPPARINI AND S. PREDIERI
perceived directly in the nose before consumption. Sampling from intact fruits also allows for time-course studies (Mattheis et al. 1991); (2) Methods in which fruits are fragmented, blended, or homogenized to a lesser or greater degree, prior to or during the analysis. Cell disruption removes barriers to diffusion and thus allows for the determination of volatile composition and concentration inside the fruit tissue. However, because previously compartmentalized enzymes and substrate mix, new volatiles are formed. The ability to form volatiles after cell disruption can change during fruit ripening, apparently because of changes in enzyme and substrate availability (Baldwin et al. 2000). This procedure mimics the release of aromatic volatiles in the mouth during chewing and thus reflects the aroma perceived in the nose retro-nasally (Rothe 1988; Chervin et al. 2000). In order to study whether particular volatiles are present in the intact fruit or whether they are only formed following cell disruption, different methods of enzyme inactivation can be applied, including addition of either methanol or saturated solution of calcium chloride, and rapid heating by microwave (Schreier 1984; Takeoka et al. 1992; Buttery and Ling 1993). To be as close as possible to the development of volatiles released upon chewing, the enzyme inhibitor can be added immediately after pulp maceration (Chervin et al. 2000). The presence of the peel in the analyzed sample also constitutes an important factor, since a different volatile profile has been found between epidermal tissue (peel) and parenchima tissue (pulp) (Berger 1991; Chervin et al. 2000; Lo Scalzo et al. 2002). B. Isolation and Concentration of Pear Volatiles
Most of the methodologies employed in pear volatile studies involve classical procedures of flavor isolation: distillation and/or solvent extraction, and concentration of headspace volatiles. These procedures utilize differences in vapor pressure (distillation and headspace) or solubilities in different solvents (extraction). Direct solvent extraction has been widely used to isolate fruit volatiles of various pear cultivars (Gasca 1969; Creveling and Jennings 1970; Strandjev 1974a,b; Quamme and Marriage 1977; Quamme 1984; Berger et al. 1985a; Chen et al. 1993; Avelar et al. 1994; Beuerle and Schwab 1997a; Rizzolo 1998; Zoffoli et al. 1998; Cigic and Zupancic-Kralj 1999; Lo Scalzo et al. 2002). It has proven to be an effective extraction method yielding a large number of analytes, including highly water-soluble flavor constituents, which are typically poorly recovered by distillation and headspace analysis (Takeoka and Full 1997). However, the extract may contain semi- and nonvolatile constituents (Rothe 1988). Solvent choice
5. PEAR FRUIT VOLATILES
253
is an important factor to consider for optimum recovery of pear volatiles (Leahy and Reineccius 1984). Solvents are usually selected because of their selectivity and boiling point. The most frequently used volatile organic solvents in preparation of pear volatile extracts have been ethyl chloride and diethyl ether. Less polar solvents include pentane, isopentane, hexane, iso-octane, dichloromethane, alone or in combination. Diethyl ether has been widely employed as its lower boiling point permits excess solvent to be easily removed and it has a high extraction capacity for a broad spectrum of volatile compounds (Schultz et al. 1977). Distillation is among the oldest methods used for selective extraction of volatile compounds from pear aqueous matrices (Table 5.1). The advantage over other isolation methods (e.g., solvent extraction) is the separation of non- or semivolatile materials, normally present in high amounts, from highly volatile compounds (Schreier 1984). This technique often requires an additional step in which samples must be extracted from the distillate and concentrated so as to reach a detectable level (Coulibaly and Jeon 1996). This can involve solvent extraction and concentration, adsorption techniques, or freezing. The most frequently used distillation method for isolating pear volatiles has been steam distillation (Harley and Fisher, 1927; Leonard et al. 1954; Luh et al. 1955; Claypool et al. 1958; Spanyar et al. 1964, 1965; Heinz et al. 1966; Paillard et al. 1970; Imayoshi et al. 1995). The steam and volatiles are usually condensed in a series of cooled traps. The contents of the traps are combined and solvent extracted. This methodology is timeintensive and is subject to artifacts from solvent and/or for heat-sensitive compounds (Rothe 1988). Vacuum distillation method has been applied in several studies of pear volatiles, to minimize artifact formation by thermal degradation or hydrolysis, but is semiquantitative at best (Gasca et al. 1969; Giintert et al. 1998). As an alternative, simultaneous distillation-extraction (SDE) in a specialized apparatus such as the Licken/Nickerson (L/N) system has been used to produce the organic concentrates from pear fruits (Russell et al. 1981; Quamme 1984; Shiota 1990; Horvat et al. 1992; Takeoka et al. 1992; Giintert et al. 1998). Even though this technique exposes the sample to high temperatures and is known to produce thermally generated artifacts, it has been used in fruit flavor research as it can simulate the composition of volatiles that would be formed during processing such as canning (Takeoka and Full 1997). Using SDE, volatiles can be quickly extracted with a small amount of solvent in a single step within a shorter time as compared to lengthy distillation followed by extraction (Coulibaly and Jeon 1996). Heinz et al. (1966) compared solvent extraction, steam distillation and adsorption methods to analyze essences deriving from 'Bartlett'
254
F. RAPPARINI AND S. PREDIERI
pear processing. The major qualitative difference between the isolation methods was found to be in the relative proportion of high- to lowboiling point compounds. They found that the direct solvent extract and steam-distilled samples tend to contain a lower portion of low-boiling point compounds compared to charcoal absorption samples. The highboiling point compounds were similar among all extraction methods. Gtintert et al. (1998) found that the composition of the extract obtained by simultaneous distillation-extraction under vacuum is similar to that obtained by vacuum steam distillation (syn. vacuum headspace sampling method), suggesting that the former is the closest alternative to the latter method. In almost every case, distillation and solvent extraction methods require not only large amounts of sample, but also large volumes of organic solvents in certain steps of the preparation. The problems related to excessive use of solvent have been pointed out by several workers (Jennings 1961; Schreier 1984; Rothe 1988; Shiota 1990; Takeoka et al. 1992), and include concern for environmental pollution, an increased probability of sample contamination due to solvent-borne impurities, the risk of masking of volatile compounds by the solvent peak, and the loss of analytes. Extraction with liquid carbon dioxide (C0 2 ) or supercritical fluid extraction (SFE), is a more selective and efficient alternative to avoid problems encountered in extraction with low-boiling point organic solvents, and has been applied in isolation of volatiles from several fruits including pears (Polesello et al. 1993; Avelar et al. 1994). A major advantage of SFE using supercritical CO 2 is the low extraction temperature. Furthermore CO 2 is inexpensive, nonflammable, nonexplosive, chemically inert, readily available in a pure state, and leaves no toxic residue in the extract (Maarse 1991). Some authors, however, express doubts about the ability of this solvent to extract all compounds quantitatively (Taylor and Linforth 1994). Analyses of volatile components in the vapor phase above the matrix sample (headspace) were performed in pears as early as 1927 by Harley and Fisher. The headspace sampling system (Fig. 5.1) is becoming a powerful technique not only for the analysis of fruit samples (Dirinck et al. 1984; Ibanez et al. 1999), and food samples such as olive oil (Rapparini and Rotondi 2002), but is also widely employed in ecological and environmental studies (Bicchi and Joulain 1990; Charron et al. 1996, Ruther and Hilker 1998; Jacobsen 1997; Takeoka and Full 1997; Hewitt 1998; Baraldi et al. 1999; Butrym and Hartman 1999; Mendes et al. 2000; Rapparini et al. 2000a; Rapparini et al. 2001), investigations on tissue cultures physiology (Predieri et al. 1999; Rapparini et al. 2000b), in forensic science (Goldbaum et al. 1964; Pohl and Keller 1985), and in perfume research (Bedoukian et al. 1979). Headspace sampling tech-
5. PEAR FRUIT VOLATILES
Fig. 5.1.
255
Headspace sampling of sliced pears (Photo F. Rapparini)
nique has been reviewed elsewhere (Schaefer 1981; Jacobsen 1997). Some advantages are the relatively small amount of sample required, the reduced probability of artifact formation and sample loss, and the simplicity of sampling, that allows for minimum time-gap from sampling to chemical analysis (Teranishi 1998). This sampling procedure is the most direct way of qualitatively and quantitatively measuring volatile compounds released from the sample matrix, that is the part directly detected by smell (Maarse 1991). This is much more meaningful than total volatile analysis for correlating chemical and sensory analyses (Dirinck et al. 1984; Teranishi 1998; Ibanez et al. 1999). Headspace sampling of pear volatiles has been reported for intact, sliced, or crushed pears, as well as whether aqueous or alcoholic pear distillates were used (Table 5.1). Because volatiles are present at low levels in the gas phase above the sample, a concentration procedure is necessary. Enrichment can be achieved by the use of two major techniques: static and dynamic headspace sampling.
256
F. RAPPARINI AND S. PREDIERI
Using the static headspace technique, the sample is enclosed in a gastight container and, after equilibration, a small volume of the accumulated vapors present in the gas phase over the matrix (headspace) is collected with a syringe and directly injected into a gas chromatograph. This technique is preferred when automation is required, as in quality control methods or in sample screening (Dirinck et al. 1984; Manura and Overtone 2001). Direct analysis of equilibrium headspace vapor has been employed widely to isolate pear volatiles (Buttery and Teranishi 1961; Romani and Ku 1966; Giannone and Baldrati 1967; Paillard et al. 1970; Janes and Frenkel 1978; Romani et al. 1983; Rizzolo et al. 1991; Eccher-Zerbini et al. 1993; Richardson and Kossittrakun 1995; Lange 1997; Eccher-Zerbini and Grassi 1998; Chervin et al. 2000; EccherZerbini 2000; Oshita et al. 2000; Pinto et al. 2001). Giannone and Baldrati (1967) found that directly injecting headspace samples from pear fruits allowed for the detection of low-boiling point compounds not detected with solvent extraction methodologies. However, this technique did not allow for detection of high-boiling point compounds due to insufficient partition into the gas headspace volume. Romani and Ku (1966) encountered similar limitations while isolating pear volatiles from 'Bartlett' fruits. Furthermore, Heath and Reineccius (1986) showed that only the most abundant volatiles can be analyzed, suggesting that this method is not adequate for isolation of trace volatiles. Therefore, in such a system, it becomes difficult to establish whether the additional volatiles analyzed are due to increased concentration in the headspace or are new products appearing as a consequence of altered metabolism in a closed system (PIotto 1998a). The dynamic headspace sampling technique or a dynamic flowthrough system allows for detection of high-boiling point compounds, such as those characteristic of pear fruits (decadienoate esters), and trapping of a much larger volume of headspace volatiles in order to obtain sufficient material for analysis (Dirinck et al. 1984). In this trapping system, the headspace vapors are purged with a gas stream (clean air or nitrogen) continuously flowing over or through the sample (purge and trap technique). Volatile compounds are concentrated from this headspace gas volume at the outlet of the container, generally by liquid absorption, solid adsorption, and cooling (cryogenic method) (Schaefer 1981). Solid adsorbents include charcoal or synthetic porous polymers such as the Porapak series, the Chromsorb series, and Tenax (Paillard et al. 1970; Jennings and Tressl 1974; Takeoka et al. 1992; Imayoshi et al. 1995; Suwanagul and Richardson 1998b; Rapparini and Predieri 2002). The relevant properties of the different adsorbents have been investigated in a number of studies (Matisova and Skrabakova 1995; Takeoka and Full 1997; Brancaleoni et al. 1999; Manura 2001). None of these
5. PEAR FRUIT VOLATILES
257
adsorbents is perfect in trapping all volatile compounds with the same efficiency and they all exhibit some selectivity; therefore, the selection of the adsorbents depends on the chemical properties and concentrations of the compounds of interest as well as on the purity of the sample (Heath and Reineccius 1986). Pear volatiles trapped on the adsorbents are eluted with solvents, or by thermal desorption, and subsequently analyzed by gas chromatography either on-line or off-line. Thermal desorption provides better recovery than solvent elution of all trapped compounds while avoiding co-elution of low-boiling point compounds with the solvent (Wampler 1997). Thermal desorption also limits the possibility of artifact formation originating from interactions between solute and solvent. However, only solvent desorption allows multiple injections from a single sample (PIotto 1998a). The first study of pear volatiles reported using dynamic headspace methods was carried out by Pan-Chon-Ton in 1965 who isolated volatiles from pear fruits of various cultivars. Jennings and Tressl (1974) used adsorption on Porapak Q followed by elution with pentane prior to gas chromatographic analysis. In the last 30 years, similar methods have been extensively used for studying pear volatiles (Paillard et al. 1970; Rizzolo et al. 1992; Takeoka et al. 1992; Avelar et al. 1994; Kjaesgaard et al. 1997; Giintert et al. 1998; Suwanagul and Richardson 1998; Cigfc and Zupancic-Kralj 1999; Chervin et al. 2000; Rapparini and Predieri 2002). The dynamic enrichment system offers many advantages over static headspace measurements, since the former concentrates the analytes to detectable levels over a wide range of concentration and molecular weight (Suwanagul1996; Rapparini and Predieri 2002). As air is flushed through the sampling container, the fruit is maintained under aerobic conditions, thus limiting the formation of artifacts (PIotto 1998a). This method is nondestructive, and sampling from intact fruits using this collection procedure allows for time-course studies. Both dynamic and static headspace methodologies allow scientists to design and modify the headspace apparatus to best accomplish specific experimental needs. However, several experimental parameters, including volume of air to be sampled, volume of the headspace system, sampling time and speed, and carrier flow rate (Bicchi and Joulain 1990), influence headspace composition, and hence, the analytical results and their reliability and consistency. The effects of these factors may be worthy of advanced investigations and should be taken into account when comparing results from different experimental systems and/or laboratories. Despite these problems and although solvent extraction remains a commonly applied method in pear aroma studies, a number of papers indicates that headspace sampling is an increasingly widespread technique and a promising research tool for the examination of pear fruit volatiles.
258
F. RAPPARINI AND S. PREDIERI
Recently, a relatively new absorption technique called solid-phase microextraction (SPME), developed by Pawliszyn and coworkers (Arthur and Pawliszyn 1990; Arthur et al. 1992; Potter and Pawliszyn 1992), is increasingly being applied in fruit flavor studies (Yang and Peppard 1994). It consists of a fused-silica fiber coated with a polymeric stationary phase that can be placed completely in the sample (immersion sampling) or in the headspace of the sample (Roberts et al. 2000). The volatile organic analytes are absorbed and concentrated in the coating and then thermally desorbed inside the injector port of a gas chromatograph (Zhang and Pawliszyn 1993). The detection limits of the headspace SPME technique have been claimed to be at the subpicogram level (Zhang and Pawliszyn 1995). In the last decade this method has been applied in fruit aroma studies including pear (Yang and Peppard 1994; Ibanez et al. 1998; Chervin et al. 2000; Ju and Curry 2000; Ju et al. 2001). Suwanagul and Richardson (1998a) have discussed advantages and disadvantages ofthis technique while isolating headspace volatiles of ripening pears. Static heads pace trapping of compounds by SPME over a fixed time allowed the authors to accurately follow the quantitative changes of particular volatile compounds such as a-farnesene or various decadienoate esters without excessive losses due to oxidation. SPME has proven to be a fast, simple, repeatable, and inexpensive method for the extraction, identification, and quantification of organic compounds from pears. This technique has the advantage over various solvent extractions or headspace methods of reducing losses of compounds due to extract concentration or to purged air streams, and of avoiding volatiles masking by solvent. C. Identification and Quantification of Compounds
Once pear volatiles have been collected, chemical separation and detection is used for qualitative and quantitative analysis. Until the advent of gas chromatography (GC), studies concerned with nonethylene emissions from pears were seriously handicapped and the qualitative and quantitative analysis done at that time were mainly based on classical organic chemistry techniques (Harley and Fisher 1927; Mattus 1950; Gerhardt 1954; Luh et al. 1955; Serini 1956). The decisive breakthrough in pear aroma analysis was closely related to the introduction of gas chromatography in the 1950s. The development of this technique has vastly improved the analysis of pear volatiles, resulting in more than 300 compounds being identified to date (Table 5.2). The advantages of GC include high separation effect; more flexibility of the separation conditions; a very low detection limit (from 10-5 to 10-12 ) (Scott 1998) which
5. PEAR FRUIT VOLATILES
259
is as low as human sense organs can detect; relatively rapid and reproducible analysis with a high degree of significance (Rothe 1988). The power of gas chromatography has been enhanced by the development of capillary columns, programmed temperature regimes, the use of organic polymers as stationary phases, and the introduction of more sensitive detection methods (nuclear magnetic resonance, mass spectrometry, Fourier transform infrared spectroscopy) (Rothe 1988).
Table 5.2.
Volatile compounds identified in pear fruits.
Compounds
References (Table 5.1 code)
Alcohols
Aliphatic alcohols Methanol Ethanol
n-Propanol 2-Propanol (iso-propanol) n-Butanol 2-Butanol 2-Methyl-l-propanol (iso-butanol) n-Pentanol (amyl alcohol) 2-Pentanol 2-Methyl-l-butanol 2-Methyl-2-butanol 3-Methyl-l- butanol (iso-pentanol) 3-Methyl-3-buten-2-ol n-Hexanol (E)-2-Hexen-l-ol 2-Methyl-l-pentanol n-Heptanol 3-Ethyl-l-pentanol n-Octanol n-Octen-3-ol (E)-2-0cten-l-ol
Octane-l,3-diol
7,9,24,25,32,33,34,38,70 13,21,24,25,27,29,30,32,33,34,38,43,46,48, 51,53,54,55,56,59,60,61,62,63,64,70,71,73, 75,77,79,81 21,24,25,27,56,65,81 13,27 18,21,22,24,25,29,30,32,33,34,38,44,46,51, 52,54,56,65,68,77,81 13,27 13,25,27,44,52,56,65,81 21,24,25,27,32,33,34,38,44,46,51,52,54,56, 68,81 13 27,44,52,54,56,65,68,81 27,51 13,24,27,46,51,54,65,81 68 13,21,22,39,44,46,49,51,52,54,56,65,66,68, 72,81 54,65,68 54 21,44,49,56 81 18,21,44,46,49,51,52,54,56,65,68,72,81 65 54 57,65
(continues)
260
Table 5.2.
F. RAPPARINI AND S. PREDIERI (continued)
Compounds
References (Table 5.1 code)
(Z)-5-0ctene-l,3-diol 2-Ethyl-l-hexanol 6-Methyl-5-hepten-2-ol n-Nonanol n-Decanol (E)-3-Decen-l-ol (Z)-3-Decen-l-ol (Z)-4-Decen-l-ol (E)-2-Decen-l-ol (E,E)-2,4-Decadienol n-Dodecanol n-Hexadecanol 2,3-Butylenglycol 2,6,10-Trimethyldodeca-2,7 -(E), 9-(E),11-tetraen-6-ol
57 14,44,52,54 54,72 54,56 49,54 49,54 54 49,54 54 54 54, 72 44
Aromatic alcohols Benzenethanol Phenylethanol
8
76 68 72
Aldehydes Aliphatic aldehydes Methanal (formaldehyde) Ethanal (acetaldehyde) Propanal Butanal Pentanal Hexanal 2-Hexenal (E)-2-Hexenal (E,E)- 2,4-Hexadienal Heptanal (E)-2-Heptenal 2-Methyl-2-pentenal (E,E)-Ethyl-4-pentenal Octanal (E)-2-0ctenal Nonanal n-Nonenal
24,32,33,34,38 1,2,7,23,24,27,30,32,33,34,36,38,43,46,48, 51,53,55,59,61,62,63,64,70,71,73,77,79 24,25,27,52 20,81 81 24,27,44,46,47,49,52,54,56,65,68,72,81, 27,56 44,47,49,52,54,68,72,81 81 81 68 68 52 81 72,81 44,72,81 81
261
5. PEAR FRUIT VOLATILES 2-Nonenal (E)-2- Nonenal
(E,Z)-2,6-Nonadienal Decanal 2,4-Decadienal (E,E)- 2,4-decadienal (Z,E)- 2,4-decadienal
2-Butyl-2-octenal
47 68 68 81 44,49 49,52,54,68 68 47
Aromatic aldehydes Benzaldehyde
47,60,81
Phenylacetaldehyde
49
Ketones Acetone 2-Butanone (methylethyl ketone) 3-Hydroxy 2-butanone (acetyl methyl carbinol; acetoin) 2-Pentanone (methylpropyl ketone) 1-Penten-3-one 2-Methylcydopentanone 2-Heptanone 6-Methyl-5-hepten-2-one 2-Undecanone 3,4-epoxy-3-ethyl-2-butyl ketone 2,3-Butanedione (diacetyl) Geranylacetone
24,25,46 24,44,46 7,8,44,52,65 24,68 52 68 68,81 56,72,81 68 66 7
81
Esters
Formates Methyl formate
25,27
Ethyl formate
13,25,32,33,34,38,54
iso-Propyl formate
27
Butyl formate Hexyl formate
81 81
Acetates Methyl acetate Ethyl acetate
13,21,23,25,29,31,33,38,39,46,52,77 13,18,21,22,23,24,25,27,30,31,32,33,34,38, 39,44,46,49,51,52,53,54,60,77,81
Propyl acetate
21,22,23,24,25,27,29,31,32,33,34,38,39,44, 49,52,54,56,65,81
Butyl acetate
18,21,22,23,24,25,27,29,30,31,32,33,34,38, 44,45,46,49,51,52,54,56,60,65,68,72,77,81 (continues)
262
Table 5.2.
F. RAPPARINI AND S. PREDIERI (continued)
Compounds
References (Table 5.1 code)
iso-Propyl acetate Pentyl acetate (amyl acetate)
20 18,20,21,22,23,24,25,29,31,32,33,34,38,44, 46,49,51,52,54,56,60,65,68,72,81
iso-Butyl acetate (2-methylpropyl acetate) tert-Butyl acetate 3-Methylbutyl acetate Uso-pentyl acetate; iso-amyl acetate) 2-Methylbutyl acetate 3-Methyl-2-butenyl acetate Hexyl acetate
(E)-2-Hexenyl acetate 4-Hexen-l-01 acetate 3-Hexen-l-ol acetate (Z)-3-Hexen-l-01 acetate (Z)-3-Hexenyl acetate 2-Methylpentyl acetate 5-Hexenyl acetate Heptyl acetate 3-Hepten-l-ol acetate Octyl acetate 4-0cten-l-ol acetate 3-0cten-l-ol acetate 2,4-0ctadien-l-ol acetate (E)-2-0ctenyl acetate Nonyl acetate Decyl acetate (E)-3-Decenyl acetate Prenyl acetate Phenylethyl acetate p-Phenylethyl acetate 2-Phenylethyl acetate
24,25,32,33,34,38,44,46,49,51,52,54,56,60, 68,81 27 27,29,44,49,54,56,81 44,49,54,81 49 16,21,22,23,24,25,29,30,31,32,33,34,38,39,44, 45,46,47,49,51,52,54,56,60,65,68,72,77,78,81 54,65 56 81 56 54 56 44 21,49,52,54,56,68,72,81 56 21,44,49,54,56,60,72,81 56 56 56 54 49 49 49,54 54 54, 72 81 49,54,56
Propanoates Methyl propanoate Ethyl propanoate Ethyl-2-propenoate Propyl propanoate
56 24,25,27,46,49,54,56,66 54 25,27,32,33,34,38,56
263
5. PEAR FRUIT VOLATILES
Butyl propanoate Hexyl propanoate Ethyl-2-methyl propanoate Ethyl-2-methyl propenoate 3-Methylbutyl-2-methylpropanoate 1-Methylbutyl-2-methyl propanoate Pentyl-2-methylpropanoate Hexyl-2-methylpropanoate 2-Methylhexyl propanoate Butanoates Methyl butanoate Methy1-iso-butanoate Methy1-4-oxytransbutenoate Ethyl butanoate Ethyl-iso-butanoate Ethyl-2-butenoate Ethyl-(E)-2-butenoate Methyl-2-methylbutanoate Ethyl-4-oxytransbutenoate Ethyl-3-hydroxybutanoate Ethyl-3-acetoxybutanoate Propyl butanoate Ethyl-2-methyl butanoate Ethyl-(E)-2-methyl-2-butenoate Butyl butanoate Butyl-iso-butanoate iso-Butyl-iso-butanoate 1-Methylpropyl butanoate 2-Methylpropyl butanoate Propyl-2-methyl butanoate Methyl-2-ethyl-2-methyl butanoate Pentyl butanoate Butyl-2-methyl butanoate Hexyl butanoate Hexyl-iso-butanoate Hexyl-2-butenoate 3-Methylbutyl-3-methyl butanoate Heptyl butanoate
56,81 49,56,78,81 49,54 54 56 56 56 56 56 49,54,56,81 27 21 27,45,47,49,54,56,66,81 25 49 54 49 21 54 54 49,56,81 49,54,56,66 54 49,56,72,78,81 25 27 56 49,81 56 68 56 56,81 49,54,56,72,78,81 81 56 56 56 (continues)
264 Table 5.2.
F. RAPPARINI AND S. PREDIERI (continued)
Compounds
References (Table 5.1 code)
1-Methylhexyl butanoate Hexyl-2-methyl butanoate Octyl butanoate Butyl-(E)-2-methylbutyl-2-enoate
56 49,56,81 49,68 44
Pentanoates Methyl pentanoate 3-Methyl pentanoate Ethyl pentanoate Butyl pentanoate Hexyl pentanoate 3-Methyl fluorine pentanoate
49 66 47,49,54 81 81 66
Hexanoates Methyl hexanoate Ethyl hexanoate Ethyl-(E)-2-hexenoate Ethy1-(E)-3-hexenoate Ethyl-(Z)-3-hexenoate Ethyl-3-hydroxyhexanoate Propyl hexanoate 1-Methylethyl hexanoate Butyl hexanoate Butyl-2-hexenoate Butyl-3-hexenoate Butyl-4-hexenoate 2-Methylpropyl hexanoate Pentyl hexanoate 2-Methylbutyl hexanoate Hexyl hexanoate
49,54,56,81 44,47,49,52,54,56,66,68,72,81 49,54 54 54 49,54,66 49,56,81 56 49,56,60,72,78,81 56 56 56 49,56 49,56,81 56 49,56,72,78,81
Heptanoates Methyl heptanoate Ethyl heptanoate
49,56 49,54,56
Octanoates Methyl octanoate Methyl-(E)-2-octenoate Methyl-(Z)-3-octenoate Methyl-3-hydroxyoctanoate Ethyloctanoate Ethyl-(E)-4-octenoate
21,49,56,72,81 21,49,56,65 56,65 21,44,57,65 18,21,49,54,56,65,66,72,81 49
Z65
5. PEAR FRUIT VOLATILES Ethyl-(E)-Z-octenoate Ethyl-(Z)-Z-octenoate Ethyl-(Z)-3-octenoate Ethyl-3-hydroxyoctanoate Ethyl-5-(Z)-3-hydroxyoctenoate Ethyl-3-acetoxyoctanoate Propyl octanoate Butyl octanoate Z-Methylpropyl octanoate 3-Methylbutyl octanoate
21,45,49,54,56,65 56 65 Zl,44,45,54,57,65 57 65 49,56
Hexyl octanoate
56 49 49 49,56
Nonanoates Ethyl nonanoate
49,56
Decanoates Methyl decanoate Methyl-(E)-Z-decanoate Methy1-4-decanoate Methy1-(Z)-4-decanoate Methyl-(Z)-?-decanoate Methyl decenoate Methyl-Z-decenoate Methyl-4-decenoate Methyl-(E)-Z-decenoate Methyl-(Z)-?-decenoate Methyl-(Z)-4-decenoate Ethyl decanoate Ethyl-(Z)-4-decanoate Ethyl decenoate Ethyl-4-decenoate EthyI-(E)- Z-decenoate Ethy1-(E)-3-decenoate Ethy1-(Z)-4-decenoate Methyl- Z,4-decadienoate Methyl-(E,Z)-Z ,4-decadienoate Methyl-(E,E)-Z,4-decadienoate Methyl-(Z,Z)-Z,4-decadienoate Ethyl-2,4-decadienoate Ethyl-(E,Z)-Z,4-decadienoate Ethy I-(E,E)- Z,4-decadienoate Ethyl-(Z,Z)-Z ,4-decadienoate Propyl-(E,Z)-Z,4-decadienoate Butyl-(E,Z)-Z,4-decadienoate
34 56 Z2 34 7Z 56 56 21,38,56,65 3Z 21,3Z,33,38,44,46,49,65,81 21,ZZ,3Z,33,34,38,44,49,54,56,65,66,72,81 34 38 56 Zl,33,44,56,65,81 49 21, ZZ, 32, 33,38,44,45,46,49, 54, 81 49 16,Zl,Z2,3Z,33,34,38,44,46,56,65,7Z,81 Zl,ZZ,32,33,34,38,44,46,56 56 49 17,Zl,ZZ,44,45,46,49,54,56,65,72 21,ZZ,32,33,34,38,44,46,54,56 56 65,Z8 65,Z8
Zl,Z2,49, 56,65, 7Z,81
(continues)
266
Table 5.2.
F. RAPPARINI AND S. PREDIERI (continued)
Compounds
References (Table 5.1 code)
Hexyl-(E,E)-2,4-decadienoate Hexy1-(E,Z)-2 ,4-decadienoate Ethyl decatrienoate Ethyl-(E,E,Z)-2,4,7-decatrienoate Ethyl-(E,Z,Z)-2,4, 7-decatrienoate
28 65,28 49 28,56 65
Other esters C 12-CI8 Ethyl dodecanoate 2,4,6-trimethyl dodecanoate Methyl-(E)-2-dodecenoate Ethyl-ll-dodecenoate Ethyl-(?)-dodecenoate Ethyl-(E)-2-dodecenoate Ethyl dodecadienoate Methyl-(E,Z)-2,6-dodecadienoate Ethyl-(E,Z)-2,6-dodecadienoate
49 66 28 65 56 28 28 28 28
Ethyl-(E,Z,Z)-2,6,9-
dodecatrienoate Methyl tetradecanoate Ethyl tetradecanoate Methyl-(?)-tetradecenoate Methyl-(Z)-5-tetradecenoate Ethyl-(?)-tetradecenoate Ethy1-(Z)-5-tetradecenoate Methyl-(Z,Z)-5,8-tetradecadienoate Ethyl-(Z,Z)-5,8-tetradecadienoate Methyl-(E,E,Z)-2,4,8-tetradecatrienoate Eth yl-(E,E,Z)- 2,4 ,8-tetradecatrienoate Methyl hexadecanoate Ethyl hexadecanoate Methyl hexadecenoate Methyl-(Z)-7-hexadecenoate Ethyl hexadecenoate Methyl hexadecadienoate Methyloctadecanoate Methyl-(Z)-9-octadecenoate Methyl-l0-octadecenoate
28 56 28,49,56 56 28 56 28,65 28,56,65 28,45,56,65 28 28 28, 76 28,49,66,76 28 56 28 56 28 28 56
267
5. PEAR FRUIT VOLATILES Methyl-2,4-octadienoate Ethyl-2,4-octadienoate Methyl-2,4,6-octatrienoate Dibutyl phthalate Diethyl carbonate Ethyl benzoate Butyl benzoate Hexyl benzoate Ethyl tiglate Methyllinoleate Methyllinolenate Ethyllinolenate Methyl oleate Hydrocarbons Methyl benzene (toluene) Dimethyl benzene (xylene) n-Undecane n-Pentadecane n-Hexadecane n-Heptadecane n-Octadecane n-Nonadecane n-Methylnaphtalene Valencene Undecatetraene 1-(E,Z)-3,5-Undecatriene 4-Methyl cyclohexene 1-Methyl-4-(1-methylethyl)1,3-cyclohexadiene Benzeneacetonitrile 4-Allylanisole (estragole) 4-Propenylanisole (anethole) Tributylmethyl borane Terpenes Limonene ~-Phellandrene
3-Carene a-Farnesene (Z)-a-Farnesene (E,E)-a-Farnesene (E,Z)-a- Farnesene (E,E)-3 ,6-a-Farnesene
56 56 56 44 54 47,49,54 56 56 49 45, 76 45, 76 76 45 44,47 47 44,81 47,49,66 49 47,49,66 49 47,49 49 49 72 41 81 56 81 60,81 81 66 44,52,54,60 56 56 31,42,44,45,47,49,50,52,54,58,60,69,74,76,78 44 56,72,81 56,72,81 65 (continues)
268 Table 5.2.
F. RAPPARINI AND S. PREDIERI (continued)
Compounds
References (Table 5.1 code)
Copaene (E)-Linalool oxide (Z)-Linalooloxide a-Terpineol Terpinen-4-o1 (E,E)- Farnesol (E,E)-3 ,6-Farnesol Eugenol
72 65 65,81 44,49,54 44,54 44 65 49,68
Acids Acetic acid 2-Methyl butanoic acid 3-Methyl butanoic acid Hexanoic acid Nonanoic acid Hexadecanoic acid
54,72 65 65 54 72 44
Sulphur compounds Ethylmethylthio acetate Ethyl-3-methylthio propanoate 3-Methylthiopropyl acetate Ethyl-3-methylthio-(E)2-propenoate Ethyl-3-methylthio-(Z)2-propenoate 3-Methylthio-propanal (methional)
54 49,54,65 49,54 49,54 54 65
Miscellaneous ~-Damascenone
3,4-Dehydro-~-ionol
2-Ethyl furan Pentyl furan Biphenyl 2-Methoxy-3-iso-propyl pyrazine Diethyl phosphine 3-Hepta alkyne-2,6-diketone5-methyl-5-(1-methyl ester) 1-Methyl-4-(1-methylethylidene)-cyclohexane 1,3-Dioxanes
65 65 81 47,60 49 60 66 66 56 57
5. PEAR FRUIT VOLATILES
269
The relatively good separation obtained by GC has obviated the application of high pressure liquid chromatography (HPLC) in studies of fruit volatiles, although HPLC is normally applied for the separation of nonvolatile compounds. The direct use of HPLC as a prefractionation technique for pear volatiles has been undertaken only sporadically (Russell et al. 1981; Quamme 1984; Zoffoli et al. 1998). The use of HPLC in isolation of fruit volatiles is not useful for the total analysis of the complex mixture of pear volatiles, but has proven to be a ready tool to identify and quantify some important volatile compounds of pear aroma, such as decadienoates (Russell et al. 1981; Quamme 1984), a-farnesene, and conjugated trienes (Zoffoli et al. 1998). Indeed, these compounds are characterized by a relatively high degree of unsaturation (Crombie 1955), and thus can be spectrophotometrically detected and quantified by HPLC with an UV detector between 200 and 300 nm (Jennings and Creveling 1963; Heinz et al. 1964; Heinz et al. 1966; Creveling and Jennings 1970; Quamme and Marriage 1977; Chen et al. 1990; Chen et al. 1993). HPLC, in contrast to GC, prevents thermal generation of artifacts (Kubeczka 1981). The identification of pear volatiles separated by gas chromatography has been mainly achieved by using their chromatographic retention indices. The Kovats Retention Index (RI) system (Kovats 1965), has been often used for the identification of a large number of volatiles (Jennings and Shibamoto 1980) including those released from pear fruit (Russell et al. 1981; Takeoka et al. 1992; Avelar et al. 1994; Suwanagul and Richardson 1998b). However, Kovats RI alone is not definitive because ofthe possibility of compounds exhibiting the same retention on a given column under a given set of chromatographic conditions. Farkas et al. (1994) published a study useful for the adjustment of operational conditions, enabling high reproducibility of standard relative retention indices for flavor compounds. Kovats RI is generally used as a complementary criterion to reinforce identification determined by spectroscopic techniques such as mass spectrometry (MS). Mass spectral fragmentation pattern is highly characteristic and, when coupled with Kovats RI, provides a powerful tool for compounds identification. Jennings and Shibamoto (1980) have compiled the mass spectra of about 700 aroma volatiles including some found in pear. The GC-MS combination is by far the most applied technique for structural elucidation and reliable identification of aromatic volatile compounds in food and beverages (Maarse 1991), including pears (Shiota 1990; Rizzolo et al. 1991; Horvat et al. 1992; Takeoka et al. 1992; Kjaersgaard et al. 1997; Giintert et al. 1998; Chervin et al. 2000; Oshita et al. 2000; Lo Scalzo et al. 2002; Rapparini and Predieri 2002). Elucidation and confirmation of pear aroma compounds have also utilized nuclear magnetic resonance (NMR) and UV and IR spectroscopic
270
F. RAPPARINI AND S. PREDIERI
methods. On the basis of gas chromatographic studies, and on infrared and ultraviolet spectroscopy, Jennings (1961) and Jennings and Creveling (1963) isolated and characterized several alcohols and acids from freshly prepared essence hydrolysates of 'Bartlett' pear esters. Further studies identified (sometimes tentatively) a few of the major volatile compounds of 'Bartlett' pear by using repetitive gas chromatography, infrared, ultraviolet and mass spectroscopy, nuclear magnetic resonance, and melting points (Jennings and Sevenants 1964; Jennings et al. 1964; Heinz and Jennings 1966; Creveling and Jennings 1970). More recently Giintert et al. (1998) applied the same spectroscopic techniques to identify volatile compounds isolated from pear fruits. The use of simple procedures such as acidic or alkaline extraction, hydrolysis, formation of intensely coloured derivatives, hydrogenation, or ozonolysis, as separation techniques prior to gas chromatographic analysis provided additional information on the chemical classes involved (Luh et al. 1955; Jennings 1961; Jennings et al. 1964; Heinz and Jennings 1966; Giannone and Baldrati 1967; Gasca et al. 1969; Creveling and Jennings 1970). Many important volatiles of pear aroma are enantiomeric and in many cases their biosynthesis is stereoselective (Kim and Grosch 1978; Kim and Grosch 1981; Gargouri and Legoy 1998). Determination of the enantiomeric composition of volatile compounds could provide important insights into their biosynthesis. There has been great progress in the stereochemical analysis of enantiomers due to the introduction of modified chiral capillary columns (especially cyclodextrins) and multidimensional gas chromatography (MD-GC). These methods provide useful information not only for achieving a better and accurate characterization of volatiles, but also for gaining a deeper insight into their biosynthetic origins. Only few authors have applied these methodologies to identify some volatiles in pear fruits (Takeoka et al. 1992; Beuerle and Schwab 1997b). Quantification of the identified pear volatiles has been mainly performed by calculating the peak area in the chromatogram obtained with a flame ionization detector (FID) (Romani and Ku 1966; Phan-Chon-Ton 1968; Giannone and Baldrati 1967; Jennings and Tressl1974; Russell et al. 1981; Romani et al. 1983; Shiota 1990; Horvat et al. 1992; Avelar et al. 1994; Imayoshi et al. 1995; Beuerle and Schwab 1997a; Kjaersgaard et al. 1997; Lange 1997; Suwanagul and Richardson 1998b; Chervin et al. 2000; Ju and Curry 2000; Ju et al. 2001). In most cases, the quantification was approximate because no FID response was determined, and only in recent years more accurate measurements have been performed. Quantitative analysis has been performed primarily by using different internal standard methods (Heinz et al. 1965; Jennings and Tress11974; Shiota 1990; Rizzolo et al. 1991; Kjaersgaard et al. 1997; Lange et al. 1997; Suwanagul and Richardson 1998b; Chervin et al. 2000) and/or by using standards
5. PEAR FRUIT VOLATILES
271
(Rizzolo et al. 1991; Avelar et al. 1994; Richardson and Kosittrakun 1995; Park et al. 1999; Ju et al. 2001; Pinto et al. 2001; Rapparini and Predieri 2002). A stable isotope-labeled analogue of the analyte is the most accurate internal standard method when a MS detection system is used (Grosch and Schieberle 1988; Butrym and Hartman 1999). Regardless of the method used, collection and analysis of accurate, truly representative volatile samples is difficult. Extraction and concentration are usually prerequisites to the actual analysis of the volatiles themselves and are difficult procedures compared to chromatographic analysis of the volatile extract (Taylor and Linforth 1994). An important factor in properly interpreting any chromatogram is to understand how the flavor volatiles were concentrated and delivered into the instrument. Therefore, a combined utilization of techniques that have differing chemical affinities for pear volatiles is advisable (Paillard et al. 1970; Rizzolo 1988). Volatile emission from pear fruits has also been studied by laserbased spectroscopic techniques, which utilize changes in physical properties of volatiles. De Vries and coworkers (1997) showed that a laser photoacoustic system can be used to detect and monitor minute changes in concentrations of some low-boiling point volatile compounds emitted by pears, such as ethanol and acetaldehyde. Kharlamov and Burrows (2001a,b) applied the laser photoluminescence spectroscopy, based on the ability of organic volatiles emitted by fruit to luminescence when irradiated by the laser beam. They observed qualitative and quantitative changes of the photoluminescence spectrum during fruit ripening. These nonintrusive techniques could provide a real-time monitoring system of volatiles emitted by fruit. Among the nondestructive assessments of volatiles present in the headspace over a fruit sample, electronic odor detection systems, called "electronic noses," which are based on new chemical sensors, are increasingly being applied (Craven et al. 1996; Abbott et al. 1997). These instruments, utilizing differences in the electrochemical properties of volatiles, are based on the adsorption and subsequent desorption of the compounds released by the sample onto an array of semi-conducting polymer or metaloxide sensors, each characterized by its own degree of reactivity and selectivity (Oshita et al. 1998; Sinesio et al. 2000). This system could be more sensitive and simpler than headspace/GC analysis (Oshita et al. 2000; Young et al. 1999), and find application for discriminating one sample from another based on classes of volatiles, rather than for identification/quantification of individual substances (Maul et al. 1998). Several authors tested electronic noses on different fruits such as strawberry, blueberry, peach, melon, tomato, and apple (Hetzroni et al. 1994; Benady et al. 1995; Simon et al. 1996; Maul et al. 1998;
272
F. RAPPARINI AND S. PREDIERI
Brezmes et al. 2000; Sinesio et al. 2000; Di Natale et al. 2001) as well as on pears (Oshita et al. 1998, 2000; Brezmes et al. 2000). Sinesio et al. (2000) found qualitative similarities between the response of an electronic nose system and human sensory measurements in the evaluation of volatiles released by tomato. Oshita et al. (1998, 2000) suggested a strong relationship between the results obtained in pear by headspace GC and the electronic odor detection system used. The electronic nose has been evaluated for nondestructive monitoring of pear fruit ripening process, showing the ability of discriminating fruit of different ripening stages (Oshita et al. 1998, 2000; Brezmes et al. 2000). The low capacity of discriminating odorant molecules, together with the variability due to environmental factors, such as temperature and humidity, limit the application of this technology (Craven et al. 1996). However, if improved, and properly applied, the electronic nose may become a nondestructive technique for monitoring the physiological state (ripening and deterioration) of fruit as well as to replace or supplement classical quality control practice in food chemistry and industry (Oshita et al. 2000; Young et al. 1999; Bremzes et al. 2000). D. Determination of Organoleptic Value of the Identified Volatiles A comprehensive characterization of the volatile profile of fruit includes qualitative and quantitative chemical analysis, together with studies on sensory evaluation of the identified compounds. Chemical data alone does not provide an indication of the relative contribution of the volatiles to the overall aroma in terms of sensorial intensity. Rouseff and Leahy (1995) stress how the most difficult problem is to interpret which combination of components in what proportion is responsible for the perceived aroma. Many of the volatile components are not flavor-active, and other compounds present even in trace amounts can have significant effects (Teranishi et al. 1981). The olfactory system is extremely sensitive; it can detect odors in parts per trillion whereas receptors on the tongue can detect flavors compounds in parts per hundred (Baldwin et al. 2000). Scientific use of human perception and description ability is the basis for a fruitful correlation with analytical data. Chemical, biochemical, and physical interactions of the food constituents occur in the mouth or nose and together with psychological factors, affect perception and evaluation. These interactions make the relationship between instrumental and sensory data intrinsically incomplete (PIotto 1998a; Buettner and Schieberle 2000). Various studies conducted on pear investigated the correlation between chromatographic results and perceived aroma, and led to the
5. PEAR FRUIT VOLATILES
273
identification of pear character impact and contributory compounds. Jennings et al. (1960) showed that after fractionating aqueous essences of processed pears, five fractions contributed significantly to the desirable pear aroma, while four possessed undesirable aromas. Hexyl acetate was reported to be a contributory flavor compound, and methyl-(E,Z)2,4-decadienoate a "character impact compound" for 'Bartlett' pears. Subsequently, also ethyl-(E,Z)-2,4-decadienoate was recognized as a flavor constituent of 'Bartlett' pear aroma and it was shown that the odors of the pure synthetic methyl, ethyl, propyl, butyl, pentyl, and hexyl esters of (E,Z)-2,4-decadienoic acid are described by sensory panelists as possessing powerful pear aromas. The aroma intensity of 'Bartlett' pear essence, as determined by sensory evaluation, correlates very closely with the intensity of absorbance at 263 to 267 nm, which is associated with esters of 2,4-decadienoic acid (Heinz et al. 1964). Studies performed on processed fruits of several pear cultivars show that high concentrations of decadienoate esters are characteristic of 'Bartlett' pear and other cultivars with 'Bartlett'-like flavor (Quamme and Marriage 1977; Quamme 1984). Suwanagul (1996) combined pear flavor intensity evaluation and volatile emission quantification by SPME on 'Bartlett,' 'Doyenne du Cornice,' and 'Anjou' pears. Pear flavor intensity score, was found to have extremely high positive correlations to the release rates of various esters. On the other hand, highly significant negative correlations were observed between pear flavor intensity and the concentration of a compound with a mild oxidized or cooked note (methyl-(E)- 2-octenoate) and two isomers of a-farnesene. The study of odor intensity of pear volatiles has also been approached by means of calculated threshold values of single identified compounds. A known concentration of the aromatic compound is diluted with a neutral agent (Le., water or air) until the detection limit for human sense is reached (Rothe 1988). This threshold value indicates the minimum concentration needed to produce an olfactory response. It is negatively correlated to aroma intensity of volatile compounds, so it can be used as an index of sensory impact. The most frequently reported method consists of calculating the ratio of each single compound concentration to its odor threshold value. Compounds in excess of their threshold value are considered to make contributions to flavor, whereas those below their threshold are thought to have little or no effect. This parameter has been referred to as "aroma value" (Rothe and Thomas 1963), "unit flavor base" (Keith and Powers 1968), "odor unit" (Do) (Teranishi et al. 1991), and "Odor Activity Value" (OAV) (van Gernert 1994). Guadagni et al. (1966), Buttery et al. (1987), Teranishi et al. (1991), and PIotto et al. (1998b) attempted to calculate the odor unit of volatile compounds in
274
F. RAPPARINI AND S. PREDIERI
different food samples. Based on the Uo values Takeoka et al. (1992) found the following compounds to be important in the Asian pear 'Seuri' (P. pyrifolia [Burm.] Nak.) aroma: ethyl 2-methyl butanoate, ethyl hexanoate, ethyl butanoate, ethyl 2-methyl propanoate, hexyl acetate, ethyl heptanoate, hexanal, ethyl pentanoate, and ethyl propanoate. Ethyl(E,Z)-2,4-decadienoate was a relatively small contributor to the aroma of'Seuri' fruit, conversely to what was observed in 'Bartlett' by Jennings and Sevenants (1964). Another method to evaluate the odor significance of individual compounds and to estimate their relative contribution to overall fruit aroma is gas chromatography-olfactometry (GCO). In this method, the effluent of the GC column is split, with one portion of the eluted volatiles flowing to the instrumental detector (generally FID), whereas the remaining effluent is directed to a "sniff port" where individual peaks are tested by a human assessor (Rothe 1988). Volatile compounds are smelled at the exact time they enter the GC detector, and the assessor rates their odor intensity and defines sensory attributes. The GCO technique has been applied in flavor research to identify odor-active compounds in flavor extracts, to describe odor quality of aroma components, and to quantify the odor significance of a compound in flavor systems (da Silva et al. 1994). Advantages and disadvantages of this technique and its different applications have been widely discussed (Acree 1993; Grosch 1993; Acree and Barnard 1994; van Gernert 1994). GC sniffing studies performed by Berger (1991) and Suwanagul (1996) on 'Bartlett' fruits confirmed the odor impact of hexyl acetate and decadienoates (Heinz et al. 1964; Jennings and Sevenants 1964; Jennings et al. 1964), and several other compounds described as having "pear-like" or "fruity" aroma were also identified. Using the GCO, Suwanagul (1996) identified in 'Doyenne du Cornice' and 'Anjou' nine pear-like aroma compounds identical to those found in 'Bartlett,' plus a number of contributory flavor compounds exhibiting slight differences among the three pear cultivars. The efficiency of GCO was highlighted by Rizzolo (1998), who analyzed the odor profile of 'Doyenne du Cornice' using GC/FID, GC/PID (photoionizator detector) and GCO. Of these methods, only GCO detected a compound present at very low concentration that the author indicates as the one responsible for the characteristic aroma ofthis cultivar and tentatively identifies by GC/MS as methyl-2-ethyl-2-methyl butanoate. The use of GCO without the quantification of the assessor response is limited to screening odor active volatiles in a complex sample (PIotto et al. 1998b). A number of applications combine GCO technique with methods able to determine the odor intensity of the chromatographic resolved compounds (Maarse and van der Heij 1994). The most widely used are CharmAnalysis™ (Acree et al. 1984), aromatic extract dilution analysis
5. PEAR FRUIT VOLATILES
275
(AEDA) (Grosch 1994), and asme (the Greek word for smell) (da Silva et al. 1994). CharmAnalysis™ and AEDA are based on dilution techniques and on the determination of the odor-detection threshold values of the compounds eluted from theGC column. Both methods, as odor units, have been criticized because they assume additivity of odor-active chemicals and do not consider synergism or antagonism between compounds (Forss 1981). These techniques also assume a linear correlation between odor activity (sensory perception) and component concentration, ignoring the exponential relationship between these two variables as postulated by Stevens' law (Frijters 1978; Buttner et al. 1999). The asme method, on the other hand, is based on psychophysical estimation of the individual odor intensity of volatiles according to Stevens' law (da Silva et al. 1994). With asme, trained subjects, sniffing the GC effluent mixed with humidified air, directly record the odor quality, intensity and duration of each odoractive compound. Some applications of CharmAnalysis™ (Cunningham et al. 1986; Young et al. 1996) have already been reported in studies on apple volatiles. asme has been successfully applied in the identification of odor-active compounds emitted by fruits of apple cultivar 'Gala' (PIotto 1998a; PIotto et al. 1998b; PIotto et al. 2000). E. Volatiles Found in Pears
Volatiles emitted by pear fruits are primarily esters, alcohols, hydrocarbons, and aldehydes, and many are high molecular weights (Table 5.2). Unsaturated aliphatic compounds are the primary contributors to pear aroma (Paillard 1990). Aliphatic esters are qualitatively and quantitatively the dominant compounds in pear profiles, as in most fruits (Paillard 1990; Sanz et al. 1997). Jennings and Creveling (1963) found that the disappearance of ester compounds from the alkaline hydrolysate of pear essence resulted in the disappearance of desirable pear aroma. Suwanagul (1996) reported that all odor-active compounds identified by SPME sampling of 'Bartlett,' 'Doyenne du Cornice,' and 'Anjou' were esters. When various European cultivars were studied, esters accounted for as little as 60 percent to as high as 99 percent by dynamic headspace analysis (Suwanagul and Richardson 1998b; Rapparini and Predieri 2002). Similar results were obtained in the Asian pear' Seuri,' characterized by a volatile profile dominated by esters, accounting for 66 percent to 97 percent of the headspace vapors (Takeoka et al. 1992). Pear volatiles typically comprise a wide variety of esters, and those formed from even-numbered carboxy chains such as acetic, butanoic, hexanoic, octanoic, decanoic acid, or dodecanoic acid, and ethyl, butyl, or hexyl alcohol, are more typical than esters containing odd-numbered
276
F. RAPPARINI AND S. PREDIERI
chains. Acetate and butanoate esters are the most prevalent volatile compounds in pears. In some European pears, butyl acetate and hexyl acetate are the major acetate esters (Shiota 1990; Rapparini and Predieri 2002), while in Asian pear 'Ya Li' (P. x bretschneideri Redh.) acetate esters are minor components. Furthermore, esterified fatty acids with up to C18 are widely present in European pear aroma profiles, and are saturated and unsaturated with two, or even three, double bonds. The methyl to hexyl esters of (E,Z)-2,4-decadienoic acid are character-impact compounds of 'Bartlett' pear, and other esters (Jennings and Sevenants 1964) including hexyl acetate, 2-methylpropyl acetate, butyl acetate, butyl butanoate, pentyl acetate, and ethyl hexanoate contribute to pear aroma. All these compounds possess a strong "pear-like" aroma (Suwanagul 1996). Additional compounds, ethyl octanoate and ethyl-(E)-2octenoate, contribute to floral, sweet, or fruity aromas (Table 5.3). Table 5.3.
Odor characterization of some volatiles identified from pear fruits.
Compounds Alcohols n-Propanol n-Butanol n-Pentanol (amyl alcohol) 2-Methyl-l-butanol 3-Methyl-3-buten-2-ol n-Hexanol
Odor descriptions
(E)-2-Hexen-l-ol n-Heptanol n-Octanol
Oxidized pear,4 aldehyde 4 Medicinal,5 metallic 7 Roasted 7 Shunky,5 fresh cheese 7 Leafy/ green 7 Oxidized,4 soapy,4 fresh rose,6 fresh grass,6 engine 7 Urinous 7 Potato pee14 Earthy,6 citrus-like 7
Aldehydes Hexanal (E)-2-Hexenal (E)-2-Heptenal 2-Methyl-2-pentenal
Fruity 7 Seasoned cheese 7 B uggy 7 Green,! sharp 7
Ketones 2-Pentanone (methylpropyl ketone) 2-Heptanone 2-Methylcyclopentanone
FloraF Spicy 7 Butter-like 7
Esters Propyl acetate Butyl acetate
Floral,4 estery4 Fruity,3,4,5,6 very fruity,3 estery,4,6 pear,5,6 flora1,5 sweet,5,6 bubble gum,5 very perfume,5 geranium-like 7
277
5. PEAR FRUIT VOLATILES iso-Propyl acetate Pentyl acetate (amyl acetate) iso-Butyl acetate (2-methylpropyl acetate) iso-Pentyl acetate (3-methylbutyl acetate; iso-amyl acetate) Hexyl acetate 4-Hexen-1-01 acetate Heptyl acetate Octyl acetate 4-0cten-1-01 acetate 2-Phenylethyl acetate Ethyl propanoate Ethyl butanoate Ethyl-2-methyl butanoate Butyl butanoate 1-Methylpropyl butanoate 3-Methylbutyl-3-methyl butanoate Ethyl hexanoate Butyl hexanoate 2-Methylpropyl hexanoate Pentyl hexanoate Hexyl hexanoate Methyl-(EJ-2-octenoate Ethyl octanoate Ethyl-(E)-2-octenoate Ethy1-(Z)-3-octenoate Methy1-4-decenoate Ethyl decanoate Ethyl-4-decenoate Ethyl-(Z)-4-decenoate Methyl-(E,Z)-2,4-decadienoate EthYl-(E,Z)-2,4-decadienoate Ethyl-(E,E)-2,4-decadienoate Ethyl-(Z,Z)-2,4-decadienoate Propyl-(E,Z)-2,4-decadienoate Butyl-(E,Z)-2,4-decadienoate Ethyl-2,4-octadienoate Methyl-2,4,6-octatrienoate 1-(E,Z)-3,5-undecatriene
Pear,4,5,6 fruity,4 estery,4.6 sweet,5 candy,6 floral,6 rancid 7 Pear,4 apple,4 fruity,4 bubble gum,5 sweet,5 floral,6 mushroom 7 Candy,4,5 perfume 4,5,6 Pear,:J,4,5,6 floral,4 sweet,4,5 fruity,6 very fruity,4 estery, 6 clove-like 7 Mushroom4,5,6 Fermented 7 Chemical4, solvent-like 4, rancid perfume 6 Perfume,4,6 candy,5 sweet 5 Sweet,5 cand y 5 Fruity,4 caramel,4 milky4 Fruity,4,5,6 very fruity,3 estery,4 floral,5,6 cand y 5 Fruity,5 sweet,5 cand y 5 Pear,4 estery4 Bubble gum,4 candy4 Bubble gum,4 candy,4 sweet,4 floral 4 Pear,4,5 floral,4 fruity,4,5 estery,4 sweet,5 cooked pear,6 oxidized,6 medicine,6 legume 7 Cooked artichoke 6 Mushroom 4 Lemon,6 citrus,6 green (citrus-lea£)6 Floral,4,5,6 candy 6 Oxidized,4 cooked fruit 4 Floral,4,6 sweet,4 cooked apple,5 fruit y 6 Flora1,6 pear:J Fruity,4,5 sweet 5 Anise 6 Fermented food 4 Citrus 5 pear:J Floral,4 estery,4 pear,3,5 fruity,5 ripe pear,6 very fruit y 6 Pear,1,3,4 pear peel,4 green,4,5 cooked pear fruit,5 ripe pear,6 pear blend,6 fruit y 6 Alcohol,4,6 fermented food,4,5,6 sourS Pear,4,6 fruit y4,6 Pearl Pearl Mushroom4 Perfume 5 Balsamic,2 strong fruit y 2
1, Jennings et al. 1964; 2, Berger et al. 1985b; 3, Berger et al. 1991; 4, Suwanagul 1996 ('Bartlett' pear fruits); 5, Suwanagul 1996 ('Cornice' pear fruits); 6, Suwanagul 1996 ('Anjou' pear fruits); 7, Rizzolo 1998
278
F. RAPPARINI AND S. PREDIERI
Alcohols constitute the second largest category of pear volatile compounds. Depending on the cultivar, alcohols account for 1.5 to 14 percent of the total volatiles collected by headspace sampling of pear fruits (Suwanagul and Richardson 1998b; Rapparini and Predieri 2002). Straight-chain aliphatic and saturated alcohols are detected using headspace or distillation methods. Unsaturated C6 alcohols, which have powerful aroma notes, are produced by Asian pears (Imayoshi et al. 1995). Straight-chain saturated aldehydes identified among pear volatiles are generally accompanied by the corresponding alcohols. Numerous authors have identified acetaldehyde and the C6 aldehydes hexanal and (E)-2-hexenal, both generally formed by enzymatic reactions when cellular structures are disrupted and considered responsible for "green" flavor (Drawert et al. 1974; Imayoshi et al. 1995). These aldehydes are major components in solvent extracts from pulp, but not in headspace samples of intact pear fruit (Imayoshi et al. 1995). Acetaldehyde is often considered to be a fermentation product, mostly found when physiological alteration of the fruit occurs, for example under unfavorable storage conditions (Paillard 1990). It is also produced by damage or cutting, and the quantities emitted are proportional to the area of fruit flesh exposed (Paillard 1990). Apart from 3-hydroxy-Z-butanone (acetoin), only a few ketones, mostly straight-chain, have been reported in solvent extracts and headspace samples. Some hydrocarbons, such as benzene, toluene, and xylene can be considered to be pollutants from anthropogenic activities (Kupiszewska and Pilling 1994), and should be viewed with caution as contamination compounds from the environment. Terpenes, which can provide fruity aromas, are mainly represented in pear fruit by limonene and farnesene. Alpha-farnesene has been found to be present in high concentration in Asian pear peel (Shiota et al. 1981) and in 'La France' pear fruits (Shiota 1990), and its (E) isomer has also been indicated as a characteristic compound of Pome fruits (Paillard 1990). Both isomeric forms of this compound were not found to possess any odor characteristics in the GCO tests (Suwanagul 1996). Conjugated trienes, which are considered as oxidation products of the terpene afarnesene, have been isolated in pear fruits by some authors (Chen et al. 1993; Chen and Varga 1997; Zoffoli et al. 1998; Chervin et al. 2000). Among these trienes, a Cl l hydrocarbon, 1-(E,Z)-3,5-undecatriene, which is characterized by a balsamic, pleasant odor with strong fruity undernotes, possesses an ultra-low odor detection threshold and thus may contribute to the overall pear aroma even at low concentrations (Berger et al. 1985a). Several oxygenated terpenoid volatiles, which are important in the flavor of other fruits, have been identified in pears and are mainly repre-
5. PEAR FRUIT VOLATILES
279
sented by monoterpene alcohols, such as a-terpineol, farnesol, and eugenol even their quantities were much lower than those of aliphatic or olefinic alcohols. These monoterpene alcohols are widely used in artificial flavors and fragrances because of their characteristic floral notes (Arctander 1969). Sulphur-containing compounds having unique odor properties such as methyl-3-methylthio-3-propanoate (Berger 1991), have also been identified in pear (Takeoka et al. 1992; Imayoshi et al. 1995; Oshita et al. 1998). Other volatile compounds present in trace amounts and/or in a restricted range of cultivars, and belonging to more infrequent chemical families, should nevertheless be noted. They may play important roles in pear aroma when their odor threshold is low, or when the odor characteristic is distinct from the fruity note imparted by esters (Table 5.4). III. BIOGENESIS
The biogenetic pathways of most of the aromatic components have been described in detail for several fruits such as apple (Yahia 1994; Fellman et al. 2000), tomato (Buttery and Ling 1993; Baldwin et al. 2000), strawberry (Forney et al. 2000b), and banana (Tressl and Drawert 1973), while information for pear is still scarce. European pears, apple, peach, and banana, are typical climacteric fruits. In the preclimacteric stage, ethylene (CzH z) induces biochemical, physical, and chemical changes resulting in increased protein synthesis and changes in enzyme activity (Schreier 1984). These processes lead to an accumulation of metabolites and substrates, such as fatty acids and amino acids, for production of volatiles (Drawert 1974). Furthermore, early in the ripening process, an increase in permeability of cell membranes occurs (Ben-Arie et al. 1979; Brady 1987). This process, that continues through fruit senescence, is characterized by the breakdown of cell wall components and membranes, leading to a loss of compartmentation and an increase in substrates for volatile synthesis (Paliyath and Droillard 1992). During ripening, the metabolism of the fruit changes mainly to catabolic pathways (Tressl and Albrecht 1986), and high molecular weight structures, such as polysaccharides, lipids, proteins, and amino acids, are enzymatically converted to volatile compounds (Schreier 1984; Heath and Reineccius 1986). Extensive studies have demonstrated that the formation of volatiles in various ripening fruits such as pear, apple, and banana is initiated by the climacteric rise in respiration and reaches a maximum during the postclimacteric ripening phase (Heinz et al. 1965; Romani and Ku 1966; Tressl and Jennings 1972; Jennings and Tressl 1974). In 'Bartlett' pears, volatile formation
280
F. RAPPARINI AND S. PREDIERI
Table 5.4.
Odor threshold of some volatiles that have been identified in pear fruits.
Compound
Hexanal
~o
2-Methylpropyl acetate
4.5"·c, 5", 20\ 161
>-\0
3-Hydroxy-2-butanone
Butyl acetate
Odor threshold in water (ppb)
Chemical structure
HO
IO~O
66 b.
>
•
LD WCtPtlon I
1
Mature
leaf
Fig. 6.2. Diagram of the model for the control of transition to flowering in Sin apsis alba involving sucrose and cytokinins. Step 1 (wavy arrow), perception of LD induction by mature leaves; Step 2 (solid arrow), starch mobilization in leaves and stem followed by transport of sucrose in the phloem to both the apical meristem and roots; Step 3 (dashed arrow), transport in the xylem from roots to leaves of zeatin riboside ([9R]Z and isopentenyladenine riboside ([9RliP); Step 4 (dotted arrow), transport in the phloem from leaves to the apical meristem of isopentenyladenine (iP). (From Bernier et al. 1993.)
gesting that sucrose acts as a floral signal. In both S. alba and X. strumarium, the increase in sucrose export preceded the increase in cytokinin concentration in the xylem. In fact, in S. alba, phloem disruption between the mature leaf and root prevented sucrose translocation to the roots and also eliminated the stimulation of cytokinin export
342
R. DARNELL, D. CANTLIFFE, D. KIRSCHBAUM, AND C. CHANDLER
from roots to the apical meristem via the xylem. Increased export of polyamines from the mature leaves, which coincides with the increased export of cytokinin from the roots, may also be related to flower induction in S. alba, since polyamines appear to interact with cytokinins in the control of the cell division cycle (Bernier et aI. 1993). Although not specifically mentioned, Bernier's model implies that under noninductive conditions, various flowering inhibitors (e.g., GAs in strawberry?) are present that prevent changes in the chemical constituents that lead to flowering. Although chemical changes (particularly changes in sucrose and cytokinin) in phloem sap concentration prior to floral induction have been reported in both SD and LD plants, the evidence is insufficient to conclude that these chemicals are floral signals. Verification lies with studies to test the effects of applied sucrose and cytokinins, as well as genetic studies using flowering mutants and transgenic plants. V. GENETICS OF FLORAL INDUCTION
Although several genes involved in fruit development, flavor, and cold tolerance in strawberry have been identified (Hokanson and Maas 2001), identification of genes involved in the flowering process in strawberry has not yet been achieved. However, multiple genes that control flowering in Arabidopsis and pea have been identified. In Arabidopsis, flowering involves the expression of floral meristem identity genes, such as LEAFY (LFY) , APETALA1, and 2 (AP1, AP2), CAULIFLOWER (CAL), and UNIDENTIFIED FLORAL ORGANS (UFO) (Koornneef et aI. 1998; van Nocker 2001). There appear to be at least four pathways that control expression of these genes and therefore flowering in Arabidopsis. Two appear to be regulated developmentally; while two are regulated environmentally (i.e., photoperiod and vernalization). The photoperiodic promotion pathway begins with daylength perception by photoreceptors, such as phytochrome (principally PHYA and PHYB) and cryptochrome (CRYl and CRY2) (Levy and Dean 1998). Daylength perception initiates a transduction or input pathway that apparently entrains the circadian clock, resulting in output pathways that generate overt rhythms, that is, photoperiodic control of flowering (McClung 2001). Components of the downstream signaling pathways from PHY and CRY are unknown, although several intermediates are implicated in an Arabidopsis circadian system model proposed by McClung (2001). Light quality also influences flowering through effects on the circadian clock (van Nocker 2001). However, light is not required for floral induction, since Arabidopsis can be induced to flower in complete darkness when sufficient
6. THE PHYSIOLOGY OF FLOWERING IN STRAWBERRY
343
carbohydrates are provided to the meristem (Koornneef et al. 1998; van Nocker 2001). Vernalization also induces flowering in Arabidopsis, through the expression of vernalization genes (VRNl and VRN2) and a transduction pathway that may involve GA synthesis, activity, or both (Koornneef et al. 1998). However, Arabidopsis mutants defective in GA biosynthesis or perception still exhibit normal flowering responses to vernalization (van Nocker 2001), arguing against the involvement of GA as a component of the transduction pathway. Work with late-flowering ecotypes of Arabidopsis revealed the presence of a dominant allele at the FRIGIDA (FRI) locus that is responsible for delayed flowering (Battey 2000). These effects can be overcome by vernalization. A second locus, FLOWERING LOCUS C (FLC), has been identified that also delays or represses flowering. FLC is hypothesized to be the primary flowering inhibitor in Arabidopsis, whose synthesis is promoted by FRI (Michaels and Amasino 1999), and may be inhibited by VRN2 (Sheldon et al. 1999), although evidence for this is equivocal. The octoploid nature of the commercial strawberry makes genetic analysis of flowering complex, and, as stated earlier, no genes involved in flowering of strawberry have as yet been identified. However, Battey et al. (1998) are using positional cloning to isolate genes involved in flowering of F. vesca. This wild species has both a continually flowering form (F. vesca f. semperflorens) and a seasonal flowering form (F. vesca f. vesca). A single gene controls this trait and the dominant allele confers seasonal flowering in F. vesca f. vesca (Brown and Wareing 1965). This is in contrast to work with F. x ananassa, which suggests that the dominant allele confers photoperiodic insensitivity (Ahmadi et al. 1990) or that flowering in F. x ananassa is a quantitative trait (Hancock et al. 2001) On the other hand, F. vesca has several characteristics that make it an attractive system for studying flowering in strawberry; it is diploid (2n = 14), has a short generation time (approximately four months), a clear distinction between vegetative and reproductive growth, and a described transformation system (EI Mansouri et al. 1996; Battey et al. 1998). Furthermore, the physiology of the flowering processes in F. vesca and F. x ananassa is similar enough to imply a common molecular basis (Battey et al. 1998). Since the data support the hypothesis that floral induction in strawberry occurs after removal or repression of a floral inhibitor, Battey (2000) speculates that a homologue of FLC may be involved in the inhibition of flowering in strawberry and other plants. Under conditions of warm temperatures and long photoperiods, this repressor gene becomes active in SD plants, and floral inhibition occurs (Fig. 6.3). Battey further proposes that expression or activity of the FLC homologue in
R. DARNELL, D. CANTLIFFE, D. KIRSCHBAUM, AND C. CHANDLER
344
Warm, long days
I Cool, short days I t-------
Flower repressor gene active
I Flower :epr~ssor I t------gene InactIve
Cold ----------1 Reactivation of flower repressor-! gene
Inhibitor
II
No inhibitor
Vegetative growth, flower emergence and fruiting
II
Flower initiation
I
Sep
Nov
!~C2r~~S_e~ inhibitor
Dormancy
Jan
Feb
I
Mar
Apr
May
Jun
Jul
Aug
Oct
I t------,Dormancy
Dec
Fig. 6.3. The physiological and genetic control of the perennial cycle in the Junebearing strawberry. (Months applicable in N. Hemisphere.) (From Battey et al. 1998.)
strawberry may be inhibited by homologues of genes identified in Arabidopsis that are involved in the promotive photoperiodic pathway. Thus, under cool temperatures and short photoperiods, the repressor gene is inactivated and floral induction occurs. However, this hypothesis has not been verified. As well, the roles of winter chilling, low temperatures, and other environmental factors in regulating expression of flowering genes in strawberry, how these genes interact, and the components of the signal transduction pathway(s) are still unknown. Work is continuing, however, and recent research using intersimple sequence repeat PCR primer-pair combinations has identified two markers located within 2.2 eM of the seasonality locus inF. vesca (Cekic et al. 2001). This represents the first step toward isolation of the seasonal flowering gene by map-based cloning. VI. CONCLUSIONS
The transition from vegetative to reproductive growth in strawberry involves a series of consecutive stages beginning with floral induction. In general, flower induction in strawberry is controlled primarily by the interaction of photoperiod, temperature, and genotype. The effects of these factors on flowering have been described in many studies, and flowering can be manipulated based on information from such studies. Despite our ability to regulate flowering, the connection between the environmental signals and flower induction has not been elucidated. The evidence supports the idea of the transmission of a floral inhibitor between leaves and apices or between mother and daughter plants, rather than the transmission of a florigenic substance, although the lat-
6. THE PHYSIOLOGY OF FLOWERING IN STRAWBERRY
345
ter theory has not yet been discarded. However, regulation of flowering by a single factor fails to account for the complexities of flowering, which is inducible by a variety of signals. Clearly, the unraveling of the flowering process in strawberry will not be achieved by continuation of descriptive studies on environmental influences on flower induction and development. Rather, it awaits the identification of the genes involved in the flowering process. Both the octoploid nature of the cultivated strawberry and the difficulty in manipulating it in vitro present obstacles to standard molecular biology approaches (Hokanson and Maas 2001). F. vesca, a diploid with similar flowering physiology to F. x ananassa, offers a simpler plant system with which to work. However, genetic analysis of flowering in F. vesca may have limited applicability to the more complex octoploid, F. x ananassa, and the usefulness of this approach in unraveling the flowering process in F. x ananassa remains to be seen. LITERATURE CITED Ahmadi, H., R. S. Bringhurst, and V. Voth. 1990. Modes of inheritance of photoperiodism in Fragaria. J. Am. Soc. Hort. Sci. 115:146-152. Albregts, E. E., and C. M. Howard. 1977. Effect of planting date and plant chilling on growth and fruiting responses of three strawberry clones. Proc. Fla. State Hort. Soc. 90: 278-280.
Albregts, E. E., and C. M. Howard. 1980. Effect of pre-transplant chilling and planting date on the growth and fruiting response of the 'Dover' strawberry. Proc. Fla. State Hart. Soc. 93:239-241.
Avigdori-Avidov, H., E. E. Goldschmidt, and N. Kedar. 1977. Involvement of endogenous gibberellin in the chilling requirements of strawberry (Fragaria x ananassa Duch.). Ann. Bot. 41:927-936. Bailey, J. S., and A. W. Rossi. 1965. Effect offall chilling, forcing temperature, and day length on the growth and flowering of Catskill strawberry plants. Proc. Am. Soc. Hart. Sci. 87: 245-252.
Battey, N. H. 2000. Aspects of seasonality. J. Expt. Bot. 51:1769-1780. Battey, N. H., P. LeMiere, A. Tehranifar, C. Cekic, S. Taylor, K. J. Shrives, P. Hadley, A. J. Greenland, J. Darby, and M. J. Wilkinson. 1998. Genetic and environmental control of flowering in strawberry, p. 111-131. In: K. E. Cockshull, D. Gray, G. B. Seymour, and B. Thomas (eds.). Genetic and environmental manipulation of crops. CAB, New Yark. Bernier, G. 1988. The control of flaral evocation and morphogenesis. Annu. Rev. Plant Physiol. Plant Mol. BioI. 39:175-219. Bernier, G., L. Corbesier, C. Perilleux, A. Havelange, and P. Lejeune. 1998. Physiological analysis ofthe floral transition, p. 103-109. In: K. E. Cockshull, D. Gray, G. B. Seymour, and B. Thomas (eds.). Genetic and environmental manipulation of crops. CAB, New York. Bernier, G., A. Havelange C. Houssa, A. Petitjean, and P. Lejeune. 1993. Physiological signals that induce flowering. Plant Cell 5:1147-1155. Bernier, G., J. M. Kinet, and R. M. Sachs. 1981. The physiology of flowering, Vol. II. CRC Press, Boca Raton, FL.
346
R DARNELL, D. CANTLIFFE, D. KIRSCHBAUM, AND C. CHANDLER
Bish, E. B., D. J. Cantliffe, and C. K. Chandler. 1996. Strawberry plug transplants: regulation of growth and production. Proc. Fla. State Hort. Soc. 109:160-164. Blatt, C. R, and A. G. Sponagle. 1974. Effects of several growth regulators on runner plant production, yield and fruit maturity of the strawberry. Can. J. Plant Sci. 54:873-875. Borthwick, H. A., and M. W. Parker. 1938. Influence of photoperiods upon differentiation of meristems and the blossoming of Biloxi soybeans. Bot. Gaz. 99:825-839. Brown, T., and P. F. Wareing. 1965. The genetic control of the everbearing habit and three other characters in varieties of Fragaria vesca. Euphytica 14:97-112. Cain, N. P., R P. Ormrod, and D. Evans. 1983. Yield responses of strawberry to fall application of ethephon. Can. J. Plant Sci. 63:1093-1095. Cekic, c., N. H. Battey, and M. J. Wilkinson. 2001. The potential ofISSR-PCR primer-pair combinations for genetic linkage analysis using the seasonal flowering locus in Fragaria as a model. Theor. Appl. Genet. 103:540-546. Ceulemans, R, W. Baets, M. Vanderbruggen, and 1. Impens. 1986. Effects of supplemental irradiation with HID lamps, and NFT gutter size on gas exchange, plant morphology and yield of strawberry plants. Scientia Hort. 28:71-83. Chabot, B. F. 1978. Environmental influences on photosynthesis and growth in Fragaria vesca. New Phytol. 80:87-98. Chajlachjan, M. H. 1936. On the hormonal theory of plant development. Compt. Rend. (Doklady) Acad. Sci. U.RS.S. 3:442-447. Chen, W. S. 1991. Changes in cytokinins before and during early flower bud differentiation in lychee (Litchi chinensis Sonn.). Plant Physiol. 96:1203-1206. Chen, W. S., K. L. Huang, and H. C. Yu. 1997. Cytokinins from terminal buds of Euphoria longana during different growth stages. Physiol. Plant. 99:185-189. Choma, M. E., and D. G. Himelrick. 1984. Responses of day-neutral, June-bearing and everbearing strawberry cultivars to gibberellic acid and phthalamide treatments. Scientia Hort. 22:257-264. Darnell, R L., and J. F. Hancock. 1996. Balancing vegetative and reproductive growth in strawberry, p. 144-150. In: M. V. Pritts, C. K. Chandler, and T. E. Crocker (eds.), Proc. IV North American strawberry conference. Univ. of Florida, Gainesville, FL. Darrow, G. M. 1936. Interrelation of temperature and photoperiodism in the production of fruit-buds and runners in the strawberry. Proc. Am. Soc. Hort. Sci. 34:360-363. Darrow, G. M. 1966. The strawberry. Holt, Rinehart and Winston, New York. Deng, X., and F. 1. Woodward. 1998. The growth and yield responses of Fragaria ananassa to elevated CO 2 and N supply. Ann. Bot. 81:67-71. Dennis, F. G. Jr., and H. O. Bennett. 1969. Effect of gibberellic acid and deflowering upon runner and inflorescence development in an everbearing strawberry. J. Am. Soc. Hort. Sci. 94:534-537. Dennis, F. G. Jr., J. Lipecki, and C. Kiang. 1970. Effect of photoperiod and other factors upon flowering and runner development of three strawberry cultivars. J. Am. Soc. Hort. Sci. 95:750-754.
Deyton, D. K, C. K Sams, and J. C. Cummins. 1991. Strawberry growth and photosynthetic responses to padobutrazol. HortScience 26:1178-1180. Downs, R J., and A. A. Piringer. 1955. Differences in photoperiodic responses of everbearing and June-bearing strawberries. Proc. Am. Soc. Hort. Sci. 66:234-236. Durner, E. F., J. A. Barden, D. G. Himelrick, and E. B. Poling. 1984. Photoperiod and temperature effects on flower and runner development in day-neutral, Junebearing, and everbearing strawberries. J. Am. Soc. Hort. Sci. 109:396-400. Durner, E. F., and E. B. Poling. 1987. Flower bud induction, initiation, differentiation, and development in the 'Earliglow' strawberry. Scientia Hort. 31:61-69. Durner, E. F., and E. B. Poling. 1988. Strawberry developmental responses to photoperiod and temperature: a review. Adv. Straw. Prod. 7:6-14.
6. THE PHYSIOLOGY OF FLOWERING IN STRAWBERRY
347
Durner, E. F., E. B. Poling, and E. A. Albregts. 1986. Early season yield responses of selected strawberry cultivars to photoperiod and chilling in a Florida winter production system.]. Am. Soc. Hort. Sci. 111:53-56. El-Antably, H. M., P. F. Wareing, and]. Hillman. 1967. Some physiological responses to D, L abscisin (dormin). Planta 73:74-90. EI Mansouri, I.,]. A. Mercado, V. Valpuesta,]. M. Lopez-Aranda, R. Pliego-Alfaro, and M. A. Quesada. 1996. Shoot regeneration and Agrobacterium-mediated transformation of Fragaria vesca L. Plant Cell Rep. 15:642-646. Esau, K. 1977. Anatomy of seed plants. 2nd ed. Wiley, New York. FAO. 2001. FAOSTAT Agricultural Statistics Database. http://www.fao.org. Ferree, D. c., and E. ]. Stang. 1988. Seasonal plant shading, growth, and fruiting in 'Earliglow' strawberry.]. Am. Soc. Hort. Sci. 113:322-327. Guttridge, C. G. 1956. Photoperiodic promotion of vegetative growth in the cultivated strawberry plant. Nature 178:50-51. Guttridge, C. G. 1959a. Evidence for a flower inhibitor and vegetative growth promoter in the strawberry. Ann. Bot. 23:351-360. Guttridge, C. G. 1959b. Further evidence for a growth-promoting and flower-inhibiting hormone in strawberry. Ann. Bot. 23:613-621. Guttridge, C. G. 1968. Hormone physiology of growth regulators in strawberry, p. 157-169. In: Plant growth regulators, monograph no. 21. Soc. Chern. Ind., London. Guttridge, C. G. 1969. Fragaria, p. 247-267. In: L. T. Evans (ed.). The induction of flowering. Cornell Univ. Press, Ithaca, New York. Guttridge, C. G. 1985. Fragaria x ananassa, p. 16-33. In: A. H. Halevy (ed.). Handbook of flowering. Vol. III. CRC Press, Boca Raton, FL. Guttridge, C. G., and P. A. Thompson. 1959. Effect of gibberellic acid on length and number of epidermal cells in petioles of strawberry. Nature 183:197-198. Guttridge, C. G., and P. A. Thompson. 1964. The effect of gibberellins on growth and flowering of Fragaria and Duchesnea. ]. Expt. Bot. 15:631-646. Hamner, K. c., and]. Bonner. 1938. Photoperiodism in relation to hormones as factors in floral initiation and development. Bot. Gaz. 100:388-431. Hancock,]. F. 1999. Strawberries. CABI, New York. Hancock, ]. F., ]. ]. Luby, A. Dale, A. Callow, S. Serce, and A. EI-Shiek. 2002. Utilizing wild Fragaria virginiana in strawberry cultivar development: Inheritance of photoperiod sensitivity, fruit size, gender, female fertility and disease resistance. Euphytica (in press). Hartmann, H. T. 1947a. Some effects oftemperature and photoperiod on flower formation and runner production in the strawberry. Plant Physiol. 22:407-420. Hartmann, H. T. 1947b. The influence of temperature on the photoperiodic response of several strawberry cultivars grown under controlled environment conditions. Proc. Am. Soc. Hort. Sci. 50:243-245. Hartz, T. K., A. Baameur, and D. B. Holt. 1991. Carbon dioxide enrichment of high-value crops under tunnel culture. ]. Am. Soc. Hort. Sci. 116:970-973. Heide, O. 1977. Photoperiod and temperature interactions in growth and flowering of strawberry. Physiol. Plant. 40:21-26. Hokanson, S. c., and]. L. Maas. 2001. Strawberry biotechnology. Plant Breeding Rev. 21: 139-180. Ito, H., and T. Saito. 1962. Studies on the flower formation in the strawberry plants. I. Effects of temperature and photoperiod on the flower formation. Tahoku]. Agri. Res. 13:191-203. ]ahn, O. L., and M. N. Dana. 1966. Dormancy and growth of the strawberry plant. Proc. Am. Soc. Hort. Sci. 89:322-330. ]onkers, H. 1965. On the flower formation, the dormancy and the early forcing of strawberries. Meded. Landbouwhogesch. Wageningen 65-6:1-59.
348
R. DARNELL, D. CANTLIFFE, D. KIRSCHBAUM, AND C. CHANDLER
Kadman-Zahavi, A., and E. Ephrat. 1974. Opposite response groups of short-day plants to the spectral composition of the main light period and end-of-day red or far red irradiation. Plant Cell Physiol. 15:693-699. Kawakami, T., H. Aoki, and T. Toki. 1990. Method of early fruit maturing using low night temperatures and short day conditions during the propagation of strawberries. Bul. China Pref. Agri. Expt. Sta. 31:55-72 (English summary). Kender, W. J., Carpenter, S., and J. W. Braun. 1971. Runner formation in everbearing strawberry as influenced by growth-promoting and inhibiting substances. Ann. Bot. 35:1045-1052.
Kirschbaum, D. S. 1998. Temperature and growth regulator effects on growth and development of strawberry. MS Thesis, Univ. of Florida, Gainesville, FL. Koornneef, M., C. Alonso-Blanco, A. J. M. Peeters, and W. Soppe. 1998. Genetic control of flowering time in Arabidopsis. Annu. Rev. Plant Physiol. Plant Mol. BioI. 49:345-370. Larson, K. D. 1994. Strawberry, p. 271-297. In: B. Schaffer and P. Andersen (eds.). Handbook of environmental physiology of fruit crops. Vol. I: Temperate crops. CRC Press, Boca Raton, FL. Leshem, Y., and D. Koller. 1964. The control of flowering in the strawberry Fragaria ananassa Duch. I. Interaction of positional and environmental effects. Ann. Bot. 112:569-578. Leshem, Y., and D. Koller. 1966. The control of flowering in the strawberry Fragaria ananassa Duch. II. The role of gibberellins. Ann. Bot. 30:587-595. Levy, Y. Y., and C. Dean. 1998. The transition to flowering. Plant Cell 10:1973-1989. Lopez-Galarza, S., B. Pascual, J. Alargada, and J. Maroto. 1989. The influence of winter gibberellic acid applications on earliness, productivity and other parameters of quality in strawberry (Fragaria x ananassa Duch.) cultivation on the Spanish Mediterranean coast. Acta Hort. 265:217-222. Manakasem, Y., and P. B. Goodwin. 1998. Using the floral status of strawberry plants, as determined by stereomicroscopy and scanning electron microscopy to survey the phenology of commercial crops. J. Am. Soc. Hort. Sci. 123:513-517. McArthur, D. A. J., and G. W. Eaton. 1987. Effect offertilizer, paclobutrazol, and chloromequat on strawberry. J. Am. Soc. Hort. Sci. 112:241-246. McClung, C. R. 2001. Circadian rhythms in plants. Annu. Rev. Plant Physiol. Plant Mol. BioI. 52:139-162. Michaels, S. D., and R. M. Amasino. 1999. FLOWERING LOCUS C encodes a novel MADS domain protein that acts as a repressor of flowering. Plant Cell 11 :949-956. Moore, J. N., and L. F. Hough. 1962. Relationships between auxin levels, time of floral induction and vegetative growth of the strawberry. Proc. Am. Soc. Hort. Sci. 81:255-264. Nicoll, M. F., and G. J. Galletta. 1987. Variation in growth and flowering habits ofJunebearing and everbearing strawberries. J. Am. Soc. Hort. Sci. 112:872-880. Okimura, M., and I. Igarashi. 1997. Effects of photoperiod and temperature on flowering in everbearing strawberry seedlings. Acta Hort. 439:605-607. Piringer, A. A., and D. H. Scott. 1964. Interrelation of photoperiod, chilling, and flower cluster and runner production by strawberries. Proc. Am. Soc. Hort. Sci. 84:295-301. Porlingis, I., and D. Boynton. 1961. Growth responses of the strawberry plant Fragaria chiloensis var. ananassa, to gibberellic acid and to environmental conditions. Proc. Am. Soc. Hort. Sci. 78:261-269. Reid, J. H. 1983. Practical growth regulator effects on strawberry plants-a review. Crop Res. 23:113-120.
6. THE PHYSIOLOGY OF FLOWERING IN STRAWBERRY
349
Sheldon, C. S., J. K Burn, P. P. Perez, J. Metzger, J. A. Edwards, W. J. Peacock, and K S. Dennis. 1999. The FLF MADS box gene: a repressor of flowering in Arabidopsis regulated by vernalization and methylation. Plant Cell 11:445-458. Singh, J. P., G. S. Randhawa, and N. L. Jain. 1960. Response of strawberry to gibberellic acid. Indian J. Hort. 17:21-30. Smeets, L. 1976. Effect of light intensity on stamen development in the strawberry cultivar 'Glasa.' Scientia Hort. 4:255-260. Smith, C. R. 1960. Effect of autumn applications of potassium gibberellate on fruit production of the strawberry. Nature 187:620. Strik, B. C. 1985. Flower bud initiation in strawberry cultivars. Fruit Var. J. 39:5-9. Tafazoli, K, and D. Vince-Prue. 1978. A comparison of the effects of long days and exogenous growth regulators on growth and flowering in strawberry, Fragaria x anon ossa Duch. J. Hort. Sci. 53:255-259. Tarenghi, K, and J. Martin-Tanguy. 1995. Polyamines, floral induction and floral development of strawberry (Fragaria x anon ossa Duch). Plant Growth Reg. 17:157-165. Taylor, D. R., P. T. Atkey, M. F. Wickenden, and C. M. Crisp. 1997. A morphological study of flower initiation and development in strawberry (Fragaria x anonossa) using cryoscanning electron microscopy. Ann. Appl. Bioi. 130:141-152. Tehranifar, A,., and N. H. Battey. 1997. Comparison of the effects ofGA 3 and chilling on vegetative vigour and fruit set in strawberry. Acta Hort. 439:627-631. Thomas, B., and D. Vince-Prue. 1997. Photoperiodism in plants. Academic Press, San Diego. Thompson, P. A., and C. G. Guttridge. 1960. The role ofleaves as inhibitors of flower induction in strawberry. Ann. Bot. 24:482-490. Uematsu, Y., and N. Katsura. 1983. Changes in endogenous gibberellin level in strawberry plants induced by light breaks. J. Japan. Soc. Hort. Sci. 51:495-511. van Nocker, S. 2001. The molecular biology of flowering. Hort. Rev. 27:1-39. Vince-Prue, D., arid C. G. Guttridge. 1973. Floral initiation in strawberry: spectral evidence for the regulation of flowering by long-day inhibition. Planta 110:165-172. Voth, V., and R. S. Bringhurst. 1970. Influence of nursery harvest date, cold storage, and planting date on performance of winter California strawberries. J. Am. Soc. Hort. Sci. 95:496-500. Waithaka, K., and M. N. Dana. 1978. Effects of growth substances on strawberry growth. J. Am. Soc. Hort. Sci. 103:627-628. Weidman, R. W., and K J. Stang. 1983. Effects of gibberellins (GA 4 + 7 ), 6-benzyladenine (6BA) and promalin (GA 4 + 7 + 6-BA) plant growth regulators on plant growth, branch crown and flower development in 'Scott' and 'Raritan' strawberries. Adv. Straw. Prod. 2:15-17. Went, F. W. 1957. Environmental control of plant growth. Chron. Bot., Waltham, MA. Wisemann, N. J., and C. G. N. Turnbull. 1999. Endogenous gibberellin content does not correlate with photoperiod-induced growth changes in strawberry petioles. Austral. J. Plant Physiol. 26:359-366. Yamasaki, A., and M. Yamashita. 1993. Changes in endogenous cytokinins during flower induction of strawberry. Acta Hort. 345:93-99. Zhang, N., Yong, J., Hew, c., and X. Zhou. 1995. The production of cytokinin, abscisicacid and auxin by CAM orchid aerial roots. J. Plant Physiol. 147:371-377.
7
Flower and Fruit Thinning of Peach and Other Prunus Ross E. Byers Department of Horticulture Virginia Polytechnic Institute and State University Alson H. Smith, Jr., Agricultural Research and Extension Center 595 Laurel Grove Road Winchester, VA 22602 Guglielmo Costa Dipartimento di Colture Arboree University of Bologna Via Fanin 50 Bologna, 40126, Italy Giannina Vizzotto Dipartimento di Produzione Vegetale e Tecnologie Agrarie Udine University Via delle Scienze 208 Udine, 33100, Italy
1. INTRODUCTION
A. Fruit and Flower Thinning as Horticulture Practices B. Economic Benefits of Flower versus Fruit Thinning 1. Pollination, Fertilization, Ovule Abortion, and Compatibility 2. Competitive Assimilate Fruit Drop II. REPRODUCTIVE PHYSIOLOGY A. Flower Development B. Chilling C. Fruit Set
Horticultural Reviews, Volume 28, Edited by Jules Janick ISBN 0-471-21542-2 © 2003 John Wiley & Sons, Inc. 351
352
R. BYERS, G. COSTA, AND G. VIZZOTTO
III. ABSCISSION IV. THINNING PRACTICES A. Dormant pruning B. Flower Bud Inhibition or Abortion 1. Gibberellic Acid 2. Oils 3. Ethephon/GA Sprays at Leaf Fall and During Dormancy C. Flower Thinning 1. Mechanical Flower Removal 2. Chemical Flower Removal D. Fruit Thinning 1. Manual Fruit Thinning 2. Chemical Fruit Thinning E. Chemical Application Technology 1. Chemical Flower Thinning 2. Fruit Thinning F. Combinations of Flower and Fruit Thinning V. FUTURE PROSPECTS LITERATURE CITED
I. INTRODUCTION
A. Flower and Fruit Thinning as Horticultural Practices
Flower and fruit thinning of Prunus are commercially practiced in an effort to maximize crop value by optimizing fruit size, color, shape, and quality, to promote return bloom, and to maintain tree growth and structure (Farley 1923; Havis 1962; Byers and Lyons 1984 a,b; Webster and Andrews 1986; Byers 1989 a,b). In addition, thinning promotes more uniform annual bearing, which optimizes the use of labor and field, packaging and storage equipment. This chapter will emphasize flower and fruit thinning of peach and nectarine (P. persica), since the need to reduce whole tree photosynthetic demand of the fruit is much greater than for smaller stone fruit species where the ratio of total fruit weight per tree to total leaf area is low, such as with sweet cherry (P. avium) and tart cherry (P. cerasus). Certain European plum (P. domestica) and Japanese plum (P. salicina) cultivars set very heavy crops that can dramatically affect tree structure, even though the fruits are typically much smaller than peach fruits. The need for thinning other Prunus species, such as apricot (P. armeniaca) or sweet cherry, has been influenced by market prices for larger fruit, but tree structure is seldom an issue. In many regions, most sweet cherry cultivars require cross-pollination to set fruit and thus do not set as well as do peach cultivars, which are self-fruitful. As breeding programs introduce more self-fruitful cherry cultivars, the need for commercial fruit thinning will likely become more important.
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
353
Typically, the longer unwanted fruits remain on the tree, the greater the negative effect they will have on fruit and leaf size, tree growth, flower bud differentiation, flower bud hardiness, the next season's crop potential, and tree survival (Shoemaker 1933; Byers and Lyons 1985a,b; Byers et al. 1985, 1990; Myers 1986; Byers and Marini 1994). Estimating the maximum numbers of fruit to be retained to harvest requires an integrated knowledge of market price structure for different sized fruit, the genetic potential of a cultivar for fruit size and yield, and the effect of cultural practices (pruning, fertilization, irrigation, soils, scoring) on crop value. The optimum fruit size and yield for fresh versus processed markets may differ substantially by geographic region. For fresh peach fruit, the optimum diameter depends on customer preference and may range from 6.4 to 8.8 em. Typically, processors want fruit 6 to 8 em in diameter and uniform yellow flesh color for canning. The optimum date for thinning usually occurs before the demand for carbohydrates exceeds supply (Connors 1919; Costa et al. 1986; DeJong and Goudriaan 1989). Fruit growth kinetics based on daily demand for photosynthates, expressed as increase in dry weight per degree day (sink strength), may be useful in establishing an appropriate thinning date to achieve a specific fruit size. Environmental and cultural conditions (i.e., cultivar selection, light, water, soil, pruning, thinning, and fertilization practices) affect yield and fruit quality. The low tree densities (250 trees/hal typical in the eastern United States, allow a maximum fruit load of 500 to 700 peaches when nonirrigated, and perhaps 20 percent more when irrigated. These numbers could vary 10 to 30 percent or more, depending on environment and cultural practices. In irrigated areas of California or Australia with high light intensity, higher numbers are typical, particularly where largefruited cultivars can be grown or where smaller fruit are desirable for the processing market. In high density orchards when up to 1500 plus trees/ha are planted, trees must be irrigated to guarantee marketable fruit size. The major cullage factors for stone fruit are small fruit size and, secondly, insufficient color. Inadequate fruit thinning soon after bloom is considered responsible for small fruit size (Havis 1962). Typically, alternate bearing is not a problem with most stone fruits (exceptions are sweet cherry and some European plums), unless trees are cropped excessively or growth is extremely vigorous (Dorsey 1935). Fruit size, color, shape, flower bud differentiation, natural fruit set, and thinning response differ among cultivars. Recognition of these individual characteristics is extremely important for maximizing crop value. Certain peach cultivars produce large fruits (e.g., 'J. H. Hale' and 'Glohaven') while others produce smaller ones (less than 6.35 em in diameter) despite moderate croploads (e.g., 'Georgia Bell'). Furthermore, return bloom may be heavy on some cultivars (e.g., 'Biscoe,' 'Madison')
R. BYERS, G. COSTA, AND G. VIZZOTTO
354
but poor on others (e.g., 'Redglobe,' 'Blake') despite a moderate crop. Therefore, thinning practices must be selected for each individual cultivar within each geographic region and market. B. Economic Benefits of Flower versus Fruit Thinning
Bloom thinning peach trees can result in a 7 to 30% increase in fruit size and yield when compared to hand-thinning fruit 40 to 50 days after full bloom (AFB) (Fig. 7.1). The effect of thinning on the following year's 250..,..---------------,
A
...J
~ 200 +-----------w.~:t--_f:
(/)
~
III
a:
~ 150 l-
S
ff:
a:
100
"',',''',---f-----,;,,'''',,---~,
50
+-!i'%ll---~~;,'"J--j
w
III
~ Z
10
4
12
I" :I~tJ.;}-:- J,B'; l';~}- -f.lI}W
I-I-I~I~ ~':"O.;: .: -=:~,.;i :'.~"F,
-j
I :,.;l': .~::-='.l' ~ ~I=I=I!}--j~mj--{.l~ 4
;a.
4.5
3.5
:i:,::.:...:...:.;:'..: ':
..:.:L:,.w
.•
: :'.: :::.: .. ::.;, .. ::,:' :::;..: ...•... ::(.,
:.:, . . . ..:"'::" .•... .. '::.:.:.::" "•:": ..• : '.::":
10
12
80.,-----------------,
c
70 + - - - - - - - - - - - - - - - - j
o
2
4
6
8
10
12
THINNING TIME (WEEKSAFB)
Fig. 7.1. The influence of time of hand removal of flowers and fruits from 'Redhaven' peach trees on number of fruit per bushel (A), yield (B), and time of fruit maturation (C) (from Havis 1962).
355
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS Table 7.1. Calculated costs and returns in relation to fruit size of peach with 296 trees/ha and 700 fruit/tree (Byers 1989). Fruit diameter (cm)
No. fruit/ 35.24L (bushel)
Price !I 17.24 kg/ carton ($)
Crop return/ha ($)
Packing and transportation costs ($/ha)
Net profit/ha ($)
1.45-5.07 5.08-5.70 5.71-6.34 6.35-6.98 6.99-7.61 7.62-8.26
338 253 185 143 112 85
3 6 9 12 15 18
681 1812 3672 6348 10095 15390
1795 2057 2428 2851 3355 3992
-1114 - 245 + 1244 + 3497 + 6740 + 11398
flSoutheastern Peach Report, Vol. VI, No. 40, August 4,1987, Columbia, Sc.
crop has not been closely studied, but some increase in yield and size has been reported (Byers 1989a,b). However, the major economic effect of thinning is related to influences on the current season's leaf surface and crop load as the fruits compete for photosynthates. Trees with genotypes that mature earlier in the season, produce and set a higher percentage of flowers per tree, or produce smaller fruit usually derive a greater economic benefit from bloom thinning (or early fruit thinning) than late maturing genotypes. The cost of bloom thinning coupled with hand fruit thinning may result in annual costs similar to hand-thinning alone 40 to 50 days AFB (Byers 1989a,b). Alternatively, partial bloom thinning may increase crop value one to three times and profits several times because of increased fruit size, yield, and price (Table 7.1). Since prices usually increase with fruit size, adequate bloom thinning, followed by handthinning, irrigation, and other cultural practices may greatly increase profitability. II. REPRODUCTIVE PHYSIOLOGY
A. Flower Development
An understanding of reproductive phenology of Prunus is required to understand the ramifications of adjusting the crop load for maximum economic value. Typically, Prunus sp. differentiate very high numbers of flower buds but cultivars within species may differ widely (Table 7.2). Flower bud induction and differentiation begins soon after bloom and continues over a considerable length of time during the summer, as long as the shoots are actively growing. In peach, Dorsey (1935) determined that axillary flower buds were differentiated at eight nodes in the
356 Table 7.2.
R. BYERS, G. COSTA, AND G. VIZZOTTO
Fruit set of various stone fruit species. Fruit set References
Species
(%)
Almond
14-57
Apricot
0-60
Egea et al. 1991; Lichou et al. 1995; McLaren et al. 1995; Mahanoglu et al. 1995a,b
Cherry Sweet
0-40
Bargioni 1978; Webster et al. 1979; Roversi and Ughini 1985; Godini et al. 1997
0-27 2-50
Montalti and Selli 1984 Montalti and Selli 1984
Tart Self-pollination Cross-pollination Peach Clingstone Freestone
36-85 40-95
Kester and Griggs 1959; Socias i Company and Felipe 1987; Vasilakakis and Porlingis 1984; Kester 1994; Godini 1997
Filiti et al. 1982; Visai et al. 1985; Weinbaum and Erez 1983 Filiti et al. 1982; Visai et al. 1985; Weinbaum and Erez 1983
Nectarine
28-85
Filiti et al. 1982; Visai et al. 1985; Weinbaum and Erez 1983
Plum Open pollination Cross-pollination
16-55
Keulemans 1991 Keulemans 1991
tip and as growth continued, more buds were differentiated. However, under favorable conditions, peach and nectarine trees may set so much fruit that flower bud initiation may be inhibited at all nodes as the tip is growing. As the shoot grows, each node goes through a period when flower bud initiation is possible, but if cropload is too heavy or if growth is extremely vigorous, differentiation may not occur. Thinning (or harvesting) a substantial part of the crop reduces the competition between flower buds and developing fruits, shoots (Fig. 7.2A and 7.2B), and roots. Flower bud differentiation may be initiated again, if growth of the tip produces new nodes, but fruit removal will not cause initiation of new flower buds at nodes previously differentiated. In early maturing cultivars, sufficient growth may occur after harvest to allow sufficient numbers of buds to be formed during the remainder of the season. Flower initiation at the basal nodes is evident microscopically by about 50 days after bloom, and at subsequent nodes into late summer. The number of flower buds at each node and the total number of nodes with flower buds can be significantly modified by internal and external factors. Inter-
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
BLOOM THINNED
I
REDHAVEN
HAND THINNED
HAND THINNED
357
BLOOM THINNED
I CRESTHAVEN
I
Fig. 7.2. Bloom thinning increased leaf size, fruit size, and shoot growth of Redhaven peach trees (A), and increased flower bud numbers of Cresthaven trees (B) especially at the first 5 nodes. Since the basal flowers are the last to open, they may be less subject to injury from late bloom freezes (Byers et al. 1990).
nal factors include low nutritional status (C/N ratio) or high gibberellin (GA) content that inhibits flower bud formation (Zeevaart 1983; Goldsmith and Monselise 1970) while external factors include the time of thinning (Byers et al. 1990), climatic conditions (temperature, light, water), inorganic nutrition, and the application of plant growth regulators. Leaf nitrogen and dry matter content of shoots in one year are positively correlated with flower production per unit shoot length during the subsequent year (Marini and Sowers 1990). In both peach (Johnson et al. 1992) and cherry (Kenworthy 1974) any stimulation of growth caused by water, nitrogen, pruning, or other cultural management techniques may increase the ratio of vegetative to flowering buds. In contrast, low vigor (e.g., drought, poor soil aeration, root or trunk injuries, viruses, etc.) may favor flower bud initiation. Flore (1994) pointed out the inverse relationship between vigor and flower bud initiation in fruit crops; however, a heavy crop will inhibit both tree growth and flower bud formation.
B. Chilling In perennial woody plants, chilling is required for normal shoot growth and flowering in the spring (Weinberger 1950; Brown 1958; Monet and Bastard 1968; Legave 1975, 1978; Lam-Yam and Parisot 1990). If the
358
R. BYERS, G. COSTA, AND G. VIZZOTTO
chilling requirement has not been adequately met, the flower bud may die and abscise or flowerslfruits may abscise; thus the next season's growth, flowering, and yield may be compromised. When stone fruit trees are grown commercially under subtropical and tropical conditions' the winter chilling requirement may be partially overcome by chemical and cultural practices. The practices used to break physiological dormancy (Erez and Lavi 1984; Edwards 1987, 1990; Erez 1995) may greatly influence the final result of early flower and fruit thinning. The preceding season's chilling temperatures and duration playa key role in shoot vigor and speed of bud-break (Fuchigami and Nee 1987). The chilling period necessary to satisfy the rest requirement may vary greatly between species and cultivars (approximate temperatures between O°C and 7°C with a duration from 200 to 1000 hr); but its influence on final fruit set is unpredictable. Several methods (e.g., Utah Chill model, Asymcur) in different growing areas have been proposed to determine the time and temperatures that satisfy the chilling requirement (Bennett 1950; Doorenbos 1953; Samish 1954; Gurdian and Biggs 1964; Nienstaedt 1966; Richardson et al. 1974; Nooden and Weber 1978; Erez et al. 1979; Samish and Lavee 1982; Erez 1995). Even though much progress has been made in the selective breeding of new low-chilling peach cultivars, artificial techniques to break rest are still needed. Preconditioning floral buds in the autumn by cultural techniques reduces the need for chilling. Typically in warm winter growing regions, chemical sprays, mineral oils, cyanamide (Erez 1987; De Benito 1990), oil-cyanamide, and other chemicals (thiourea, potassium nitrate, gibberellic acid, cytokinins, paclibutrazole, and Armobreak (a surfactant made of a unique group of fatty amines) have been used to break dormancy, thus compensating for insufficient chilling (Saure 1985). C. Fruit Set
The number of fruit set per tree depends on the number of flowers per unit length of wood, the amount of fruiting wood, climatic conditions during pollination/ fertilization (Byers and Marini 1994), adequate chilling, pruning, and many other environmental and cultural factors. In peach, fruit set between seasons has been as few as 10 percent of the flowers or as great as 85 percent (r. e. Byers unpublished). Obviously, the amount of natural fruit set may greatly influence the numbers of fruit that need to be removed to optimize crop value. Fruit set is extremely variable among Prunus species and cultivars. In addition, reported values differ considerably for different environmental conditions (Table 7.2). The number of reproductive sinks early in the season can be extremely high in stone fruit, up to 50,000 flowers per tree in sweet cherry, and 20,000 in peach. These flow-
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
359
ers and fruit represent a tremendous demand on the tree reserves before adequate leaf surface develops to support shoot and fruit growth (Keller and Loescher 1989). Furthermore, the number of peach fruits on an unthinned and unpruned tree is often too high for the tree to support, resulting in small fruit and limb breakage (Southwick et al. 1996a,b). In some peach cultivars, fruit set may be so great that shoot growth, and leaf number, and fruit enlargement are so inhibited that trees may appear to have very few leaves even as late as 50 days after full bloom (AFB). 1. Pollination, Fertilization, Ovule Abortion, and Compatibility. Pollination, followed by fertilization of the ovule, is required for fruit set in most stone fruit cultivars. Unfertilized fruit typically abscise, but some cultivars retain a small percentage until harvest. In some peach cultivars, these fruit mature later than the main crop and are referred to as "buttons." If temperatures are below 12° to 15°C during bloom and/or the 7 to 10 days following bloom, poor pollination and pollen tube growth will occur, resulting in a low percentage of fertilized ovules, and a large number of fruit abscising within 50 days AFB. Fruit from unfertilized flowers will start slowing in growth rate about 15 to 25 days AFB and will typically abscise before the pit lignifies (pit hardening stage) (r. e. Byers, unpublished). The fruit and seed developing from nonfertilized flowers may not be distinguishable from those from fertilized flowers for the first 25 days AFB. Workers hand-thinning peach, nectarine, plum, and apricot trees within 40 days AFB, and particularly within 15 to 25 days AFB, may find it difficult to visually differentiate between fruit that will drop naturally and those that will remain on the tree, as ovules of unfertilized fruit mayor may not have turned brown. Application of chemical sprays that inhibit pollination and fertilization increase the number of "buttons"; therefore, assessment of the degree of thinning by these chemicals may be difficult, and might complicate follow-up handthinning in the first 25 days AFB. Since weather conditions during the pollination and fertilization period may cause 50 to 80 percent of the fruit to remain unfertilized, workers that are hand-thinning at bloom may over-thin. To avoid this, partial bloom thinning (i.e., leaving two to four times as many flowers as needed), followed by fruit thinning 35 days AFB is typically practiced. This maximizes the fruit size and yield benefits of early crop reduction without danger of over-thinning. Peach and nectarine cultivars are typically self-compatible and frequently are not as subject to alternate bearing as other stone fruit species if good cultural practices are used. When weather is poor for cross-pollination, self-incompatible cultivars (e.g., 'J.H-Hale' peach, 'Ruby Red' nectarine) set poorly, resulting in considerable financial loss.
360
R. BYERS, G. COSTA, AND G. VIZZOTTO
Apricot, European plum, Japanese plum, and sweet cherry require fruit thinning only when fruit set is very high and/or the price for larger fruit greatly increases crop value. Thinning of the fruitlets for these species may be practiced, to increase fruit size, to avoid branch breakage or stimulate flower initiation (Webster and Andrews 1986). Unfortunately, predicting final fruit set at bloom is frequently difficult. Thompson and Liu (1973) proposed that erratic fruit setting of 'Italian' prune induced by cool weather was the result of ovule abortion. Breeding of cultivars with enhanced ovule longevity and consistent annual production may increase the need for thinning (Hanson and Breen 1985; Sun et al. 1991). Apricot cultivars are generally considered self-compatible (Bailey and Hough 1975; Limongelli and Cappellini 1978; Cappellini and Limongelli 1981), but some cultivars have incompatibility problems in some areas (Lamb and Stiles 1983; Nyujt6 et al. 1986); thus single-cultivar apricot orchards should beavoided in these regions (Burgos et al. 1993). 'Canino' apricot produces self-compatible pollen, but the pollen germinates very poorly (Mahanoglu et al. 1995a,b). In the self-fertile 'Rouge de Roussillon,' pollination and fertilization do not limit fruit set; but poor fruit set may occur because of embryo sac abnormalities during seed formation (Lichou et al. 1995), or fruit competition during cloudy weather. In plum, some cultivars yield inconsistently because of poor pollination, low pollen viability, slow pollen tube growth, poor nutritional status of the tree, and/or short embryo sac longevity as a consequence of unfavorable environmental conditions, especially cloudy weather. Cross-pollination with suitable cultivars is therefore recommended (Keulemans 1991). In sweet cherry (Looney 1988), sour cherry, and almond (P. amygdaJus), the number of fruit/shoot is very high, but fruit thinning is not commercially practiced because fruit weight/cm 2 trunk cross-sectional area is still low relative to that in peach or apple. However, areas where set is high, crop value can be increased substantially by early flower or fruit thinning to increase fruit size. Hand-thinning is considered too costly for these fruits because fruit numbers per tree is very high and trees are often very large. In these crops, chemical thinning technology is needed, particularly as high fruit-setting cultivars are introduced. A study of the most important cultivars in Italy indicated that only 'Montmorency,' 'Schattenmorelle,' 'Nabella,' and 'Northstar' were selfcompatible (Montalti and Selli 1984). Standard sweet cherry and almond cultivars are self-incompatible. Because of incompatibility, the most important commercial sweet cherry cultivars require specific pollinizers (Bargioni 1978; Lugli and Sansavini 1997). Almond cultivars are typically self-incompatible. To achieve a commercial fruit set (30% or higher) pollinizers are required (Kester and Griggs 1959). In both almond
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
361
and sweet cherry, full or partial self-compatibility, late bloom, and high fruit set are the main objectives of breeding programs (Kester 1994; Godini et al. 1997). The rapid increase of the almond industry in California may have resulted from the introduction of self-compatible cultivars. As such programs become more successful, the need for thinning all stone fruits will likely increase. Very early flowering (almond < apricot < plum < sweet cherry < tart cherry < peach = nectarine) and consequent susceptibility to freeze damage is also a major influencing fruit set factor. Similarly, winter hardiness and winter freeze injury of species and cultivars may differ. In one study, cultivars of freestone peach were more winter hardy (70% of the cultivars examined during a spring freeze damage were resistant) in comparison with cultivars of nectarine and genetic clingstone peach (15 to 16% resistant) (Filiti et al. 1982). 2. Competitive Assimilate Fruit Drop. Abscission and inhibition of growth of young fruit may result from strong competitive influences from other fruit, shoots, roots, xylem, phloem, and other cellular growth within the tree (Costa et al. 1983; Byers et al. 1984b; Byers et al. 1985; DelValle et al. 1985). A shortage of metabolites during certain early stages of fruitlet development may reduce their sink strength and further reduce fruit growth at later stages when metabolite supply may not be limiting. Competing sinks may use most of the available metabolites and ultimately reduce tree growth, fruit growth, flower bud differentiation, and/or cause abscission of weaker fruit. Under optimal environmental conditions and cultural management, metabolite supply is mainly determined by intersink competition, which may be reduced by the removal of a portion of the developing fruitlets (thinning). If there is substantial competition for the current season's photosynthates, the smaller and weaker fertilized fruit may abscise from the tree at about 45 days AFB. This drop is usually referred to as "June drop" even though it may not occur at that time of year. A significant "June drop" indicates that the fruit were competing significantly with each other and that the remaining fruit will be smaller at harvest than if no such drop had occurred. Fruit lost to "June drop" or hand-thinning represents a loss of photosynthetic reserves, which cannot be regained. Fruit drop caused by poor pollination and fertilization may occur 30 to 45 days AFB and can be confused with drop caused by competition between fruit. Since light is required for photosynthesis, three to four days of cloudy weather between 35 to 50 days AFB may reduce the supply of photosynthate causing fruit abscission in stone fruits (Byers and Lyons, Jr. 1984; DelValle et al. 1985). Since prolonged cloudy periods do not usu-
362
R. BYERS, G. COSTA, AND G. VIZZOTTO
« w a: «
..J
~
Q
I-
0
w
CJ) CJ) CJ)
0 a: 0
In
:IE
11 10
7 6
5
E
3
a:
2
u.
UNTHINNED CONTROL
ab
8
4
~:::>
ab
a
•
9
::i
N
a
--'-SHADED 10 DAYS
12
de
•
HAND THINNED CONTROL
0 15
20
25
30
35
40
50
74
DAYS AFTER FULL BLOOM
Fig. 7.3. The influence of shading entire 'Cresthaven' peach trees at various times after full bloom on fruit abscission (Byers et al. 1985). Mean separation by Duncan's multiple range test, 5 percent level.
ally occur at this time in the season, fruit drop would not occur until a week or so later. Thinning induced by shading (Fig. 7.3) will increase the average size of the remaining fruit at harvest because of the crop reduction and selective abscission of smaller fruit. If a significant reduction in flowers or fruit number has occurred in the first 20 days AFB, "June drop" would not be expected, since fruit competition would not be sufficient to cause abscission. III. ABSCISSION
Abscission involves a series of programmed events that culminate in altered cell morphologies and weakening of tissue, which may be in response to tissue damage or a part of normal physiological development (Bleecker and Patterson 1997). Anatomically, abscission is the consequence of the dissolution of the middle lamella between adjacent cells in a specialized zone consisting of one or more layers of small, isodiametric cells, which are densely cytoplasmic. The fracture usually occurs in the plane of the middle lamella (Addicott 1982; Sexton and Roberts
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
363
1982). In peach, the fruit abscission layer develops across the vascular bundles leading in part to the separation of vascular strand (Tirlapur et al. 1995), and the final separation may take place by mechanical fracturing, as in tart cherry (Stosser et al. 1969). Typically, the major enzymes involved in cell wall dissolution are exo- and endo-polygalacturonase (PG), and endo-J3-1,4-glucanase (EG) (Ramina et al. 1993; Sexton 1995). Although the final result is the same for leaf and fruit abscission, the induction mechanisms differ for the two organs. In peach fruit pedicels, cell wall digestion starts from the middle lamella, and subsequently extends to the entire parietal mass. In leaf pedicels, cell enlargement occurs after activation of the abscission zone (AZ), involving the separation layer of the fruit, and cells of the adjacent tissues at the adaxial side in a proximal position (Rascio et al. 1985; Ramina et al. 1993). Bonghi et al. (1992) found that EGase activity was high in peach leaf abscission zones but much lower in fruit abscission zones, whereas PG activity was not detected in abscission zones of leaves, but was present at very high levels in those of fruit. These differences in hydrolytic activities (enzymes) are of potential practical use because they may permit chemical stimulation of fruit abscission without leaf abscission (Hadfield and Bennett 1998). Abscission is restricted to specific locations in peach and nectarine fruits (Fig. 7.4). Three abscission zones (AZ1, AZ2, and AZ3) exist between the fruit and the stem (Nelson et al. 1984; Rascio et al. 1985), and are recognizable before the onset of cell wall dissolution and are consistent with the target-cell hypothesis proposed by Osborne (1979). Flowers and small fruits (early June drop) separate from the tree at the basal abscission zone (AZ1) between pedicel and peduncle, while AZ2 (located between the flower receptacle) and the peduncle at AZ3 (between the fruit and the receptacle). These zones are activated in mid(AZ2) and late (AZ3) June drop (Rascio et al. 1985). The AZ3 resembles that in sweet cherry (Wittenbach and Bukovac 1972) and plum (Simons and Chu 1975). The hormonal regulation of the early fruit abscission process differs from senescing pedicels of ripening fruit, even though both may be influenced by ethylene (Sexton and Roberts 1982; Abeles et al. 1992). Ethylene biosynthesis increases before abscission of many organs, but abscission can occur without a rise in ethylene biosynthesis. Inhibitors of ethylene biosynthesis or action may interfere with both ethyleneinduced abscission and also abscission caused by other stresses (Reid 1985). The AZ3 zone does not selectively produce ethylene upon abscission induction, but ethylene biosynthesis may occur in nonzone tissue. The
364
R. BYERS, G. COSTA, AND G. VIZZOTTO
Fig. 7.4. In peach, abscission may occur at the base of the peduncle [abscission zone (AZ1)] if the bud, pistil, or fruit has been injured before bloom or up to approximately 30 days AFB. Abscission at AZ2 may occur because of injury, exposure to ethylene, or fruit competition mid-season, or at AZ3 late in the "competitive fruit abscission" ("June drop") stage or at harvest.
specific abscission response of AZ3 may be due to changes in ability of ethylene to activate specific genes and to stimulate the secretion of cellwall degrading enzymes, such as EG in the separation zone (Sexton et al. 1985; Ruperti et al. 1998). Abscission zone response to ethylene is required in the fruit pedicel in a manner that may be analogous to ripening fruit. The presence of ethylene alone is not sufficient to induce abscission (Lanahan et al. 1994), but ethylene may induce cell wall hydrolysis responsible for the degradation of the middle lamella and the loosening of the primary cell wall of the separation layer cells. Ethylene regulates at the transcriptional and/or translational level the activity of the main enzymes involved in the process (Ruperti et al. 1998). Abscissic acid (ABA) and ethylene can influence auxin synthesis and transport and may markedly counteract the suppression of abscission by auxin (Sexton et al. 1985). The progress of abscission is determined by the accelerating effects of ethylene on the influence of auxin concentration. Ethylene, through its effect on chlorophyll degradation (Choe and Wang 1986) and ABA, by increasing photorespiration (Popova et al. 1987), may reduce the production and availability ofleaf assimilates. In addition, the availability of minerals and nutrients translocated in the
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
365
respiration stream may be reduced due to the restricted transpiration rate. These imbalances and localized deficiencies in dry matter may be critical factors in hastening abscission of leaves and fruits (Noga and Bukovac 1990). Ethylene application also inhibits growth in peach (Ramina et al. 1986) and may be the result of processes previously induced by ethylene (Bleecker and Patterson 1997). IV. THINNING PRACTICES
A. Dormant Pruning
Dormant pruning is frequently used to reduce the current season's flower bud complement; and if substantial pruning is not done before growth begins, photosynthetic reserves stored in the roots, trunk, and limbs may be wasted on the development of flowers, shoots, and fruit (Fig. 7.5).
Fig. 7.5. In the year following a freeze that defruited trees, tree growth (A) flower numbers (B), tree density (C), and fruit number (D) was several times greater than in trees carrying a typical crop. If trees are allowed to flower without substantial dormant pruning, the greater competition between fruits may cause a greater than normal fruit drop about 45 days AFB. Unpruned trees will also reduce spray penetration of chemical bloom thinners so that chemical deposits from adjoining row sprays will lower the thinning response.
366
R. BYERS, G. COSTA, AND G. VIZZOTTO
Shoemaker (1933) and Marini (2000) suggested that substantial pruning might be used as an early season thinning technique. A grower may choose to prune twice; the first time to remove major bull canes over 1 m in length and the second to provide tree containment. A second pruning may be used after the potential of winter killing of flower buds has passed as a flower bud thinning technique. However, Marini's (2000) work dearly shows that a freeze after winter pruning in 1997 improved crop value. The freeze in 1997 partially thinned the trees and thus allowed greater yields of more marketable fruit on trees pruned less severely (Table 7.3). In 1998, no freeze occurred, thus pruning to limit the number of bearing shoots to only 73 shoots per tree resulted in higher yields of larger fruit and increased crop value (Table 7.3). Even though dormant pruning can be used as an early thinning technique, the necessity for further thinning after pruning may be substantial in some regions. When bloom thinning, a crop loss, or a partial crop loss occurs, detailed pruning for partial thinning may be even more imperative because the number of flower buds/tree may be four times, and bearing shoots/tree twice, that of trees thinned 45 days AFB (Byers 1990). In addition, pruning or chemical flower bud inhibition allows additional time to further reduce the potential crop prior to bloom and before bloom or post thinning practices are initiated.
Table 7.3. The effects of retaining various numbers of shoots per tree on fruit set, yield, fruit weight, and crop value of 'Norman' peach trees (Marini 2000). No. fruit per tree
Shoots/tree
Before thinning
Removed in thinning
Harvested
Yield (kg/tree)
FW/fruit (g)
Crop value ($/tree)
73 110 146 220
296 352 432 510
27 58 81 168
1997 (Freeze) 269 294 351 342
91.6 97.1 111.6 108.0
156 151 146 147
34.90 32.87 37.67 37.54
73 110 146 220
720 910 920 1600
227 415 518 1180
1998 (No freeze) 560 480 420 430
59.0 55.8 42.6 44.5
123 118 113 111
33.00 28.00 21.00 22.00
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
367
B. Flower Bud Inhibition or Abortion 1. Gibberellic Acid. Gibberellic acid (GA 3 ) inhibits flower bud formation in a wide variety of woody fruit trees including cherry, peach, nectarine, apricot, and almond (Zeevaart 1983). Goldsmith and Monselise (1970) determined that GA 3 application increased cellular division and expansion in the sub-apical zone, which subsequently increased internode length in citrus and reduced the number of flower buds at each node. The increased proportion of vegetative buds to flower buds resulted in a greater leaf to fruit ratio in the following year. Byers (1990) also found increased shoot length, shoot number, and bud numbers per centimeter of shoot length. In stone fruit, both GA 3 application time (Fig. 7.6) and rate per ha influence the number of flowers initiated (Hull and Lewis 1959; Bradley and Crane 1960; Stembridge and LaRue 1969; Byers et al. 1990). GA 3 sprays applied at full bloom through mid-season typically inhibit flowering in peach, but applications later in the season induce abortion of previously differentiated buds (Stembridge and LaRue 1969). GA 3 application prior to leaf fall caused some delay of bud development (Fig. 7.7B), flowering, and increased bud hardiness the following spring (Proebsting and Mills 1964; Stembridge and La Rue 1969). A wide window of opportunity exists for either rate or timing of GA 3 sprays for reducing flower bud numbers by varying degrees (Edgerton 1966; Brown et al. 1968; Stembridge and La Rue 1969; Corgan and Widmoyer 1971; Intrieri and Sansavini 1972; Byers et al. 1990; Southwick and Yeager 1991; Oliveira and Browning 1993; Southwick et al. 1995b; Lemus 1996; Costa and Vizzotto 2000). In California, application of GA 3 in mid-June was less effective than when applied from mid-June to early July (Southwick et al. 1996b). The time of GA 3 spray application can have a major effect on bud development along specific shoot sections. GA 3 applied when the largest shoots are about 10 to 15 cm in length (30 to 70 days AFB) will inhibit flower bud development at the base and mid-sections of the shoots, with maximum effect at about 50 days AFB (Byers 1990). Since greater numbers of flower buds are produced at the basal nodes of shoots, and on short, weak shoots that have many buds and shorter internodes, GA 3 can specifically reduce these buds by timing the spray at the time they are being differentiated (Byers et al. 1990). GA 3 , under the name of Release LC (Valent Biosciences), is currently registered only in California. This material could be particularly useful in inhibiting flower-bud formation after a crop loss, or on certain cultivars that have an extraordinarily large number of buds such as 'Bisco'
R. BYERS, G. COSTA, AND G. VIZZOTTO
368
30 , . . - - - - - - - - - - - - - - - - - - - - - - - - - . - 200
---~
25
I0 0 ::I:
R.OWER BUDS PER SHOOT
180
FRUIT PER SHOOT FRUIT VOLUME
160 140
20
120
(J)
~
:5 IX: LL
IX:
15
100
0
IX:
80
W
;: ..J
LL
:E ~ w :E ~
..J
0
>
(J)
0
-
C?
I-
:5 IX: LL
10 60 40
5
20
O-L------------
o
12
--J..
36
0
47
GA3 SPRAY DATE (DAYS AFB)
Influence of time of GA;) application on numbers of flowers and fruit per shoot, and on individual fruit volume in the subsequent year (Byers et al. 1990).
Fig. 7.6.
or 'Redhaven.' Additionally, GA 3 could be used in conjunction with a regular bloom thinning program where winter injury to flower buds is not a significant problem. GA 3 might also be used to reduce flower bud numbers at the base of shoots so that rope thinning would be more uniform and effective (Byers et al. 1990) (Fig. 7.8ABC). Since the effect of GA 3 is time- and concentration-dependent, a wide window exists for reducing flower bud numbers by 50 to 75 percent. In addition, the influence of environment and adjuvants on absorption and activity of GA 3 has
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
369
Fig. 7.7. Influence of soybean oil (8 %) applied in the dormant season on killing of a peach pistil (A) (note flower bud began enlarging with dead pistil). Previous season GA;{ spray delayed development of peach pistil in the subsequent season (B) resulting in lower percentage of flowers setting fruit. Injury to the peach pedicel (C) following application of ammonium thiosulfate. Dead flowers 30 days after bloom still attached to the shoot (D) caused by ammonium thiosulfate phytotoxicity to the pediceL At 25 days AFB unfertilized fruits (E) are difficult to distinguish from larger fertilized fruit (note development of button nonfertilized fruits that will abscise about 50 days AFB).
370
R. BYERS, G. COSTA, AND G. VIZZOTTO
not been adequately studied. An additional benefit of preharvest GA 3 applications is maintenance of flesh firmness and a slight delay in ripening (Southwick and Yeager 1995). On apricot, the effect of GA 3 is concentration-, time- and formulationdependent (Southwick and Yeager 1995; Southwick et al. 1995a). Over a three year period, the highest GA concentration used strongly reduced flower numbers the subsequent season. GA 3 greatly reduced handthinning time and increased fruit size and firmness; however, the percentage of flowers setting fruit was not affected (Southwick et al. 1997). On prune, GA 3 improved fruit set (Webster and Goldwin 1981) and quality (Boyhan et al. 1992) in the year of application and inhibited flowers (Webster and Goldwin 1981). In several climatic regions, flower bud inhibition may not become widely accepted because of the potential risk of subsequent damage to buds by winter or spring freezes. This may further reduce cropping to sub-optimal levels (Byers et al. 1990). 2. Oils. Vegetable and petroleum oils applied as a dormant spray at 75 to 110 L/ha (single or multiple applications) are known to reduce tree and flower bud respiration, delay bud break, and kill 40 to 60 percent of the flower buds (Fig. 7.7A) (Call and Seeley 1989; Deyton et al. 1992; Myers et al. 1996). However, considerable research is still needed to determine the proper time, rate, and number of applications needed. Where winter temperatures drop below -15°C, the risks of dormant oil may be detrimental to tree and flower bud survival, fruit size, and tree growth.
3. Ethephon/GA3 Sprays at Leaf Fall and During Dormancy. Autumn sprays of GA 3 and ethephon on peach, apricot, and sweet and tart cherry can delay blossoming and increase floral bud hardiness (Proebsting and Mills 1973; Browne et al. 1978; Soni and Yousif 1978; Walser et al. 1981; Buban and Turi 1985). Crisosto et al. (1989) reported that application of ethephon during several different leaf-fall stages delayed 'Redhaven' peach bloom the following year. However, ethephon application at the 10 percent leaf drop stage reduced flower and fruit number by almost 50 percent, whereas later applications had little effect. Bud hardiness, measured as the percentage of bud survival, was greatest following ethephon treatment at 50 percent leaf drop. Fruit set was not affected by any of the ethephon treatments. In other experiments, GA 3 and ethephon sprays applied in October or November killed peach flower buds (Williams 1989). This effect was
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
371
Fig. 7.8. Stationary (A) or rotating (B) rope drags are an effective and rapid method for peach flower bud removal. As a result of bloom thinning, basal buds (C) are difficult for rope drags to thin due to adjacent twigs that hold ropes away from buds. High pressure water streams (D) can be directed to narrow crotch areas that can not be thinned by rope drags (Byers, unpublished).
related both to date of application and concentration of the chemicals, as previously shown by Stembridge and La Rue (1969). Gianfagna et al. (1986) found that 100 and 200 mg/L of ethephon applied in autumn delayed flowering of peach several days, but killed some flowers. Postharvest sprays of GA3 applied to 'Patterson' apricot reduced flower number (Southwick and Yeager 1991) and, in some experiments, reduced fruit set. Similar effects were obtained with ethephon on 'Shirokaga' and 'Inazumi' Japanese apricot (Frunus mume) (Paksasorn et al. 1995). High-volume sprays of ethephon to 'Victoria' plum, just prior to leaffall, delayed blossoming by several days the following spring. However, blossom quality and fruit set were frequently poorer on the ethephonsprayed trees than on the controls; the addition of GA 3 overcame the effects on flower quality and increased yields (Webster 1984a, 1984b; Webster and Andrews 1986).
372
c.
R. BYERS, G. COSTA, AND G. VIZZOTTO
Flower Thinning
Flower or early fruit removal will conserve photosynthetic reserves (stored from the previous season or produced in the current season) by reducing competition between all organs throughout the tree. For this reason, thinning may increase vegetative shoot growth, flower bud differentiation, flower bud hardiness, fruit size, and yield (Byers 1989a, 1989b; Byers et al. 1990; Byers and Marini 1994). When a peach tree is bloom-thinned (or the crop is lost due to a freeze), two to five times more flower buds/unit length of wood plus additional shoot length (Fig. 7.2) are produced compared with trees hand-thinned 40 to 50 days after bloom (Byers and Lyons 1984a; Byers and Marini 1994). Therefore, the need for early thinning may be even greater in the years following a partial or complete early season crop loss. After a freeze or when trees are bloom-thinned, the greatest increase in flower bud numbers occurs near the base of the current season's shoots and on short shoots throughout the tree canopy (Byers et al. 1990). Fruit that develop at these locations are typically the smallest fruit on the tree; and, if not removed at bloom, will result in a large number of small fruit. Elimination of the crop by a spring freeze would cause substantially more shoot growth and flower bud numbers than would bloom thinning. Since basal flower buds on the shoot are the last to open in the spring, they may provide some protection from late spring frosts (Byers and Lyons 1985a; Byers 1989a, 1989b; Byers et al. 1990). In any case, no more than 3000 to 6000 flower buds should remain on a normal-sized peach tree after bloom. If peach trees are not thinned or are thinned very late (60 days AFB) extreme competition between fruit (Fig. 7.2A and 7.2B) may have a major effect on vegetative growth and flower bud differentiation so that the subsequent season's crop may be compromised (Byers and Lyons 1985a; Myers 1986; Byers et al. 1990; Byers and Marini 1994). Overcropped treesmay cause reduced tree vigor, smaller crops of more undersized fruit, and trees more susceptible to disease, cold injury, and a shortened tree life (Shoemaker 1933). Heavy detailed pruning in the winter plus flower thinning in the spring can reduce flower bud numbers and prevent over-cropping, small fruit size, and poor shoot growth. Heavy nitrogen fertilization of trees cannot compensate for the loss in photosynthetic reserves from over-cropping. If not thinned adequately, many peach and nectarine cultivars may exhibit biennial bearing habit. However, because trees will respond to good cultural management practices, commercial orchards typically will produce an adequate number of flower buds each year and thus mask the alternate bearing cycling.
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
373
Annual pruning, thinning, fertilization, and cultural practices are critical to maximizing crop value (fruit size x yield x price), by assuring adequate vegetative growth, flower bud numbers, and carbon reserves for the next season. 1. Mechanical Flower Removal.
Hand or Brush Thinning. Hand or brush thinning (e.g., plastic or wire brushes, limb switches, gloves, etc.) of peach and nectarine has been practiced for over 75 years. Mechanical flower removal, unlike chemical thinning allows visual determination of the number and location of flowers throughout the canopy immediately after thinning. Rope Drags. Tractor-mounted, fixed or rotating rope curtain drags, have been used to remove a large number of flowers very cheaply from peach and nectarine trees (Baugher et al. 1988; Baugher et al. 1990, 1991). Rope strands 2.5 to 3.2 cm in diameter and 450 to 500 cm in length are hung over a horizontal bar at 5-cm intervals and dragged over a tree in full bloom (Fig. 7.8A & 7.6B). This removes the flowers most effectively in the tops and periphery of the tree. Dragging ropes in opposite directions two to four times increases uniformity and the degree of thinning with each pass. Rope spacing may be varied to change the amount of thinning during each pass. Rotating rope drags and spiked-drum, impact shakers (Glenn et al. 1994) are other variations of the rope curtain drag. Unfortunately, flower buds in narrow angle crotches in the top and sides of the tree are not adequately thinned by the ropes. Since flower thinning increases basal bud development at nodes one through five, flower thinning the previous season will cause additional clustering of flower buds in crotches at the junction of current season and two-yearold wood (Fig. 7.8C). In addition, rope drags are more effective on trees with flat tops which may not be the most productive fruiting system. Water Thinning. High pressure streams of water (Fig. 7.8D) from single or multiple spray gun nozzles mounted on a sprayer or tractor can effectively remove flowers from stone fruit species that have short, inflexible stems (Byers 1990). Irrigation nozzles (40 mm diameter) with plastic water straighteners provide a water stream with adequate force if pump pressure of 31.6 to 38.7 kg/cm 2 is maintained (Byers 1990). A single nozzle will require 4.5 to 5.7 L/minute; thus a substantial pump and 14,000 to 19,000 L of water are required for full-size trees that have been adequately pruned in the dormant season. This method may not be practical, since labor costs and the amount of water required may become prohibitive, particularly for dense, nonpruned trees.
R. BYERS, G. COSTA, AND G. VIZZOTTO
374
2. Chemical Flower Removal. The primary disadvantage of flower thinning is the potential for subsequent killing of flowers or fruit by spring frosts, and the uncertainty of favorable environmental conditions for pollination, fertilization, and fruit set (Batjer 1965). Since most chemical thinning agents rely on an interference with the natural process of pollination and fertilization, cutting the stigma and one half the style off demonstrated the importance of natural fruit set and the interfering treatment (Fig. 7.9). Even though many researchers indicated that bloom thinners might have limited commercial value, the economic impact of early thinning must be weighed against several factors. These include the probability of a local freeze, earliness of bloom, value of crop in relation to costs, later fruit hand-thinning costs, availability of labor, and the potential for biennial bearing for each cultivar.
Elgetol. Sodium 4,6-dintro-ortho-cresylate (DNOC), known under its commercial name Elgetol, became the first important apple flower thinning agent (Batjer and Thompson 1948; Williams 1979) and remained so for over 40 years until registration was canceled in 1990 by the Environmental Protection Agency. Elgetol thinning at bloom in the western United States had been considered a part of a total thinning program that was essential for maximizing fruit size and for providing an adequate return bloom for the next season (Williams 1993, 1995). Hildebrand (1944) showed that Elgetol inhibited fruit set when applied as late as 32 h after
'Sa-
100 90
LL
80
c
70
~ ~ Q)
60
0')
E
~~~g~;:~~ ~
-o-Control ..... Pink -.-Bloom ~ Petal Fall (63%) ~ Petal Fall (74%) ---t:r Petal Fall (92%) -+- Petal Fall (100%) ""'*- Shuck Split
50
~ 40
~c
~
et
95% Confidence Interval
Stigma Cut Off
30 20 10
o
-3
18
35
50
62
Days After Full Bloom Fig. 7.9.
Effect of time of stigma removal on fruit set of peach (R. E. Byers, unpublished).
375
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
pollination. Microscopic observation showed pollen tube growth was approximately halfway down the style 32 h after pollination (Hildebrand et al. 1944). When Elgetol was applied just before wet and humid periods, it caused fruit and foliage injury and erratic results; thus, it was used very little in the eastern United States where humid conditions prevail. In addition, re-wetting and poor weather conditions during pollination and fertilization resulted in variable fruit set and unpredictable responses related to the Elgetol application. Cancellation of Elgetol registration caused universities and chemical companies to seek a replacement for it (Williams 1994). Consequently, the potential for development ofimproved chemical thinning agents caused a resurgence of interest in flower thinning in the United States (Byers 1997). Prior to 1991, investigation of new flower thinning agents was a low priority in the eastern United States due to erratic thinning and injury to leaves caused by Elgetol. In the 1980s, fertilizers, surfactants, and desiccants were investigated for flower thinning of peach trees in the United States (Table 7.4). Several of these chemicals are effective bloom thinners for apple including endothall, ammonium thiosulfate (ATS), and long chained fatty acids (Byers and Lyons 1985; Williams 1993; Williams 1995; Southwick et al. 1995a,b; Bound and Jones 1997, Byers 1997; Fallahi 1997). Table 7.4. Effects of airblast spray applications of several flower thinning agents and surfactants on 'Redhaven' peach fruit set (Byers and Lyons, Jr. 1985).
Treatment Control Hand thinning ATS + no surfactant ATS + Spray-Aide® ATS + Spray-Aide® ATS + Spray-Aide® ATS + X-77® ATS + Spray-Aide® ATS + Dithane Z-78® CC-42 (polyoxypropylene ammonium chloride) DuPont WK® Endothall®+ X-77® Endothall®+ X-77® Methyl oleate+ Na C0 3 NH 4 N0 3 + X-77® SN-50 (oxyalkylated alcohol)
No. fruit/cm 2 limb cross sectional area
Fruit diam. (cm)
0 0 30 mIlL 30 mIlL + 1.25 mIlL 30 mIlL + 2.5 mIlL 30 mIlL + 5 mIlL 30 mIlL + 5 mIlL 30 mIlL + 5 mIlL + 9.6 giL 25 mIlL
16.2 aO 5.0 d 3.8 de 3.7 de 2.7 de 2.7 de 2.8 de 3.7 de
4.80 e 5.13 de 6.32 a 6.12 ab 6.45 a 6.50 a 6.60 a 6.20 a
11.7 bc
5.54 cd
25 mIlL 0.75 mIlL + 5 mIlL 0.75 mIlL + 2.5 mIlL 20 mIlL + 38.4 giL 120 giL + 5 mIlL 25 mIlL
1.0 e 9.7 cd 9.5 cd 14.8 ab 2.3 e 6.7 d
6.32 5.44 5.61 5.13 6.38 6.02
Formulation ratelL
a d bcd de a abc
°Means separation within columns by Duncan's new multiple range test, 5 percent level.
376
R. BYERS, G. COSTA, AND G. VIZZOTTO
Fertilizers. Of the fertilizers evaluated as flower thinners for peach, ammonium thiosulfate (ATS) (National Chelating Corp.) was among the most effective and easiest to use since it was formulated as a liquid (Byers and Lyons 1984a, 1985a,b). However, urea, ammonium nitrate, calcium nitrate, and many other phytotoxic liquid fertilizer formulations were found effective. The use of ATS fertilizer for flower thinning has been commercially practiced without registration in peach and apple orchards in the United States. Applications made in the later stages of apple bloom (90% open flowers) caused more russetting or "marking" of the apple, but most of these chemicals were more effective and less injurious to peach, nectarine, and other Prunus since stone fruit are protected by the corolla from direct spray contact at bloom (Byers 1997). Many caustic chemical sprays may interfere with ovule fertilization if applied soon after flower opening, but the mode of action also includes injury (Fig. 7.7C) to the pedicel (Erez 1975; Byers and Lyons 1985a,b). After several years of experience, the effective airblast spray rate of ATS was found to be approximately 3.1 L/ha (Byers and Lyons 1985a,b; Byers 1999). The addition of a surfactant did not improve ATS effectiveness. When applied with an airblast sprayer, ATS was most effective when about 70 to 90 percent of the flowers had opened (Byers 1999). ATS burns blossoms and young shoots, especially when applied with certain fungicide tank mixes (Olien et al. 1995). In the case of a long bloom period, one application of ATS was insufficient to cause adequate thinning. Two applications, spaced one to three days apart, and timed at 30 percent open flowers and again at about 95 percent open, substantially increased thinning efficacy (Byers 1999; r. e. Byers unpublished). However, three applications caused substantial shoot injury and defruiting of trees when applied within a five-day flower-opening period (r. e. Byers unpublished). Because of potential defruiting and injury, extreme caution should be used when making multiple applications. A possible explanation for injury is that the chemical degradation between applications is not complete, thus a second or third application might add to the previous chemical deposits on flowers and foliage. Additionally, the rate of chemical degradation as influenced by environmental conditions may vary considerably. Thiourea and/or urea (10 to 12% w/w) applied during bloom resulted in thinning, but applications at the beginning of bud swell and postbloom also caused thinning in early ripening cultivars (Di Marco et al. 1992; Erez 1975). Surfactants. Several surfactants including Dupont WK, Witco SN-50, and Ortho X-77 are effective as bloom thinners (Byers and Lyons 1984a, 1985a,b). Effectiveness is positively correlated with increased phyto-
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
377
toxicity; thus, the initial research involved screening surfactants for phototoxicity. One of the most extensively studied surfactants is a fatty amine polymer called ArmoThin (Akzo Nobel Corp.), which has been tested on several stone fruit species with positive result (Costa et al. 1995; Southwick and Fritts 1995; Costa et al. 1996; Lemus 1996, 1998; Lichou et al. 1996; Southwick et al. 1995a,b; Byers 1999). This compound induces early anther dehiscence, a marked reduction in pollen germination, and reduced pollen tube growth in the stylar tissue soon after germination (Costa et al. 1995). The data on pollen tube growth suggests that the compound was more effective the sooner it was applied after flower opening (Baroni et al. 1995). Application of 2 to 3 percent Armothin when 70 to 80 percent of the flowers have opened has provided good thinning of several different cultivars in several climatic areas. However, much of this work does not report the tree size or chemical rates/ha, both of which influence the deposit and action on the flower (Byers and Lyons 1985a,b).
Desiccating Agents. Endothall (Elf Atochem, Inc.) is among the most promising of this class of chemical bloom thinners and is very effective at very low rates (Byers and Lyons 1984a, 1985a,b). In addition, Wilthin (Entech Corp.) has an EPA registration for use on peach and apple trees in the United States. Our research indicates that a surfactant must be used with this material to be effective (Byers 1999). However, additional testing ofWilthin is needed to determine the necessary rates since recommended label rates frequently may be too low for adequate effectiveness. Dormex (DK International, Inc.) is another promising chemical that is not registered for thinning stone fruit but is currently used for breaking dormancy. Treatment with hydrogen cyanamide (Dormex) or ArmoBreak, after the chilling requirement is met, may stimulate flower bud abscission or inhibit flower opening. As a rule, these chemicals are applied when the chilling requirement is not completely met. Normally, under such conditions, hydrogen cyanamide, nitrogen or surfactant mixtures are applied 40 to 60 days before expected bud-break. In nectarine, applications near to bloom (less than 40 days) may inhibit flower-bud burst (Fallahi et al. 1990). In apricot, application of thiourea, KN0 3 , and Erger D (a mixture of fatty amine polymer and nitrogen compounds) six weeks before the expected bud-break, produced contradictory results. In one case, application of thiourea and KN0 3 increased expected yield but reduced fruit weight (Kuden et al. 1995). In another, Erger D increased bud mortality and fruit weight and response was increased with age of the bearing shoot. These applications also induced early maturity in apricot (Costa et al. 1998).
378
R. BYERS, G. COSTA, AND G. VIZZOTTO
Long Chain Fatty Acids. Pelargonic acid (Thinex-Mycogen Corp.), YI1066 (UAP Corp.), and several other fatty acids are potential bloom thinners because they are sufficiently phytotoxic and short-lived in plant tissues (Klein and Cohen 1995; Fallahi 1997; Byers 1999). Pelargonic acid is currently registered in the United States for stone fruit and apple flower thinning and has been used with some degree of success. In plum, several chemicals including ATS, urea, wettable sulfur, and Dormex, have been tested as bloom thinners. Urea and wettable sulfur have given positive results on several cultivars (Scholtens 1993; Webster and Hollands 1993; Balkhoven-Baart 1997). Dormex acted as a thinner although response differed with cultivar, concentration, and time of application (Fallahi et al. 1992). D. Fruit Thinning 1. Manual Fruit Thinning. Typically, hand-thinning of peach fruits is performed approximately two weeks prior to the pit hardening stage, soon after unfertilized fruit are visually smaller than fertilized fruit. In Italy hand-thinning is normally performed after the pit-hardening stage, when fruits start to grow again and after natural abscission takes place. However, because of the high demand for labor, the short time period when hand-thinning can be performed, and the high cost per tree, alternatives to hand-thinning are universally sought for commercial production (Weinberger 1941; Costa and Vizzotto 2000). Hand-thinning is generally superior to rubber-hose or mechanical shaking methods because the remaining fruits can be better spaced and selected. Knocking fruit from trees with a 40 cm rubber hose can be selective if care is taken to strike the smaller fruit. Mechanical shaking devices remove the largest fruit, thereby reducting mean fruit size, yield, and crop value (Berlage and Langmo 1982; Costa 1978). Limb and whole tree crop loads vary widely following mechanical shaking, due to shaking intensity, limb stiffness, and tree structure. Damage to trees or limbs, equipment cost and availability are also disadvantages.
2. Chemical Fruit Thinning. Chemical fruit thinning is an attractive method for reducing crop load since very little labor is required to perform the practice. However, despite extensive research with many, none has provided satisfactory results (Edgerton and Greenhalgh 1969; Buchanan et al. 1970; Aitken et al. 1972; Costa and Grandi 1974; Costa 1978; Shaybany et al. 1979; Costa and Vizzotto 2000). Furthermore, chemical injury to the tree, leaves, and fruit have been difficult to avoid. Chemical thinning of peach and other stone fruit trees has been considered more difficult than thinning of species such as apple for several
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
379
reasons. Peach flowers open nearly simultaneously; however, cool temperatures may cause the bloom period to differ substantially in length between seasons. In some apple cultivars, a fruiting spur contains a dominant "king" flower that naturally produces the largest fruit and four weaker side flowers. These two categories of flowers, "king" and "lateral," behave distinctly differently. The "king" flowers set a higher percentage of fruit, and the resulting fruit typically contains more seeds than does a lateral fruit. However, most stone fruit species normally develop only one seed per fruit, and each flower has an equal probability for fruit set. In addition, most of the hormone-type chemicals used as apple fruit thinners have been ineffective or have caused either leaf or fruit injury at the concentrations needed to cause stone fruit abscission. In peach, ethephon and other ethylene-generating compounds cause more leaf than fruit abscission, whereas in apple, rates of ethephon (up to 1500 mg/L) which cause leaf or shoot injury may be three to five times higher than those that are required for fruit abscission (300 to 500 mg/L). Auxins [l-naphthaleneacetic acid (NAA) and 1-naphthaleneacetamide (NAAm)] effective on apple typically have been ineffective or have caused fruit abnormalities, leaf abscission, and/or resulted in inconsistent results in Prunus. Since 1970, numerous investigators in several countries have evaluated (2-chloroethyl) phosphoric acid (ethephon) as a chemical fruit thinner for peach and other stone fruits. While some trials have provided positive results, the use of ethephon has not become widespread because of substantial leaf drop and variable thinning related to a number of internal and external factors (Edgerton and Greenhalgh 1969; Stembridge and Gambrell 1971; Costa 1978; Ramina 1981). Factors that may affect response include temperature on the rate of ethylene evolution (Qlien and Bukovac 1978), chemical binding of ethephon to cellular fractions (Lavee and Martin 1974a,b, 1975); fruit versus leaf abscission, fruit load, tree vigor, ratio of vegetative to reproductive sinks, planting density, environmental shading, and nutritional level (Costa and Grandi 1974; Ramina 1981; Costa et al. 1983). In some experiments, inhibitors of GA biosynthesis caused fruit abscission. Paclobutrazol also induced fruit abscission on plum when applied at 1000 or 2000 mg/L at the onset of pit hardening. Full-bloom and later sprays of paclobutrazol were ineffective (Webster and Andrews 1986). Paclobutrazol, a well-known growth retardant for stonefruit, also induces some fruit abscission if applied at the shuck-off stages (about 20 days AFB). However, such sterol inhibitors are not effective on all cultivars and under some growing conditions (Blanco 1987; Marini 1987). In apricot, several different chemicals (NAA, ethephon) and nitrogen compounds have been tested as thinners. NAA was the most effective,
380
R. BYERS, G. COSTA, AND G. VIZZOTTO
but was phytotoxic. Ethephon gave the best results in terms of fruit quantity and had no negative effect on fruits or foliage (Farmahan and Dhiman 1998). NAA and ethephon have been used on plum to induce fruit abscission. Effects were cultivar-, concentration-, and time-specific for each chemical (Webster and Andrews 1986; HarangozQ et aI. 1996). Chemicals that inhibit photosynthesis (e.g., terbacil) cause fruit abscission when applied at least 30 to 40 days AFB (Byers et aI., 1984b; DelValle et aI. 1985), but also cause chlorosis and abscission of leaves. Whole tree shading experiments show that fruit thinning can be achieved without harm to fruit or foliage (Fig. 7.3). E. Chemical Application Technology 1. Chemical Flower Thinning. Typically, recommendations for chemical thinner rates for a block of trees are extrapolated from either handgun dilute sprays to single trees sprayed to the point of drip or airblast sprays applied to trees in a single row. Airblast spray rates that cause thinning to a single row may over-thin when applied to an entire block due to the increased deposit from adjacent row drift. In order to obtain a similar deposit as a single row application (Fig. 7.10AB), a block of trees would need to be sprayed with a reduced rate/ha to obtain similar thinning. At bloom, well-pruned peach trees provide very little barrier for chemical drift to adjacent rows from airblast application, but nonpruned trees may reduce drift substantially (Fig. 7.5ABC). In one test (Fig. 7.10AB), the increased response of peach trees to airblast spray drift of ATS was proportional to the chemical deposit from adjoining rows (Byers and Lyons 1985b). Chemical deposits on peach flowers in adjoining rows were 43 percent of that of those on the sprayed row and the 25 percent on the second row; thus more chemical is deposited by multiple-row spraying than by a spray applied to one row only. If an entire block is sprayed, 68 percent of the deposit was accumulative drift from adjoining rows. Further studies indicated that water rates from 420 to 2338 L/ha did not influence efficacy of ATS if the same chemical rate/ha was used (Byers and Lyons 1985b). However, a handgun sprayer applying 1170 L/ha (Table 7.5) almost defruited the trees, whereas the airblast sprayer resulted in the desired crop load (5.5 FCSA). 2. Fruit Thinning. When chemicals were first tested for apple and/or peach thinning, most were applied with a handgun sprayer at high water volumes; thus, the amounts of chemical and water per hectare were frequently unknown and tree size was not reported. In addition, airblast
7. FLOWER AND FRUIT THINNING OF PEACH AND OTHER PRUNUS
1800
381
A
1600
::::i' 1400 Ol
§. ~ ~ c..
w
1200
1000
C
800
« o :E w
600
.J
~
U1f--------------
400'-Vl-----' 200
o
18 16.514.9
11.39.8 8.2
4.7 3.1 1.5
1.5 3.1 4.7
8.2 9.8 11.3
14.9 16.5 18
DISTANCE FROM SPRAYER (m)
«
4
2 0
o
2
4
6
8
10
12
14
Weeks after full female bloom Fig. 8.10. Cumulative growth of 'Mauritius' lychee fruit, seed, pericarp and aril. (Stern et al. 1995)
First Phase. This phase lasts for about five weeks in Israel and seven to eight weeks in South Africa. At the end of this phase, fruit weight is about 2 g, and is composed mainly of peel (pericarp) (2/3) and seed (1/3). The aril is starting to grow from the base of the seed. The tiny embryo is at the "heart" stage, protruding from the seed coat and it can be seen with the naked eye (Plate 8.6). The remnant of the endosperm may still be present in the seed cavity. Second Phase. This phase lasts for about two weeks in Israel and two to three weeks in South Africa. During this period there is rapid growth of the embryo and the endosperm disappears completely. At the end of this phase, the embryo fills the seed cavity with two well-developed cotyledons, the seed coat has hardened and the aril has started its rapid growth (Plates 8.6 and 8.7). Fruit weight is about 7 g, and is composed of peel (1/3), seed (1/3) and aril (1/3).
436
R. STERN AND S. GAZIT
Third Phase. The last phase lasts for about six weeks in Israel and five to six weeks in South Africa. At the end of this phase, the fruit is ripe, ready for harvest. Fruit weight in Israel is 23 to 24 g, and is composed of peel (1/10), seed (1/10), and edible flesh (aril) (8/10). 4. Fruit Growth Rate. Several studies have determined the growth rate of the fruit and its component tissues (Joubert 1967, 1986; Huang and Xu 1983; Paull et al. 1984; Chaitrakulsub et al. 1988; Stern et al. 1995). The cumulative fresh and dry weights of the whole fruit and its components (pericarp, aril, and seed) follow a sigmoidal growth pattern (Fig. 8.10). The pericarp and the seed reach their maximal fresh weight at about seven weeks, whereas the aril reaches its maximal fresh weight at maturity.
B. Pollen Parent Effect on Seed and Fruit Characteristics
The pollen parent supplies one-half of the seed and one-third of the endosperm genome. These tissues comprise the main portion of the seed; hence, the pollen parent may exert a significant xenic effect on seed characteristics. This phenomenon is well-known in nut crops, where the seed constitutes the harvested product (Sedgley and Griffin 1989). However, it apparently occurs in all crops, but is seldom studied. The embryo and endosperm may exert a significant influence on the fruit maternal tissues (metaxenia). This phenomenon was first found in dates (Nixon 1935; Reuveni 1986), but it is potentially widespread and may be discernible in many other fruit crops. In lychee, several studies have determined the effect of the pollen parent on seed and fruit weights and on the incidence of shriveled seeds with aborted embryos. The identity of the pollen parent was ascertained by either hand-pollination (McConchie et al. 1991; Xiang et al. 2001) or isozyme analysis of the fruit embryo (Stern et al. 1993b; Degani et al. 1995b). From plots with only two cultivars ('Mauritius' and 'Floridian'), selfed and outcrossed embryos were identified by isozyme analysis. Outcrossed fruit were heavier and contained heavier seeds than selfed fruit. This effect was most pronounced for seed weights in selfed 'Floridian' fruit. Discounting the seeds (the xenic effect) still left a clear metaxenic effect, pericarp and aril from outcrossed fruit being heavier than from selfed ones (Stern et al. 1993b; Degani et al. 1995b). Hand-pollination in 'Bengal' with self- and four pollenizer pollens resulted in noticeable differences in fruit weight among the five progeny: one was heavier and two were lighter than the selfed progeny (McConchie et al. 1991), indicating that foreign pollen is not always more effective than self-pollen.
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
437
Lychee fruit may contain a shriveled (chicken tongue) seed, which does not contain a live embryo. Such seeds weigh about 0.5 g, compared to the normal 2 to 4 g (Plate 8.8). Their presence is a great advantage to the consumer because of the higher ratio of flesh to seed. There are great differences among cultivars in the incidence of these desirable fruit. In most, it is quite rare. Only a few (e.g., 'Nuo Mi Ci,' 'Gui Wei,' 'Salathiel') usually have almost only shriveled seeds. Their percentage may change appreciably from year to year and according to locality. Stern et al. (1993b) found a significant positive correlation between the percentage of 'Floridian' fruit with shriveled seeds and the distance to the pollenizer ('Mauritius'). They suggested that self-fertilization in 'Floridian' tends to increase the production of shriveled seeds, probably as a result of inbreeding depression which causes embryo degeneration and abortion. Xiang et al. (2001) hand-pollinated two outstanding cultivars, which usually have a high percentage of shriveled seeds ('Nuo Mi Ci' and 'Gui Wei'), with pollen from several cultivars. They found great differences between the effect of the different pollenizers and the responses of the two pollinated cultivars. 'Nuo Mi Ci' carried a very high percentage (80 to 92%) of fruit with shriveled seeds after pollination with seven pollenizers; however, the use of 'Da Zao' ('Mauritius') pollen resulted in a low percentage (8%) of shriveled-seed fruit. The response in 'Gui Wei' was much more variable: it produced 5, 18, 25, 30,47,65, and 75 percent shriveled-seed fruit after pollination by the seven pollenizers. The lowest percentage was again produced by 'Da Zao' pollen. In Australia, 'Salathiel' ('Southern Cross') produced only shriveled-seed fruit after pollination by five pollenizers (McConchie et al. 1991).
c.
Fruit Abscission
1. Abscission Rate and Pattern. The lychee tree produces a large excess of female flowers. We estimate that a medium-size orchard tree (planted at a spacing of 6 x 6 m) carries about 60,000 female flowers (400 inflorescences, each with about 150 female flowers) (Stern et al. 1993a). At a high yield of 50 kg/tree (14 t ha-1 ), the tree carries about 2,500 mature fruit (20 g each) at harvest. Hence, at best the final fruit set will be only about 4 percent. This simple calculation demonstrates the inevitable massive flower and fruit abscission. Indeed, there are many reports and commentaries dealing with this phenomenon (Mustard et al. 1953; Mustard 1960; Prasad and Jauhari 1963; Chadha and Rajpoot 1969; Hoda et al. 1973; Misra et al. 1973; Pivovaro 1974; Veera and Das 1974; Singh and La11980; Yuan and Huang 1988; McConchie and Batten 1989; Stern et al. 1995, 1997c; Stern and Gazit 1997,1999, 2000b).
R. STERN AND S. GAZIT
438
Most of the massive abscission of flowers and fruitlets occurs during the first month after pollination (Mustard et al. 1953; Joubert 1986; Stern et al. 1995, 1997c; Stern and Gazit 1999). In Israel, by the fifth week after pollination, about 90, 96, and 99 percent of all female flowers abscised in 'Mauritius,' 'Floridian,' and 'Kaimana,' respectively (Fig. 8.11). Apparently, most of the abscised flowers are not fertilized, due to inadequate pollination, nonviable pollen, problems in the fertilization process and defective ovules (Mustard et al. 1953; Mustard 1960; Joubert 1986; McConchie and Batten 1989; Stern and Gazit 1996, 1998). It is difficult to determine the effect of each of these factors, but in Israel, the last factor bears the major responsibility: most of the female flowers are abnormal, in that they lack an embryo sac, egg apparatus, and/or polar nuclei (Stern et al. 1996b, 1997a).
100 . - - - - - - - - - - - - - - . . ,
C)
c:
'S:
.~
::s
t/)
::
::s 10
.....s-
..... 0 ..... c: a>
Mauritius
(,)
s-
a>
Q.
Floridian
--.__--I~I--__...
b
Kaimana
o
2
4
6
8
10
12
14
Weeks after full female bloom Fig. 8.11. A typical fruit-drop pattern in 'Kaimana,' 'Mauritius,' and 'Floridian' lychee. Each value is the average of 12 inflorescence from uniform trees. Mean separation at harvest by Duncan's multiple range test, P = 0.05. (Stern and Gazit 1999)
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
439
Two distinct abscission periods, with minor variations, were found in 'Mauritius' (Fig. 8.11) (Stern et al. 1995). The first period lasts for about a month, at the end of which 5 to 10 percent of the female flowers survive to develop into small fruitlets. The second abscission wave begins one or two weeks later, lasting for about two weeks. Fruitlets that abscise at this stage weigh 2 to 6 g, and contain a well-developed seed coat. Rapid embryo growth consistently coincided with the second abscission period (Fig. 8.12). The abscission subsides when the embryo has reached full size. During the second period, about half the remaining fruitlets abscise. Hence, only 2 to 5 percent of the initial female flowers develop into mature fruit. Fruit-drop intensity varies according to cultivar, environmental conditions, and cultural practices. It is not rare to find that all fruit of a given panicle have abscised before harvest. In Israel, 'Kaimana' tends to shed almost all its fruitlets in the third and fourth week after fruit set (Fig. 8.11). Initial set by the fourth week was only 4 percent, two weeks later reaching the low final set of about 1 percent. No distinct abscission waves could be discerned (Stern and Gazit 1999). 'Floridian,' on the other hand, exhibits two abscission waves like 'Mauritius'; however, this cultivar tends to retain more fruitlets at the end of the first wave (10 to 20%), but to drop most of them during the second wave, with a final set of 1 to 3 percent (Stern 1992; Stern et al. 1997c). 100
-..-.------------.-3
~
ii .~
c:
... ::::s
II)
10
Cl)
E
2 u. II
o
2
4
6
8
10
12
Weeks after full female bloom Fig. 8.12. A typical patterns of 'Mauritius' lychee fruitlet abscission and seed growth in Israel during 1988. Initial numbers offemale flowers per inflorescence was about 160. Each value is an average of 12 replicates. (Stern et al. 1995)
440
R. STERN AND S. GAZIT
In China, abscission patterns were studied in the normal seeded 'Huai Zhi' and the aborted-seeded 'Nuo Mi Ci' (Yuan and Huang 1988; Wang and Qiu 1997; Huang 2001). They usually found multiple waves, up to three in 'Huai Zhi' and up to five in 'Nuo Mi Ci.' However, there were significant differences among years. In both cultivars, most of the abscission occurred during the first month, in one or two waves. In the seeded cultivar an additional wave occurred during the sixth and seventh weeks and then stopped (similar to the results with seeded cultivars in Israel). In contrast, the aborted seed cultivar had an additional pronounced wave much later, in the ninth week (close to harvest). 2. Abscission Reduction with Plant Growth Regulators. In a large number of fruit crops, including citrus, apples, pears, and peaches, fruitlet abscission can be reduced or prevented by auxin application (Leopold 1958; Weaver 1972; Arteca 1996). Fruit abscission is facilitated by the action of the hydrolytic enzymes polygalacturonase and cellulase, which cause degradation of the cell wall and middle lamella in the abscission zone. Ethylene promotes their synthesis and activity, whereas auxin delays these processes (Goren 1993). Liu (1986) found that the endogenous indolacetic acid (IAA) content in lychee fruitlets rises steeply during the first three weeks of fruit development, from 150 to 850 ~g g-1 FW, but decreases after the onset of rapid embryo development, four to five weeks after fertilization, falling to 300 ~g g-1. Many studies on the effect of various growth regulators on lychee initial and final fruit set were reported from India, especially in the 1970s. These started with Prasad and ]auhari's (1963) report on great increases in fruitlet retention and yield on panicles sprayed with naphthaleneacetic acid (NAA) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 35 to 100 mg L-1, with a concurrent increase in fruit size. The following studies were also conducted, on a rather small scale, at the panicle level, or on tree parts. A large assortment of growth regulators was sprayed in addition to NAA and 2,4,5-T. Most were reported to reduce fruit drop, sometimes significantly. Khan et al. (1976) stated that NAA at 20 mg L-1, 2,4,5,-T at 10 mg L-1, gibberellic acid (GA 3 ) at 100 mg L-1 and 2 cloroethyl trimethyl ammonium chloride (CCC) at 250 mg L-1, check fruit drop significantly. Hoda et al. (1973) reported that NAA at 10 mg L-1 and 2,4-dichlorophenoxyacetic acid (2,4-D) at 15 mg L-1, especially in combination with a prior spray of zinc sulfate at 1 percent, have a significant positive effect on fruit retention. Singh and Lal (1980) concluded that GA 3 at 50 mg L-1 increases fruit retention. A number of other studies also produced positive results (Veera and Das 1974; Verma et al. 1980; Yuan and Huang 1991), whereas others failed to reduce
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
441
abscission (Misra et al. 1973; Singh and Dhillon 1981). However, the successful reports were not followed up with larger-scale studies at the tree and orchard levels, in order to arrive at a reliable method that could be recommended for use. The fact that the use of growth regulators for the reduction of fruitlet drop is not recommended in India (Pandey and Sharma 1989) reflects this situation. Several studies conducted in Israel did not verify the ability of NAA, 2,4,5-T or GA 3 to reduce lychee fruit drop (Pivovaro 1974; Shalem-Galon 1980; Stern et al. 1995). The contradiction with the positive reports from India and China may be the result of genetic differences between cultivars, environmental conditions, or the timing of the synthetic auxin application. It is also possible that differences in the formulation of the sprayed substances affected their efficacy. In Israel, Pivovaro (1974) found that the auxin 2,4,5-trichlorophenoxypropionic acid (2,4,5-TP), at 50 to 400 mg L-1, is consistently effective at reducing lychee fruit drop. The commercial product he used (Tipimon) is a liquid solution, containing 6.8 percent 2,4,5-TP, formulated as a triethanolamine salt. However, most of the resulting mature fruit was seedless, very small, with no market value. In another study, Tipimon failed to reduce fruit drop when applied seven to eight weeks after fruit set (Shalem-Galon, 1980). Later, Stern et al. (1995) found that timing is critical: spraying 'Mauritius' is effective only when executed about five weeks after peak female bloom, when fruitlet weight is about 2 g (Plate 8.6). At this stage, the embryo begins its rapid growth, followed, a few days later, by a second wave of fruit drop (Fig. 8.12). Fruitlet drop was consistently and significantly reduced and yield increased by spraying at that stage. The first success at the panicle level was followed by successful spraying at the tree level and then at the orchard level (Stern 1992; Stern et al. 1995). Based on this study, it has been recommended that mature 'Mauritius' orchards be sprayed at the 2 g stage with 100 mg L-1 2,4,5-TP (0.15% Tipimon) at 1000 L ha-1. 'Floridian' responded in a similar manner but the timing was less critical: it could also be sprayed about four weeks after fruit set, when fruitlet weight is about 1 g (Stern et al. 1997c). These recommendations have been adopted by the lychee industry in Israel. It should be noted that this spray might cause some foliar scorching, especially if spraying volume is excessive. 'Floridian' is more susceptible than 'Mauritius,' and 'Kaimana' is even more so. Spraying with 2,4,5-TP caused an increase in fruit with shriveled seeds in 'Mauritius,' and particularly in 'Floridian' (Stern et al. 1995, 1997c). This indicates that this treatment can reduce the abscission of fruitlets with degenerate or aborted embryos.
442
R. STERN AND S. GAZIT
Stern and Gazit (1997) tested a large number of synthetic auxins, in search of an alternative to 2,4,5-TP. The synthetic auxin 3,5,6-trichloro2-pyridyl-oxyacetic acid (3,5,6-TPA), as formulated in the commercial product Maxim® (manufactured by Dow AgroSciences, and sold as tablets containing 10% a.i.) was effective at 50 mg L-1 at reducing fruitlet abscission in 'Mauritius.' It was also very effective in 'Kaimana,' but only when sprayed early, about three weeks after fruit set, when fruit weight is about 0.5 g (Stern and Gazit 1999). Almost all this later cultivar's fruitlets are shed during the fourth week after fruit set (Fig. 8.11), hence a later treatment cannot be effective. In contrast, Maxim was found to be ineffective with 'Floridian' (Stern et a1. 2000). Preliminary trials in China found significant increases in yield by spraying young trees of 'Hei Ye' and 'Fei Zi Xiao' with Tipimon and Maxim (Stern et a1. 2001). In none of the trials with Maxim spraying was any foliar scorching observed. Spraying with 3,5,6-TPA resulted in a significant increase (14 to 30%) in fruit weight in 'Mauritius,' 'Floridian,' 'Kaimana,' 'Hei Ye' and 'Fei Zi Xiao' (Stern and Gazit 1999; Stern et a1. 2000, 2001). This increase occurred concomitantly with a much higher increase in yield. Hence, the increase in fruit number was the main factor for the yield increase. Obviously, the increase in fruit size cannot be explained by fruit thinning, as suggested for citrus (Zaragoza et a1. 1992) and apple (Dennis 1986). The treatment probably makes the fruit a stronger sink (Agusti et a1. 1995). The concomitant significant increase in lychee seed weight (Stern et a1. 2000) apparently reflects this effect. The aril's TSS (total soluble solids) level did not decrease with the pronounced yield increase, indicating that the higher crop load had not exhausted the tree's capacity. Recently, Stern et al. (2000) found the highest yield in 'Mauritius' and 'Floridian' after spraying with 2,4,5-TP at 67 mg L-1 (0.1 % Tipimon) and about one week later with Maxim (3,5,6-TPA at 20 mg L-1). The increased yield was apparently the result of a reduction in fruitlet drop (by both auxins) and increased fruit weight (by the second, 3,5,6-TPA treatment). The combined treatment is now used on a commercial scale in Israel. In conclusion, the two synthetic auxins (2,4,5-TP and 3,5,6-TPA), as formulated in two commercial products (Tipimon and Maxim, respectively), were found to greatly reduce lychee fruitlet abscission and increase yield (Stern and Gazit 2000b). Both auxins are now routinely applied in commerciallychee orchards in Israel. However, other lychee cultivars might respond differently; hence, a tailor-made protocol should be determined for each cultivar. The environment might also affect the
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
443
response to auxin sprays. Thus, in other countries, detailed trials should be conducted for each cultivar, in order to realize the potential of auxins to significantly increase lychee yield. VI. CONCLUDING REMARKS
In lychee, as in other crops, we strive to reach the highest sustainable yield of high-quality fruit. The highest sustained yield for which we have reliable data is about 20 t ha-1 (four-year average for 'Mauritius,' at Lavi orchard, Israel). The fact that fruit weight did not decrease in this orchard indicates that we have not yet reached the commercial yield limit. We estimate that under optimal growing conditions, a sustainable yield of 25 t ha- 1 can be achieved. Many factors are responsible for the rather low yield of 5 to 10 t ha-1 in most of the world's lychee orchards. In this chapter, only those factors related to reproductive biology were covered, assuming that the trees are healthy and well-maintained. Our knowledge and understanding of most aspects of lychee fruit formation has greatly expanded over the last 20 years, with most of the work having been conducted in Australia, Israel, and China. Note that most of the Chinese findings have been inaccessible to the English-speaking world. In our concluding remarks, we will try to highlight the significant advances achieved and the subjects that merit more study in order to realize lychee's yield potential. 1. Fruit Bud FOrInation. Inadequate flowering is sometimes the main limiting factor in obtaining a good lychee yield. It is mainly a problem where the winter is not cold enough and the environmental conditions promote late autumnal vegetative flushes. Breeding and selection of high-quality cultivars, under warm winter conditions, is the best longterm solution for the low-elevation tropicallychee industry. Judicious use of water and/or nutritional stress has been able to prevent autumnal vegetative flushes, ensuring adequate blooming. However, these methods are often not feasible. The use of growth retardants might eventually provide an effective solution in those cases.
2. Normal Female and Male Reproductive Organs. There is likely a widespread problem of defective pollen and even more so ovules in lychee. In Israel, where this aspect was studied, most of the flowers were found to be infertile, with ovaries that did not contain even one normal ovule. There are apparently great differences among cultivars and environmental factors that are also involved. Much more research should be conducted into the factors responsible for the impaired functionality of
444
R. STERN AND S. GAZIT
the pollen and ovules. A prerequisite for high yield is an adequate number of flowers with at least one normal ovule.
3. Pollination. Though wind may playa role in lychee pollination, effective insect vectors are essential for adequate pollination. The lychee bloom, especially the female one, is attractive to honeybees and other effective pollinators. Thus, during the female lychee bloom there is usually strong pollinator activity. In addition to pollinators, available viable pollen is also needed. There is usually a partial overlap between the female and male blooms. However, the presence of another cultivar, which has a male bloom (preferably the potent M z) during the first cultivar's peak female bloom, may improve pollination by ensuring the presence of available pollen throughout the female bloom. 4. The Fertilization Process. Rain and hot weather have deleterious effects on pollen germination and the fertilization process. No solution has yet been devised to these weather-related problems.
5. Fruit Set. Putrescine spraying at the female bloom had a pronounced positive effect on yield. We do not know how this effect was achieved. It may be the result of prolonging the effective pollination period, through delayed senescence of the pistil. Thus, the extended bloom of fully mature female flowers coincides with the potent M z bloom. However, an entirely different mechanism may be responsible. 6. Fruit Drop. Massive drop of fruitlets that have the capacity to develop into full-size fruits is a typical undesirable phenomenon in lychee. Spraying with two synthetic auxins (2,4,5-TP and 3,5,6-TPA) produced a significant reduction in fruit drop and subsequently, a great increase in yield in several cultivars. The use of these and other auxins will probably also be effective in reducing fruitlet drop in many other cultivars. However, the successful use of this method depends on its calibration for each cultivar. We envision the breeding and selection of parthenocarpic seedless lychee cultivars in this century. Most of the problems mentioned and discussed in this chapter will no longer be relevant when such cultivars are developed. However, until that time, we hope that this chapter will be instrumental in solving pressing problems related to lychee reproductive biology and in increasing lychee yields throughout the world. LITERATURE CITED Acta Hart. Number 558. Proc. 1st Intnl. Symp. litchi and longan. 2001. (H. Huang and C. Menzel, Eds.), Guangzhou, China.
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
445
Agusti, M., M. EI-Otmani, M. Aznar, M. Juan, and V. Almela. 1995. Effect of 3,5,6-trichloro2-pyridyl-oxyacetic acid on clementine early fruitlet development on fruit size at maturity. J. Hort. Sci. 70:955-962. Alexander, M. P. 1969. Differential staining of aborted, and nonaborted pollen. Stain Technol. 44:117-122. Apelbaum, A., A. C. Burgoon, J. D. Anderson, and M. Lieberman. 1981. Polyamines inhibit biosynthesis of ethylene in higher plant tissue, and protoplasts. Plant Physiol. 68:453-456. Argaman, E. 1983. Effect of temperature, and pollen source on fertilization, fruit set, and abscission in avocado (Persea americana Mill.). (in Hebrew). MS Thesis, Hebrew Univ. Jerusalem, Israel. Arteca, R. N. 1996. Plant growth substances: principles and applications. Chapman and Hall Press, New York. Baker, H. G., and I. Baker. 1983. Floral nectar sugar constituents in relation to pollination type, p. 117-141. In: C. E. Jones and K. J. Little (eds.), Handbook of experimental pollination biology. Van Nostrand Reinhold Co., New York. Banerji, I., and K. 1. Chaudhuri. 1944. A contribution to the life-history of Litchi chinensis Sonn. Proc. Indian Acad. Sci. Section B, 19:19-27. Barker, R. J., and Y. Lehner. 1974. Acceptance, and sustenance value of naturally occurring sugars fed to newly emerged adult workers of honeybees (Apis mellifera L.). J. Expt. Zool. 187:277-286. Batten, D. J. 1982. Lychee. In: C. Hacket and J. Carolane (eds.). Edible horticultural crops: a compendium of information on fruits, vegetables, spice, and nut species. Crop number 550. Academic Press, Sydney. Batten, D. J. 1986. Towards an understanding ofreproductive failure in lychee (Litchi chinensis Sonn.). Acta Hort. 175:79-83. Batten D. J., and C. A. McConchie. 1992. Pollination in lychee. Proc. 3rd Natl. Lychee Seminar Bundaberg, Australia, p. 23-28. Batten, D. J., and C. A. McConchie. 1995. Floral induction in growing buds oflychee (Litchi chinensis), and mango (Mangifera indica). Austral. J. Plant Physiol. 22:783-791. Burgos, L., and J. Egea. 1993. Apricot embryo-sac development in relation to fruit set. J. Hort. Sci. 68:203-208. Burgos, L., T. Berenguer, and J. Egea. 1995. Embryo-sac development in pollinated, and non-pollinated flowers of two apricot cultivars. J. Hort. Sci. 70:35-39. Butcher, F. G. 1956. Bees pollinate lychee blooms. Proc. Fla. Lychee Growers Assoc. 3:59-60. Butcher, F. G. 1957. Pollinating insects on lychee blossoms. Proc. Fla. Stat. Hort. Soc. 70:326-328. Campbell, C. W. 1994. Lychee cultivars in Florida: past, present, and future. Proc. Fla. State Hort. Soc. 107:347-348. Campbell, C. W., and S. E. Malo. 1968. The Lychee. Fruit crops fact sheet 6. Florida Coop. Ext. Serv., Gainsville, F1. Campbell, R. J. 1994. Fall pruning induces blooming in young lychee trees. Proc. Fla. State Hort. Soc. 107:348-350. Chadha, K. L., and M. S. Rajpoot. 1969. Studies on floral biology, fruit set, and its retention, and quality of some lychee varieties. Indian J. Hort. 26:124-129. Chaikiattiyos, S., C. M. Menzel, and T. S. Rasmussen. 1994. Floral induction in tropical fruit trees: effects of temperature, and water supply. J. Hort. Sci. 69:397-415. Chaitrakulsub, T., P. Chaidate, and H. Gemma.1988. Study of fruit development of Litchi chinensis Sonn. var. Hong-Huay. Japanese J. Tropical Agr. 32:201-207.
446
R STERN AND S. GAZIT
Chaitrakulsub, T., R Ogata, S. Subhadrabandhu, S. Powsung, and H. Gemma. 1992a. Effect of paclobutrazol on vegetative growth, flowering, fruit set, fruit drop, fruit quality, and yield of lychee cv. Hong Huay. Acta Hort. 321:291-299. Chaitrakulsub, T., R Ogata, S. Subhadrabandhu, S. Powsung, and H. Gemma. 1992b. Use ofpaclobutrazol, and ethophen in influencing flowering, and leaf flushing oflychee cv. Hong Huay. Acta Hort. 321:309-317. Chapman, K. R 1984. Lychee. p. 179-191. In: P. E. Page (ed.). Tropical tree fruit for Australia. Queensland Dept. Primary Industries, Brisbane, Australia. Chapman, K. R, B. Paxton, and B. W. Cull. 1980. Litchi cultivar evaluation (Project 1). Bienn.Rep. Maroochy Hort. Res. Sta. 2:32-33. Chaturvedi, R B. 1965. Preliminary studies in the sex distribution, pollination, and fruit development in litchi (Litchi chinensis Sonn.). Allahabad Farmer 39:49-51. Chaturvedi, R B., and G. K. Saxena. 1965. Studies on the blossom biology oflitchi (Litchi chinensis Sonn.). Allahabad Farmer, 39:10-13. Chen, H., and H. Huang. 2001. China litchi industry: development, achievements, and problems: Acta Hort. 558:31-39. Chen, W. S. 1990. Endogenous growth substances in xylem, and shoot tip diffusate of lychee in relation to flowering. HortScience 25:314-315. Chen, W. S., and M. L. Ku. 1988. Ethephon, and kinetin reduce shoot length, and increase flower bud formation in lychee. HortScience 23:1078. Chen, Y. 1993. Apiculture in China. Agricultural Pub. House, China. Cobin, M. 1954. The lychee in Florida. Bul. Florida Agr. Expt. Sta. 546:1-35. Costes, E. 1988. Analyze architecturale et modelisation du litchi (Litchi chinensis Sonn.). PhD diss., Univ. of Montpellier, France. Crane, E. 1990. Bee and beekeeping: Science practice, and world resources. Heinemann Newnes, Oxford. Crane, J. [date]. Personal communication. Das, C. S, and K. R Choudhury. 1958. Floral biology of litchi (Litchi chinensis Sonn.) S. Indian Hort. 6:17-22. Davenport, T. 1., Y. Li, and Q. Zheng. 1999. Toward reliable flowering of lychee (Litchi chinensis Sonn.) in South Florida. Proc. Fla. State Hort. Soc. 112:182-184. De Candolle, A. 1964. Origin of cultivated plants (Reprint of 2nd ed. 1886). Hafner, New York. Degani, c., A. Beiles, R EI-Batsri, M. Goren, and S. Gazit. 1995a. Identifying lychee cultivars by isozyme analysis. J. Am. Soc. Hort. Sci. 120:307-312. Degani, c., R A. Stern, R EI-Batsri, and S. Gazit. 1995b. Pollen parent effect on the selective abscission of Mauritius, and Floridian lychee fruits. J. Am. Soc. Hort. Sci. 120: 523-526. Dennis, F. G., Jr. 1986. Apple, p. 1-44. In: S. P. Monselise (ed.). Handbook of fruit set, and development. CRC Press, Boca Raton, FL. Dhaliwal, H. S., S. Srivastava, and R. 1. Adlakha. 1977. Insect pollination oflychee, Litchi chinensis Sonn., in the valley areas of the Indian Himalayas. Proc. 26th IntI. Apic. Congo Adelaide, 396. Apimondia Publ. House, Bucharest. Du Toit, A. P. 1994. Pollination ofavocados, mangoes, and litchis. Plant Protection News, Bul. Plant Protection Res. Inst. (South Africa) 35:4-5. Eaton, G. W. 1959. A study of the megagametophyte in Prunus avium, and its relation to fruit setting. Canadian J. Plant Sci. 39:466-476. Fahn, A. 1990. Plant anatomy (4th ed.), Pergamon Press, New York. Faust, M., and S. Y. Wang. 1992. Polyamines in horticulturally important plants. Hort. Rev. 14:333-356. Fivaz, J., and P. J. Robbertse. 1995. Possible pollination factors causing fruit drop in litchi (Litchi chinensis Sonn.) Yrbk. S. African Litchi Growers' Assoc. 7:26-30.
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
447
Fivaz, J., P. J. Robbertse, and S. Gazit. 1994. Studies on the morphology, viability, and storage of pollen grains of litchi (Litchi chinensis Sonn.). Yrbk. S. African Litchi Growers' Assoc. 6:9-12. Free, J. B. 1993. Insect pollination of crops. 2nd ed. Academic Press, London. Furokawa, Y., and M. J. Bukovac. 1989. Embryo sac development in sour cherry during the pollination period as related to fruit set. HortScience, 24:1005-1008. Galan-Sauco, V. 1989. Litchi cultivation. FAO, Plant production, and protection, paper 83, Rome. Gazit, S. 1996. Mango, lychee, and anona cultivation. (in Hebrew) Alon Hanotea. 50:63-66. Gazit, S., and M. Goren. 1997. Litchi culture in China. (in Hebrew) Alon Hanotea 51:86-91. Goren, M. 1990. High density litchi orchards by reducing tree height. (in Hebrew) Alon Hanotea 44:699-708. Goren, M., O. Degani, and S. Gazit. 1998. Flowering phenology of 10 lychee cultivars in the Volcani center, Israel. (in Hebrew) Alon Hanotea 52:59-63. Goren, M., and S. Gazit. 1993. Small-statured litchi orchards: a new approach to the growing of litchi. Acta Hort. 349:69-72. Goren, M., and S. Gazit. 1996. Management of lychee orchards in Israel. Proc. 4th Natl. Lychee, and Longan Sem. Yepoon, Australia. Goren, R. 1993. Anatomical, physiological, and hormonal aspects of abscission in citrus. Hort. Rev. 15:145-182. Gosh, S. P. 2001. World trade in litchi: past, present, and future. Acta Hort. 558:23-30. Groff, G. W. 1921. The lychee, and lungan. Orange Judd Company, and Canton Christian College, China. Groff, G. W. 1943. Some ecological factors involved in successfullychee culture. Proc. Fla. State Hort. Soc. 56:134-155. Groff, G. W. 1948. Additional notes upon the history of the Brewster lychee. Proc. Fla. State Hort. Soc. 61:285-289. He, D. P. 2001. An overview of integrated management of insect pests in litchi orchards of Guangdong. Acta Hort. 558:401-405. Heinrich, B. 1983. Insect foraging energetics, p. 187-214. In: E. C. Jones and R. T. Little (eds.), Handbook of experimental pollination biology. Van Nostrand Reinhold Co., New York. Hoda, M. N., N. B. Syamal, and V. S. Chhonkar. 1973. Effect of growth substances, and zinc on litchi fruit drop. Indian J. Hort. 30:456-460. Huang, H. 2001. Towards a better insight into the development ofthe arillate fruit of litchi, and longan. Acta Hort. 558:185-192. Huang, H., and Y. X. Qiu. 1987. Growth correlations, and assimilate partitioning in the arrilate fruit of Litchi chinensis Sonn. Austral. J. Plant Physiol. 14:181-188. Huang, H., and J. XU. 1983. The development patterns of fruit tissues, and their correlative relationships in Litchi chinensis Sonn. Scientia Hort. 19:335-342. Joubert, A. J. 1967. Die bloei, embriosak-, embrio-en verugontwikkeling von Litchi chinensis Sonn. cultivar HLH Mauritius. MS Thesis, Univ. Witwatersrand, Johannesburg, South Africa. Joubert, A. J. 1985. Litchi chinensis. Vol. 5. p. 204-210. In: A. H. Halevy (ed.), Handbook of flowering. CRC Press, Boca Raton, FL. Joubert, A. J. 1986. Litchi. p. 233-246. In: S. P. Monselise (ed.), Handbook of fruit set, and development, CRC Press, Boca Raton, FL. Kadman, A., and E. Slor. 1982. Litchi growing in Israel. (in Hebrew) Alon Hanotea, 36:673-688. Khan, I., R. S. Misra, and R. P. Srivastava. 1976. Effect of plant growth regulators on the fruit drop, size, and quality of litchi cultivar Rose Scented. Prog. Hort. 8:61-69. Khan, K. S. 1929. Pollination, and fruit formation in litchi. Agr. J. India 24:183-187.
448
R. STERN AND S. GAZIT
King, J., E. M. Exley, and V. Vithange. 1989. Insect pollination for yield increases in lychee, p. 142-145. In: D. J. Batten (ed.), Proc. 4th Austral. conf. tree nut crops. Exotic Fruit Growers Assn., Lismore, Australia. Knight, R. J. 1980. Origin, and world importance oftropical, and subtropical fruits crops. p. 1-120. In: S. Nagy, and P. E. Shaw (eds.), Tropical, and subtropical fruits: composition, properties, and uses. AVI, Westport, CT. Knight, R. J. 2001. The lychee's history, and current status in Florida. Acta Hort. 558:41-44. Kumar, D. 1979. Some aspects ofthe physiology of Coffea arabica 1.: a review. Kenya Coffee 44:9-46. Leopold, A. C. 1958. Auxin uses in the control of flowering, and fruiting. Annu. Rev. of Plant Physiol. 9:281-310. Levit, J. 1980. Chilling, freezing, and high temperature stress, p. 347-470. In: J. Levit (ed.), Responses of plants to environmental stress. Academic Press, New York. Li, c., and Y. Xiao. 2001. Girdling increases yield of Nuomici litchi. Acta Hort. 558:233-235. Li, J. 1997. Diseases, and pests, and their control. p. 140-161. In: Z. W. Zhang, P. Y. Yuan, B. Q. Wang, Y. P. Qiu, and J. S. Li. (eds.), Litchi, pictorial narration of cultivation. Pomology Res. Inst., Guangdong Acad. Agr. Sci., Guangzhou, China. Li, Y. c., T. 1. Davenport, R. Rao, and Q. Zheng. 2001. Nitrogen, flowering, and production of lychee in Florida. Acta Hort. 558:221-224. Liang, G. ]., and G. X. Yu.1991. Effect ofPP333 on mature, non-flowering, and leaflet-onpanicle litchi trees. Scientia Hort. 48:319-322. Liang, W. Y., 1. F. Liang, Z. 1. Ji, and P. W. Li. 1987. The fluctuation of endogenous gibberellin, and indol-3-acetic acid in litchi chinensis shoot-tips during floral initiation. Acta Hort. Sinica. 14:145-152. Liu, J. 1986. Studies on the changes of endogenous indoleacetic acid, and gibberellin during litchi fruit development. MS Thesis. South China Agr. Univ., Guangzhou. Liu, S. Y. 1954. Studies of Litchi chinensis Sonn. PhD diss. Univ. Michigan, Ann Arbor, MI. Marloth, R. H. 1947. The litchi in South Africa. Farming S. Africa 22:823-830. McConchie, C. A., and D. J. Batten. 1989. Floral biology, and fruit set in lychee. Proc. 2nd Natl. Lychee Seminar, Cairns, Australia 71-74. McConchie, C. A., and D. J. Batten. 1991. Fruit set in lychee (Litchi chinensis Sonn.). Variation between flowers, panicles, and trees. Ausral. J. Agr. Res. 42:1163-1172. McConchie, C. A., D. J. Batten, and A. Vivian-Smith. 1991. Pollination in lychee. Austral. Lychee Yrbk. 1:93-96. McGregor, S. E. 1976. Insect pollination of cultivated crop plants. U.S. Dept. Agr. Agr. Res. Ser. 496 p. 247-248. McMillan, R. T. 2000. Plant pathogens commonly found on Litchi chinensis in South Florida. 1st Intl. Symp. litchi, and longan. Guangzho, China, p. 73 (Abstr. E-01). Menzel, C. M. 1983. The control of floral initiation in lychee: a review. Scientia Hort. 21:201-215. Menzel, C. M. 1984. The pattern, and control of reproductive development in lychee. A review. Scientia Hort. 22:333-345. Menzel, C. M. 2001. The physiology of growth, and cropping in lychee. Acta Hort. 558:175-184. Menzel, C. M., and B. F. Paxton. 1986a. The effect of cincturing at different stages of vegetative flush maturity on the flowering of litchi (Litchi chinensis Sonn.). J. Hort. Sci. 61:135-139. Menzel, C. M., and B. F. Paxton. 1986b. Effect of cincturing on growth, and flowering of lychee: preliminary observations in subtropical Queensland. Austral. J. Expt. Agr. 26:255-259.
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
449
Menzel, C. M., and D. R. Simpson. 1987. Effect of cincturing on growth, and flowering of lychee over several seasons in subtropical Queensland. Austral. J. Expt. Agr. 27:733-738. Menzel, C. M., and D. R. Simpson. 1988. Effect of temperature on growth, and flowering of litchi (Litchi chinensis Sonn.) cultivars. J. Hort. Sci. 63:347-358. Menzel, C. M., and D. R. Simpson. 1990a. Does paclobutrazol have role in lychee cultivar? Acta Hort. 275:205-210. Menzel, C. M., and D. R. Simpson. 1990b. Performance, and improvement oflychee cultivars: a review. Fruit Var. J. 44:197-215. Menzel, C. M., and D. R. Simpson. 1991. Effect of temperature, and leaf water stress on panicle, and flower development of litchi (Litchi chinensis Sonn.). J. Hort. Sci. 66:335-344. Menzel, C. M., and D. R. Simpson. 1992. Flowering, and fruit set in lychee (Litchi chinensis Sonn.) in subtropical Queensland. Austral. J. Expt. Agr. 32:105-111. Menzel, C. M., and D. R. Simpson. 1994. Lychee. p. 123-145. In: B. Schaffer, and P. C. Anderson (eds.). Handbook of environment physiology of fruit crops. Vol. 2. Subtropical, and tropical crops. CRC Press, Boca Roton, FL. Menzel, C. M., and D. R. Simpson. 1995. Temperatures above 20°C reduce flowering in lychee (Litchi chinensis Sonn.). J. Hort. Sci. 70:981-987. Menzel, C. M, M. L. Carseldine, and D. R. Simpson. 1988b. Crop development, and leaf nitrogen in lychee in subtropical Queensland. Austral. J. Expt. Agr. 28:793-800. Menzel, C. M., M. L. Carseldine, G. F. Haydon, and D. R. Simpson. 1992. A review of existing, and proposed new leaf nutrient standards for lychee. Scientia Hort. 49:33-53. Menzel, C. M., T. Olesen, and C. A. McConchie, 1999. Making a profit from lychee in Australia. Proc. 5th Natl. Lychee Conference, Twin Waters. Australia, p. 5-15. Menzel, C. M., T. S. Rasmussen, and D. R. Simpson. 1989. Effects oftemperature, and leaf water stress on growth, and flowering of litchi (Litchi chinensis Sonn.). J. Hort. Sci. 64:739-752. Menzel, C. M., K R. Chapman, B. F. Paxton, and D. R. Simpson. 1986. Growth, and yield oflychee cultivars in subtropical Queensland. Austral. J. Expt. Agr. 26:261-265. Menzel, C. M., J. H. Oosthuizen, D. J. Roe, and V. J. Doogan. 1995. Water deficit at anthesis reduce CO 2 assimilation, and yield of lychee (Litchi chinensis Sonn.) trees. Tree Physiol. 15:611-617. Menzel, C. M, B. J. Watson, and D. R. Simpson. 1988a. The lychee in Australia. Queensland Agr. J. 114:19-26. Milne, D. L. 1999a. Lychee production, and research in Southern Africa. Proc. 5th Natl. Lychee Conference, Twin waters, Australia, p. 25-31. Milne, D. L. 1999b. Logistic of growing, and marketing lychee in South Africa. Proc. 5th Natl. Lychee Conference, Twin waters, Queensland, Australia, p. 77-81. Misra, S. K, J. P. Nauriyal, and R. P. Awasthi. 1973. Effect of growth regulators on fruit drop in litchi. Punjab Hort. J. 13:122-126. Mitra, S. K, and D. Sanyal. 1990. Effect of putrescine on fruit set, and quality of litchi. Gartenbauwissenschaft, 55:83-84. Moncur, M. W. 1988. Floral development of tropical, and subtropical fruit, and nut species. C.S.I.R.O., Division of Water, and Land Resources, Australia. Moss, G. I. 1969. Influence of temperature, and photoperiod on flower induction, and inflorescence development in sweet orange (Citrus sinensis L. Osbeck). J. Hort. Sci. 44:311-320. Mulcahy, G. B., and D. L. Mulcahy. 1985. Ovarian influence on pollen tube growth, as indicated by the semivivo technique. Am. J. Bot. 72:1078-1080. Mustard, M. J. 1960. Megagametophytes ofthe lychee (Litchi chinensis Sonn.), Proc. Am. Soc. Hort. Sci. 75:292-304.
450
R. STERN AND S. GAZIT
Mustard, M. J., S. Liu, and R. Q. Nelson. 1953. Observations of floral biology, and fruit setting in lychee varieties. Proc. Fla. State Hort. Soc. 66:212-220. Mustard, M. J., R. O. Nelson, and S. Goldweber. 1956. Exploratory study dealing with the effect of growth regulators, and other factors on the fruit production of the lychee. Proc. Florida Lychee Growers. Assoc, 3:33-38. Nadler, M. 1995. Flowering, pollination, and fruitlet abscission in the litchi. (in Hebrew) MS Thesis, Hebrew Univ. Jerusalem, Israel. Nakata, S. 1955. Floral initiation, and fruit set in lychee, with special reference to the effect of sodium naphthaleneacetate. Bot. Gaz. 117:126-134. Nakata, S. 1956. Lychee flowering, and girdling. Hawaii Farm Sci. 4:4-5. Nakata, S., and R. Suehisa. 1969. Growth, and development of Litchi chinensis as affected by soil-moisture stress. Am. J. Bot. 56:1121-1126. Nakata, S., and Watanabe, Y. 1966. Effects of photoperiod, and night temperature on flowering of Litchi chinensis. Bot. Gaz. 127:146-152. Nixon, R. W. 1935. Metaxenia in dates. Proc. Amer. Soc. Hart. Sci. 32:221-226. Ochse, J. J., M. J. Jr. Soule, M. J. Dijkman, and C. Wehlburg. 1961. Tropical and subtropical agriculture, ValL Macmillian, New York. Olesen, T., C. M. Menzel, N. Wiltshire, and C. A. McConchie 1999. Manipulating flushing cycles, and flowering in lychee. Proc. 5th Natl. Lychee Conference, Twin Waters. Australia, p. 47-52. Oosthuizen, J. H. 1991. Lychee cultivation in South Africa. Austral. Lychee Yrbk. 1:51-55. Oppenheimer, C. 1947. The acclimatisation of new tropical, and subtropical fruit trees in Palestine. Agr. Res. Sta. Rehovot. Bul. 44. Pandey, V. S., and P. N. Bajpai. 1969. Studies on blossom bud differentiation in litchi var. 'Kalkattia,' and 'Rose Scented.' Indian J. Sci. Ind. 3:90-102. Pandey, R. M., and H. C. Sharma. 1989. The lychee. Indian Council of Agricultural Research, New Delhi. Pandey, R. S., and R. P. S. Yadava. 1970. Pollination of litchi (Litchi chinensis) by insects with special reference to honeybees. J. Apicult. Res. 9:103-105. Panhwar, F. 2000. Litchi cultivation in Sindh-Pakistan. 1st IntI. Symp. litchi, and longan. Guangzho, China, p. 19 (Abstr. A-O?). Paull, R. K, N. J. Chen, J. Deputy, H. Huang, G. Cheng, and F. Gao. 1984. Litchi growth, and compositional changes during fruit development. J. Am. Soc. Hart. Sci. 109:817-821. Penter, M., J. Kift, and P. J. C. Stassen. 2000. Chemical manipulation of litchi trees to improve fruit yield, and quality. Proc. 1st IntI. Symp. litchi, and longan. Guangzhou, China, p. 56 (Abstr. C-39). Phadke, K. G., and M. Nairn. 1974. Observation on the honeybee visitation to the Litchi (Nephelium litchi) blossoms at Pusa (Bihar India). Indian Bee J. 36:9-12. Pivovaro, S. Z. 1974. Studies of the floral biology, and the influence of growth regulators on fruit set, and drop of Litchi chinensis Sonn. (in Hebrew) MS Thesis, Hebrew Univ. Jerusalem, Israel. Popenoe, W. 1920. Manual of tropical, and subtropical fruits. p. 312-325. Macmillan, New York. Prasad, A., and O. S. Jauhari. 1963. Effect of 2,4,5-trichlorophenoxyacetic, and alpha naphthaleneacetic acids on "drop stop," and size of litchi fruits. Madras Agr. J. 50:28-29. Ramburn, N. 2001. Effect of girdling, and growth retardants on flowering, and fruiting of litchi trees in Mauritius. Acta Hort. 558:229-232. Reuveni, O. 1986. Date. p. 119-144. In: S. P. Monselise (ed.), Handbook offruit set, and development, CRC Press, Boca Raton, FL.
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
451
Robbertse, H., J. Fivas, and C. M. Menzel. 1995. A reevaluation of tree model, inflorescence morphology, and sex ratio in lychee (Litchi chinensis Sonn.). J. Am. Soc. Hort. Sci. 120:914-920. Robbertse, P. J., E. M. A. Steyn, and J. Fivaz. 1993. Pollination, and fruit set in Litchi chinensis Sonn. Yrbk. S. African Litchi Growers' Assoc. 5:12-14. Robbertse, P. J., E. M. A. Steyn, and A. J. Joubert. 1992. Ovule structure, pollen viability, and pollen tube growth in Litchi chinensis Sonn. cV HLH Mauritius. Yrbk. S. African Litchi Growers' Assoc. 4:5-7. Roe, D. J., J. H. Oosthuizen, and C. M. Menzel. 1995. Rate of soil drying, and previous water deficit influence the relationship between CO2 assimilation, and tree water status in potted lychee (Litchi chinensis Sonn.). J. Hort. Sci. 70:15-24. Samson, J. A. 1980. Tropical fruits. Longman Press, London. Scholefield, P. B. 1982. A scanning electron microscope study of flowers of avocado, litchi, macadamia, and mango. Scientia Hort. 16:263-272. Sedgley, M., and A. R. Griffin. 1989. Sexual reproduction of tree crops. Academic Press, London. Sedgley, M., P. B. Scholefield, and D. McE. Alexander. 1985. Inhibition of flowering of Mexican, and Guatemalan type avocados under tropical conditions. Scientia Hort. 25:21-30. Shalem-Galon, M. 1980. Lychee: fertilization, fruit set, and storage. (in Hebrew) MS Thesis, Hebrew Univ. Jerusalem, Israel. Shukla, R. K., and P. N. Bajpai. 1974. Blossom bud differentiation, and ontogeny in litchi (Litchi chinensis Sonn.). Indian J. Hort. 31:226-228. Singh, L. B., and U. P. Singh. 1954. The litchi. Lucknow: Superintendent, Printing, and Stationary, U.P. India. Singh, S., and B. S. Dhillon. 1981. Fruit drop pattern in litchi (Litchi chinensis Sonn.) cultivars, and its control by the use of auxins. Prog. Hort. 13:91-93. Singh, S. N. 1961. Studies on the morphology, and viability ofthe pollen grains of mango. Hort. Adv. 5:121-144. Singh, S. N. 1962. Studies on the morphology, and viability of the pollen grains of litchi. Hort. Adv. 6:28-52. Singh, U. S., and R. K. Lal. 1980. Influence of growth regulators on setting, retention, and weight of fruits in two cultivars of litchi. Scientia Hort. 12:321-326. Stern, R. A. 1992. Elucidation ofthe factors affecting litchi productivity in Israel, and the development of methods to improve its yield. PhD Diss., Faculty of Agr., Hebrew Univ. Jerusalem, Israel. Stern, R. A., I. Adato, M. Goren, D. Eisenstein, and S. Gazit. 1993a. Effect of autumnal water stress on litchi flowering, and yield in Israel. Scientia Hort. 54:295-302. Stern, R. A., D. Eisenstein, H. Voet, and S. Gazit. 1996b. Anatomical structure of two day old litchi ovules in relation to fruit set, and yield. J. Hort. Sci. 71:661-671. Stern, R. A., D. Eisenstein, H. Voet, and S. Gazit. 1997a. Female 'Mauritius' litchi flowers are not fully mature at anthesis. J. Hort. Sci. 72:19-25. Stern, R. A., and S. Gazit. 1993. Autumnal water stress checks vegetative growth, and increases flowering, and yield in litchi (Litchi chinensis Sonn.). Acta Hort. 349:209-212. Stern, R. A., and S. Gazit. 1996. Lychee pollination by the honeybee. J. Am. Soc. Hort. Sci. 121:152-157. Stern, R. A., and S. Gazit. 1997. Effect of 3,5,6-trichloro-2-pyridil-oxyacetic acid on fruit set, abscission, and yield of 'Mauritius' litchi. J. Hort. Sci. 72:659-663. Stern, R. A., and S. Gazit. 1998. Pollen viability in lychee. J. Am. Soc. Hort. Sci. 123:41-46. Stern, R. A., and S. Gazit. 1999. The synthetic auxin 3,5, 6-TPA reduces fruit drop, and increases yield in 'Kaimana' litchi. J. Hort. Sci. Biotech. 74:203-205.
452
R. STERN AND S. GAZIT
Stern, R. A., and S. Gazit. 2000a. Application of the polyamine putrescin increased yield of 'Mauritius' litchi (Litchi chinensis Sonn.) J. Hort. Sci. Biotech. 75:612-614. Stern, R. A., and S. Gazit. 2000b. Reducing fruit drop in lychee with PGR sprays. p. 211-222. In: A. Basra (ed.), Plant growth regulators in agriculture, and horticulture, Haworth Press Inc. New York. Stern, R. A., S. Gazit, R. El-Batsri, and C. Degani. 1993b. Pollen parent effect on outcrossing rate, yield, and fruit characteristics of 'Floridian', and 'Mauritius' lychee. J. Am. Soc. Hort. Sci. 118:109-114. Stern, R. A., S. Gazit, and M. Goren. 1996a. Factors affecting litchi productivity. (in Hebrew) Annu. Rep. for 1996. Ministry of Agr., Israel. Stern, R. A., S. Gazit, and M. Goren. 1997b. Factors affecting litchi productivity. (in Hebrew) Annu. Rep. for 1997. Ministry of Agr., Israel. Stern, R. A., J. Kigel, E. Tomer, and S. Gazit. 1995. Mauritius lychee fruit development, and reduced abscission after treatment with auxin 2,4,5-TP. J. Am. Soc. Hort. Sci. 120:65-70. Stern, R. A., M. Meron, A. Naor, R. Wallach, B. Bravdo, and S. Gazit. 1998. Effect of fall irrigation level in 'Mauritius', and 'Floridian' lychee on soil, and plant water status, flowering intensity, and yield. J. Am. Soc. Hort. Sci. 123:150-155. Stern, R. A., M. Nadler, and S. Gazit. 1997c. 'Floridian' litchi yield is increased by 2,4,5TP spray. J. Hort. Sci. 72:609-615. Stern, R. A., D. Stern, M. Harpaz, and S. Gazit. 2000. Applications of 2,4,5-TP, 3,5,6-TPA, and combinations thereof increases lychee fruit size, and yield. HortScience 35:661-664. Stern, R. A., D. Stern, H. Miller, X. Huafu, and S. Gazit. 2001. The effect of the synthetic auxin 2,4,5-TP, and 3,5,6-TPA on yield, and fruit size of young 'Fei Zi Xiao', and 'Hei Ye' litchi trees in Guangxi province, China. Acta Hort. 558:285-288. Stasser, R., and S. F. Anvari. 1982. On the senescence of ovules in cherries. Scientia Hort. 16:29-38. Subhadrabandhu, S. 1990. Lychee, and longan cultivation in Thailand. Rumthai Publ. Bangkok, Thailand. Subhadrabandhu, S., and A. Koo-Duang. 1987. Effect of ethephon on flowering of two lychee (Litchi chinensis Sonn.) cultivars. Acta Hort. 201:181-186. Subhadrabandhu, S., and C. Yapwattanaphun. 2001. Litchi, and longan production in Thailand. Acta Hort. 558:49-57. Tindall, H. D. 1994. Sapindaceous fruits: Botany, and horticulture. Hort. Rev. 16:143-196. Trung, H. M. 1999. Lychee production in Vietnam. Prospects, and problems. Proc. 5th Natl. Lychee Conference, Twin waters, Australia p. 83-87. Veera, S., and R. C. Das.1974. Effect of 2,4-D, NAA, GA, and 2,4,5-T on initial set, retention, and growth of fruits in litchi (Litchi chinensis Sonn.), var Muzaffarpur. Hort. Adv. 9:11-13. Verma, S. K., B. P. Jain., and S. R. Das. 1980. Preliminary studies on the evaluation of the effect of growth substances with minor elements in controlling fruit drop in litchi (Litchi chinensis Sonn.). Haryana J. Hort. Sci. 10:4-10. Wang, B., and Y. Qiu. 1997. Growth, and fruiting. p. 66-88. In: Z. W. Zhang, P. Y. Yuan, B. Q. Wang, Y. P. Qiu, andJ. S. Li. (eds.), Litchi, pictorial narration of cultivation. Pomology Research Institute, Guangdong Acad. Agr. Sci. Weaver, R. J. 1972. Plant growth substances in agriculture. Univ. California Press, Davis. Wu, D., X. Lin, Q. Ye, and W. Wang. 2001. Improvement offruit set in secondary panicle of 'Feizixiao' litchi by removal of the primary panicles. 1st IntI. Symp. litchi, and longan. Guangzho, China, p. 42 (Abstr. C-ll).
8. THE REPRODUCTIVE BIOLOGY OF THE LYCHEE
453
Xiang, X., 1. Ou, Y. Qiu, P. Yuan, and J. Chen. 2001. Embryo abortion, and pollen parent effects in Nuomici, and Guiwei litchi. Acta Hort. 558:257-260. Yee, W. 1972. The lychee in Hawaii. Univ. Hawaii, Coop. Ext. Servo Circ. 366. Young, T. H. 1970. Some climatic effects on flowering, and fruiting of Brewster lychees in Florida. Proc. Florida State Hart. Soc. 83:362-367. Young, T. W. 1977. Effect of branch girdling on yield of severely pruned Brewster lychee trees. Proc. Florida State. Hort. Soc. 90:251-253. Young, T. W., and R. W. Harkness. 1961. Flowering, and fruiting behavior of Brewster lychee in Florida. Proc. Florida State Hort. Soc. 74:358-363. Young, T. W., J. Popenoe, and C. W. Campbell. 1961. Physiological sprays on lychee. Annu. Rep. Florida Agr. Expt. Sta. p. 398-399. Yuan, R., and H. Huang. 1988. Litchi fruit abscission: its patterns, effect of shading, and relation to endogenous abscisic acid. Scientia Hart. 36:281-292. Yuan, R., and H. Huang. 1991. Effect ofNAA, NAA plus nucleotides on fruit set oflychee. Austral. Lychee Yrbk. 1:46-50. Zaragoza, S., 1. Trenor, E. Alonso, E. Primo-Millo, and M. Agusti. 1992. Treatment to increase the final fruit size of Satsuma Clausellina. Proc. IntI. Soc. Citricult. 2:725-728. Zee, F. T. P, H. T. Chan Jr., and C. R. Yen. 1998. Lychee, longan rambutan, and pulasan. p. 290-335. In: P. E. Shaw, H. T. Chan Jr., S. Nagy. (eds.), Tropical and subtropical fruits. Agscience Auburndale FL. Zhang, Z. W. 1997a. China, the native home of litchi, p. 12-17. In: Z. W. Zhang, P. Y. Yuan, B. Q. Wang, Y. P. Qiu, and J. S. LL (eds.), Litchi, pictorial narration of cultivation. Porno1ogy Res. Inst., Guangdong Acad. Agr. ScL, Guangzhou, China. Zhang, Z. W. 1997b. Cultivation practices for high yield. p. 106-139. In: Z. W. Zhang, P. Y. Yuan, B. Q. Wang, Y. P. Qiu, and J. S. Li. (eds.), Litchi, pictorial narration of cultivation. Pornology Res. Inst., Guangdong Acad. Agr. ScL, Guangzhou, China. Zhang, Z. W. 1997c. Main cultivars in Guangdong. p. 18-47. In: Z. W. Zhang, P. Y. Yuan, B. Q. Wang, Y. P. Qiu, and]. S. LL (eds.), Litchi, pictorial narration of cultivation. Pomology Res. Inst., Guangdong Acad. Agr. Sci., Guangzhou, China. Zheng, Q. T., L. Davenport, and Y. LL 2001. Stem age, winter temperature, and flowering of lychee in South Florida. Acta Hort. 558:237-240.
Subject Index (Volume 28) A
Abscission, lychee, 437-443 Allium phytonutrients, 156-159 B
Brassica classification, 27-28
c Cactus grafting, 106-109 Classification, 1-6 Brassica, 27-28 lettuce, 25-27 potato, 23-26 tomato, 21-23 Crucifers phytochemicals, 150-156 Cucumber grafting, 91-96
phytochemicals, 125-185 volatiles, pear, 237-324 Fruit crops: lychee, 393-453 peach thinning, 351-392 pear volatiles, 237-324 virus elimination, 187-236 G
Genetics and breeding, grafting use, 109-115 Graft and grafting, herbacious, 61-124
H Health phytochemicals, vegetables, 125-185 L
D
Dedication, Stevens, M.A., xi-xiii E
Eggplant grafting, 103-104 Eggplant phytochemicals, 162-163 F Flower and flowering: Lychee,397-421 strawberry, 325-349 Fruit: lychee, 433-444 pear volatiles, 237-324
Lettuce classification, 25-27 Lychee: fruit abscission, 437-443 reproductive biology, 393-453 flowering, 397-421 fruit development, 433-436 pollination, 422-428 M
Melon grafting, 96-98 N
Nomenclature, 1-60 Taxonomy, 1-60
Horticultural Reviews, Volume 28, Edited by Jules Janick ISBN 0-471-21542-2 © 2003 John Wiley & Sons, Inc. 454
455
SUBJECT INDEX
o
T
Ornamental plants, cactus grafting, 106-109
p Peach thinning, 351-392 Pear, fruit volatiles, 237-324 Pepper: grafting, 104-105 phytochemicals, 161-162 Physiology: grafting, 78-84 lychee reproduction, 393--453 strawberry flowering, 325-349 Plant: classification, 1-60 systematics, 1-60 Pollination, lychee, 422-428 Potato: classification, 23-26 phytochemicals, 160-161
s Strawberry, flowering, 325-349 Systematics, 1-60
Thinning, peach and Prunus, 351-392 Tomato: classification, 21-23 grafting, 98-103 phytochemicals, 160
v Vegetable crops: Allium phytochemicals, 156-159 cucumber grafting, 91-96 crucifer phytochemicals, 150-156 eggplant grafting, 103-104 eggplant phytochemicals, 162-163 grafting, 61-124 melon grafting 96-98 pepper phytochemicals, 161-162 potato phytochemicals, 160-161 tomato phytochemicals, 160 phytochemicals, 125-185 watermelon grafting, 86-91 Virus elimination, 187-236 Volatiles, pear, 237-324
w Watermelon grafting, 86-91
455
Cumulative Subject Index (Volumes 1-28)
A
Abscisic acid: chilling injury, 15:78-79 cold hardiness, 11 :65 dormancy, 7:275-277 genetic regulation, 16:9-14, 20-21 lychee, 28:437-443 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 Agapanthus, 25:56-57 Agaricus, 6:85-118 Agrobacterium tumefaciens, 3:34 Air pollution, 8:1-42 Alkaloids, steroidal, 25:171-196 Allium phytonutrients, 28:156-159 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 bearinu' chemical thin~ing, 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 Amarcrinum, 25: 57 Amaryllidaceae, growth, development, flowering, 25:1-70 Amaryllis, 25:4-15 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 orchid,5:281-283 navel orange, 8:132-133
Horticultural Reviews, Volume 28, Edited by Jules Janick ISBN 0-471-21542-2 © 2003 John Wiley & Sons, Inc. 456
457
CUMULATIVE SUBJECT INDEX
pecan flower, 8:217-255 petal senescence, 1:212-216 pollution injury, 8:15 waxes, 23:1-68 Androgenesis, woody species, 10:171-173
Angiosperms, embryogenesis, 1:1-78 Anthurium: see also Aroids, ornamental fertilization, 5:334-335 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--4 74 flavor, 16:197-234 flower induction, 4:174-203 fruiting, 11:229-287 fruit cracking and splitting, 19:217-262
functional phytonutrients, 27:304 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 scald, 27:227-267 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 weight loss, 25:197-234 yield, 1:397--424 Apricot: bloom delay, 15:101-102 CA storage, 1:309 origin and dissemination, 22:225-266
Arabidopsis: molecular biology of flowering, 27:1-39,41-77
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; 24:6-7; 26:105-110
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: CA and MA, 22:135-141 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
CUMULATIVE SUBJECT INDEX
458
Bacteriophage, fire blight control, 1:449-450
Banana: CA and MA, 22:141-146 CA storage, 1:311-312 fertilization, 1:105 in vitro culture, 7:178-180 Banksia, 22:1-25 Bean: CA storage, 1:352-353 fluid drilling of seed, 3 :21 resistance to bacterial pathogens, 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 Biennial bearing. See Alternate bearing Biochemistry, petal senescence, 11:15-43 Bioreactor technology, 24:1-30 Bioregulation: See also 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 Brassica classification, 28:27-28 Brassicaceae, in vitro, 5:232-235 Breeding. See Genetics and breeding Broccoli, CA storage, 1:354-355 Brussels sprouts, CA storage, 1:355
Bulb crops: See also Tulip development, 25:1-70 flowering, 25:1-70 genetics and breeding, 18:119-123 growth, 25: 1-70 in vitro, 18:87-169 micropropagation, 18:89-113 root physiology, 14:57-88 virus elimination, 18:113-123
c CA storage. See Controlled-atmosphere storage Cabbage: CA storage, 1:355-359 fertilization, 1:117-118 Cactus: crops, 18:291-320 grafting, 28:106-109 reproductive biology, 18:321-346 Caladium. See Aroids, ornamental Calciole, nutrition, 10:183-227 Calcifuge, 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 Caparis, See Caper bush Caper bush, 27:125-188 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
Carbon dioxide, enrichment, 7:345-398, 544-545
Carnation, fertilization, 1:100; 5:341-345
CUMULATIVE SUBJECT INDEX
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; 26:85-159 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 Cherimoya, CA and MA, 22:146-147 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 injury, chlorophyll fluorescence, 23:79-84 pistachio, 3:388-389 Chlorine: deficiency and toxicity symptoms in fruits and nuts, 2:153 nutrition, 5:239 Chlorophyll fluorescence, 23:69-107 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
459 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 functional phytochemicals, fruit, 27:269-315 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 practices for young trees, 24:319-372 rootstock, 1:237-269 viroid dwarfing, 24:277-317 Classification:
Brassica, 28:27-28 lettuce, 28:25-27 potato, 28:23-26 tomato, 28:21-23 Clivia, 25:57 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 Co10casia, 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-atmosphere (CA) storage: asparagus, 12:76-77, 127-130 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 tropical fruit, 22:123-183 tulip, 5:105
CUMULATIVE SUBJECT INDEX
460 Controlled-atmosphere (CA) storage (cont.) vegetable quality, 8:101-127 vegetables, 1:337-394; 4:259-260 Controlled environment agriculture, 7:534-545, see also Greenhouse and greenhouse crops; hydroponic culture; protected culture 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 Crinum, 25:58 Crucifers phytochemicals, 28:150-156 Cryopreservation: apical meristems, 6:357-372 cold hardiness, 11:65-66 Cryphonectria parasitica. See Endothia parasitica Crytosperma, 8:47, 58, see also Aroids Cucumber: CA storage, 1:367-368 grafting, 28:91-96 Cucurbita pepo, cultivar groups history, 25:71-170 Currant, harvesting, 16:311-327 Custard apple, CA and MA, 22:164 Cyrtanthus, 25:15-19 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., 1: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 Dennis, F.G., 22:xi-xii De Hertogh, A.A., 26:xi-xii Faust, Miklos, 5:vi-x Hackett, W.P., 12:x-xiii Halevy, A.H., 8:x-xii Hess, c.E., 13:x-xii Kader, A.A., 16:xii-xv Kamemoto, H., 24:x-xiii Looney, N.E., 18:xiii Magness, J.R., 2:vi-viii Moore, J.N., 14:xii-xv Possingham, J.V., 27:xi-xiii Pratt, c., 20:ix-xi Proebsting, Jr., E.L., 9:x-xiv Rick, Jr., C.M., 4:vi-ix Ryugo, K., 25:x-xii Sansavini, S., 17:xii-xiv Sherman, W.B., 21:xi-xiii Smock, RM., 7:x-xiii Stevens, M.A., 28:xi-xiii Weiser, c.J., l1:x-xiii Whitaker, T.W., 3:vi-x Wittwer, S.H., 10:x-xiii Yang, S.F., 23:xi 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
CUMULATIVE SUBJECT INDEX cassava, 12:163-164 control by virus, 3:399-403 controlled-atmosphere storage,
461
Environment: air pollution, 8:20-22 controlled for agriculture, 7:534-545
3:412-461
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 waxes, 23:1-68 yam (Dioscorea), 12:181-183 Disorder: see also 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 Durian, CA and MA, 22:147-148 Dwarfing: apple, 3:315-375 apple mutants, 12:297-298 by virus, 3:404-405
controlled for energy efficiency, 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 Eriobotrya japonica. See Loquat 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
E
Easter lily, fertilization, 5:352-355 Eggplant: grafting, 28:103-104 phytochemicals, 28:162-163 Embryogenesis. See Asexual embryogenesis Endothia parasitica, 8:291-336 Energy efficiency, in greenhouses, 1:141-171; 9:1-52
kiwifruit respiration, 6:47-48 mechanical stress, 17:16-17 petal senescence, 11:16-19, 27-30 rose senescence, 9:65-66 Eucharis, 25:19-22 Eucrosia, 25:58 F
Feed crops, cactus, 18:298-300 Feijoa, CA and MA, 22:148
462 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 zinc nutrition, 23:109-128 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 Floral scents, 24:31-53 Floricultural crops: see also individual crops: Amaryllidaceae, 25:1-70 Banksia, 22:1-25 fertilization, 1:98-104 growth regulation, 7:399-481 heliconia, 14:1-55
Leucospermum, 22:27-90 postharvest physiology and senescence, 1:204-236; 3:59-143; 10:35-62; 11:15-43 Pratea, 26:1-48 Florigen, 4:94-98 Flower and flowering: Amaryllidaceae, 25:1-70 apple anatomy and morphology, 10:277-283
CUMULATIVE SUBJECT INDEX
apple bioregulation, 10:344-348 Arabidopsis, 27:1-39, 41-77 aroids, ornamental, 10:19-24 avocado, 8:257-289 Banksia, 22:1-25 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 homeotic gene regulation, 27:41-77 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
Leucospermum, 22:27-90 lychee, 28:397-421 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 protea 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 scents, 24:31-53 senescence, 1:204-236; 3:59-143; 10:35-62; 11:15-43; 18:1-85 strawberry, 28:325-349 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
463
CUMULATIVE SUBJECT INDEX
fertilization, 1:102-103; 5:367-380 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 abscission, 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 apple scald, 27:227-267 apple weight loss, 25:197-234 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 coating physiology, 26:161-238 cracking, 19:217-262 diseases in CA storage, 3:412-461 drop, apple functional phytochemicals, 27:269-315 growth measurement, 24:373-431 kiwifruit, 6:35-48; 12:316-318 loquat, 23:233-276 lychee, 28:433-444 maturity indices, 13:407-432 navel orange, 8:129-179 nectarine, postharvest, 11:413-452 nondestructive postharvest quality evaluation, 20:1-119 olive processing, 25:235-260 peach, postharvest, 11:413-452 pear, bioregulation, 10:348-374 pear, fruit disorders, 11:357-411 pear maturity indices, 13:407-432 pear ripening and quality, 10:361-374 pear scald, 27:227-267 pear volatiles, 28:237-324 pistachio, 3:382-391 phytochemicals, 28:125-185
plum, 23:179-231 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 volatiles, pear, 28:237-324 Fruit crops: see also individual crop 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 apple scald, 27:227-267 apricot, origin and dissemination, 22:225-266
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 and MA for tropicals, 22:123-183 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, culture of young trees, 24:319-372
citrus dwarfing by viroids, 24:277-317 citrus flowering, 12:349-408 cranberry, 21:215-249
464
CUMULATIVE SUBJECT INDEX
Fruit crops (cant.) 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 irrigation, 27:189-225 grape nitrogen metabolism,
pecan flowering, 8:217-255 photosynthesis, 11 :111-15 7 Phytophthora control, 17:299-330 plum origin, 23:179-231 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 virus elimination, 28:187-236 water status, 7:301-344 Functional phytochemicals, fruit,
14:407-452
grape pnming, 16:235-254, 336-340 grape root, 5:127-168 grape seedlessness, 11 :164-176 grapevine pruning, 16:235-254, 336-340
27:269-315
Fungi: fig, 12:451-474 mushroom, 6:85-118 mycorrhiza, 3:172-213; 10:211-212 pathogens in postharvest storage,
honey bee pollination, 9:244-250, 254-256 jojoba, 17:233-266 in vitro culture, 7:157-200; 9:273-349 irrigation, deficit, 21:105-131 kiwifruit, 6:1-64; 12:307-347 lingonberry, 27:79-123 longan, 16:143-196 loquat, 23:233-276 lychee, 16:143-196, 28:393-453 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 peach thinning, 28:351-392 pear fruit disorders, 11:357-411; 27:227-267
pear maturity indices, 13:407-432 pear scald, 27:227-267 pear volatiles, 28:237-324
3:412-461
truffle cultivation, 16:71-107 Fungicide, and apple fruit set, 1:416 G
Galanthus, 25:22-25 Garlic, CA storage, 1:375 Genetic variation: alternate bearing, 4:146-150 photoperiodic response, 4:82 pollution injury, 8:16-19 ternperature-photoperiod interaction, 17:73-123
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
CUMULATIVE SUBJECT INDEX flowering, 15:287-290, 303-305, 306-309,314-315;27:1-39,41-77 flower longevity, 1:208-209 ginseng, 9:197-198 grafting use, 28:109-115 in vitro techniques, 9:318-324; 18:119-123 lettuce, 2:185-187 lingonberry, 27:108-111 loquat, 23:252-257 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 waxes, 23:50-53 woody legume tissue and cell culture, 14:311-314 yam (Dioscorea), 12:183 Geophyte. See Bulb, tuber Geranium, fertilization, 5:355-357 Germination, seed, 2:117-141, 173-174; 24:229-275 Germplasm: cryopreservation,6:357-372 in vitro, 5:261-264; 9:324-325 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
465 Glucosinolates, 19:99-215 Gourd, history, 25:71-171 Graft and grafting: herbaceous, 28:61-124 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 functional phytochemicals, 27:291-298 irrigation, 27:189-225 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; 24:55-138, see also Abscisic acid, Auxin, Cytokinins, Ethylene, Gibberellins 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, 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
CUMULATIVE SUBJECT INDEX
466
Growth substances (cont.) 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 hormone reception, 26:49-84 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
Haemanthus, 25:25-28 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 Health phytochemicals: fruit, 27:269-315 vegetables, 28:125-185 Heat treatment (postharvest), 22:91-121 Heliconia, 14:1-55 Herbaceous plants, subzero stress, 6:373-417
Hippeastrum, 25:29-34 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 HymenocaJJis, 25:59 Hypovirulence, in Endothia parasitica, 8:299-310
Ismene, 25:59 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, 2:52 tulip, 5:63, 92 waxes, 23:1-68 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 bioreactor technology, 24:1-30 bulbs, flowering, 18:87-169 cassava propagation, 13:121-123; 26:99-119
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 bulbs, 18:87-169 flowering, 4:106-127 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
467
CUMULATIVE SUBJECT INDEX thin cell layer morphogenesis, 14:239-264 woody legume culture, 14:265-332 Iron: deficiency and toxicity symptoms in fruits and nuts, 2:150 deficiency chlorosis, 9:133-186 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, 27:189-225 grape root growth, 5:140-141 lettuce industry, 2:175 navel orange, 8:161-162 root growth, 2:464-465
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 Lanzon, CA and MA, 22:149 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 classification, 28:25-27 fertilization, 1:118 fluid drilling of seed, 3:14-17 industry, 2:164-207 seed germination, 24:229-275 tipburn, 4:49-65 Leucojum, 25:34-39 Leucospermum, 22:27-90 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 Lingonberry, 27:79-123 Longan: See also Sapindaceous fruits CA and MA, 22:150 Loquat: botany and horticulture, 23:233-276 CA and MA, 22:149-150 Lychee: See also Sapindaceous fruits CA and MA, 22:150 flowering, 28:397-421 fruit abscission, 28-437-443 fruit development, 28:433-436 pollination, 28:422-428 reproductive biology, 28:393-453 Lycoris, 25:39-43 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
CUMULATIVE SUBJECT INDEX
468 Magnetic resonance imaging, 20:78-86, 225-266 Male sterility, temperature-photoperiod 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 and MA, 22:151-157 CA storage, 1:313 in vitro culture, 7:171-173 Mangosteen, CA and MA, 22:157 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 Melon grafting, 28:96-98 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 also In vitro; propagation: bulbs, flowering, 18:89-113 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 Modified atmosphere (MA) for tropical fruits, 22:123-183 Moisture, and seed storage, 2:125-132
Molecular biology: cassava, 26:85-159 floral induction, 27:3-20 flowering, 27:1-39;41-77 hormone reception, 26:49-84 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
Narcissus, 25:43-48 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 Nerine, 25:48-56 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 Ericaceae nutrition, 10:198-202 fixation in woody legumes, 14:322-323
CUMULATIVE SUBJECT INDEX foliar application, 6:332 in embryogenesis, 2:273-275 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 vegetable crops, 22:185-223 Nomenclature, 28:1-60 Nondestructive quality evaluation of fruits and vegetables, 20:1-119 Nursery crops: fertilization, 1:106-112 nutrition, 9:75-101 Nut crops: see also individual crop 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 phytochemicals in fruit, 27:269-315 phytochemicals in vegetables, 28:125-185
steroidal alkaloids, 25:171-196 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
469
ecologically based, 24:156-172 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 nitrogen in vegetable crops, 22:185-223
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 processing technology, 25:235-260 Onion: CA storage, 1:373-375 fluid drilling of seed, 3:17-18 Opium poppy, 19:373-408 Orange: see also 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
CUMULATIVE SUBJECT INDEX
470 Orchid (cont.) pollination regulation of flower development, 19:28-38 physiology, 5:279-315 Organogenesis, 3:214-314, see also In vitro; tissue culture Ornamental plants: see also individual plant Amaryllidaceae Banksia, 22:1-25 cactus grafting, 28-106-109 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 Leucospermum, 22:27-90 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 and MA, 22:157-160 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 Passion fruit: in vitro culture, 7:180-181 CA and MA, 22:160-161 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 thinning, 28:351-392 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, 11:357-411; 27:227-267 fruit volatiles, 28:237-324 in vitro, 9:321 maturity indices, 13:407-432 root distribution, 2:456 scald, 27:227-267 short life, 2:6 Pecan: alternate bearing, 4:139-140 fertilization, 1:106 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 grafting, 28:104-105 phytochemicals, 28:161-162 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 ecologically based, 24:172-201 fig, 12:442-477 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
CUMULATIVE SUBJECT INDEX
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 also 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 floral scents, 24:31-53 flower development, 19:1-58 flowering, 4:106-127 fruit ripening, 13:67-103 fruit softening, 10:107-152 ginseng, 9:211-213
471 glucosinolates, 19:99-215 grafting, 28:78-84 heliconia, 14:5-13 hormone reception, 26:49-84 juvenility, 7:109-155 lettuce seed germination, 24:229-275 light tolerance, 18:215-246 loquat, 23:242-252 lychee reproduction, 28:393-453 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 strawberry flowering, 28:28:325-349 subzero stress, 6:373-417 summer pruning, 9:351-375 sweet potato, 23:277-338 thin cell layer morphogenesis, 14:239-264 tomato fruit ripening, 13:67-103 tomato parthenocarpy, 6:71-74 triazoles, 10:63-105; 24:55-138 tulip, 5:45-125 vernalization, 17:73-123 volatiles, 17:43-72 watercore, 6:189-251 water relations cut flowers, 18:1-85 waxes, 23:1-68 Phytochemicals, functional: fruits, 27:269-315 vegetables, 28:125-185
472
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 and MA, 22:161-162 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: CA and MA, 22:141-146 in vitro culture, 7:178-180 Plant: classification, 28: 1-60 protection, short life, 2:79-84 systematics, 28:1-60 Plastic cover, sad production, 27:317-351 Plum: CA storage, 1:309 origin, 23:179-231 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 floral scents, 24:31-53 flower regulation, 19:1-58 fruit crops, 12:223-264 fruit set, 4:153-154 ginseng, 9:201-202 grape, 13:331-332 heliconia, 14:13-15 honey bee, 9:237-272 kiwifruit, 6:32-35 lychee, 28:422-428 navel orange, 8:145-146
CUMULATIVE SUBJECT INDEX 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 Poppy, opium, 19:373-408 Postharvest physiology: almond, 20:267-311 apple bitter pit, 11 :289-355 apple maturity indices, 13:407-432 apple scald, 27:227-257 apple weight loss, 25:197-234 aroids, 8:84-86 asparagus, 12:69-155 CA for tropical fruit, 22:123-183 CA storage and quality, 8:101-127 chlorophyll fluorescence, 23:69-107 coated fruits & vegetables, 26:161-238 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 heat treatment, 22:91-121 lettuce, 2:181-185 low-temperature sweetening, 17:203-231 MA for tropical fruit, 22:123-183 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; 27:227-267 pear maturity indices, 13:407-432 pear scald, 27:227-257 petal senescence, 11:15-43 protea leaf blackening, 17:173-201 quality evaluation, 20:1-119 scald, 27:227-267 seed,2:117-141 texture in fresh fruit, 20:121-244 tomato fruit ripening, 13:67-103 vegetables, 1:337-394
473
CUMULATIVE SUBJECT INDEX 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 classification, 28:23-26 fertilization, 1:120-121 low temperature sweetening, 17:203-231 phytochemicals, 28:160-161 tuberization, 14:89-198 Processing, table olives, 25:235-260 Propagation: see also In vitro apple, 10:324-326; 12:288-295 aroids, ornamental, 10:12-13 bioreactor technology, 24:1-30 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 Protaceous flower crop: see also Protea Banksia, 22:1-25
Leucospermum, 22:27-90 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 also Almond; Cherry; Nectarine; Peach; Plum in vitro, 5:243-244; 9:322 root distribution, 2:456
Pseudomonas: phaseo1icola, 3:32-33, 39,44-45 solanacearum, 3:33 syringae, 3:33, 40; 7:210-212 Pumpkin, history, 25:71-170 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 CA and MA, 22:163 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
CUMULATIVE SUBJECT INDEX
474
Root (cant.) 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: Amaryllidaceae, 25:1-79 aroids, 8:43-99; 12:166-170 cassava, 12:158-166; 26:85-159 low-temperature sweetening, 17:203-231
minor crops, 12:184-188 potato tuberization, 14:89-188 sweet potato, 12:170-176 sweet potato physiology, 23:277-338 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 Sapodilla, CA and MA, 22:164 Scadoxus, 25:25-28
Scald, apple and pear, 27:227-265 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 lettuce germination, 24:229-275 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: chlorophyll senescence, 23:88-93 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 Signal transduction, 26:49-84 Small fruit, CA storage, 1:308 Snapdragon fertilization, 5:363-364 Sod production, 27:317-351 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 plant relations, trickle irrigation, 4:18-21
stress, 4:151-152 testing, 7:1-68; 9:88-90 zinc, 23:109-178 Soilless culture, 5:1-44
475
CUMULATIVE SUBJECT INDEX Solanaceae: in vitro, 5:229-232 steroidal alkaloids, 25:171-196 Somatic embryogenesis. See Asexual embryogenesis Sorghum, sweet, 21:73-104 Spathiphyllum. See Aroids, ornamental Squash, history, 25:71-170 Stem, apple morphology, 12:272-283 Sternbergia, 25:59 Steroidal alkaloids, solanaceous, 25:171-196 Storage: see also 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 flowering, 28:325-349 fruit growth and ripening, 17:267-297 functional phytonutrients, 27: 303-304 harvesting, 16:348-365 in vitro, 5:239-241 Stress: benefits of, 4:247-271 chlorophyll fluorescence, 23:69-107 climatic,4:150-151 flooding, 13:257-313 mechanical, 17:1-42 petal, 11:32-33 plant, 2:34-37 protectants (triazoles), 24:55-138 protection, 7:463-466 salinity tolerance in olive, 21:177-214 subzero temperature, 6:373-417 waxes, 23:1-68 Sugar: see also Carbohydrate allocation, 7:74-94 flowering, 4:114 Sugar apple, CA and MA, 22:164 Sugar beet, fluid drilling of seed, 3:18-19 Sulfur: deficiency and toxicity symptoms in fruits and nuts, 2:154 nutrition, 5:323-324 Sweet potato: culture, 12:170-176
fertilization, 1:121 physiology, 23:277-338 Sweet sop, CA and MA, 22:164 Symptoms, deficiency and toxicity symptoms in fruits and nuts, 2:145-154 Syngonium. See Aroids, ornamental Systematics, 28:1-60 T Taro. See Aroids, edible Taxonomy, 28:1-60 Tea, botany and horticulture, 22:267-295 Temperature: apple fruit set, 1:408-411 bloom delay, 15:119-128 CA storage of vegetables, 1:340-341 chilling injury, 15:67-74 cryopreservation, 6:357-372 cut flower storage, 10:40-43 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 peach and Prunus, 28:351-392 Tipburn, in lettuce, 4:49-65 Tissue: see also 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, 24:1-30 cassava, 26:85-159 dwarfing, 3:347-348 nutrient analysis, 7:52-56; 9:90
476 Tomato: CA storage, 1:380-386 classification, 28:21-23 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 grafting,28:98-103 greenhouse quality, 26:239 parthenocarpy, 6:65-84 phytochemicals, 28:160 Toxicity symptoms in fruit and nut crops, 2:145-154 Transport, cut flowers, 3:100-104 Tree decline, 2:1-116 Triazoles, 10:63-105; 24:55-138 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 also Bulb 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; Lingonberry functional phytonutrients, 27:303 Vase solutions, 3:82-95; 10:46-51 Vegetable crops: see also Specific crop Allium phytochemicals, 28:156-159 aroids, 8:43-99; 12:166-170 asparagus postharvest, 12:69-155 cactus, 18:300-302
CUMULATIVE SUBJECT INDEX cassava, 12:158-166; 13:105-129; 26:85-159 CA storage, 1:337-394 CA storage and quality, 8:101-127 CA storage diseases, 3:412-461 Caper bush, 27:125-188 chilling injury, 15:63-95 coating physiology, 26:161-238 crucifer phytochemicals, 28:150-156 cucumber grafting, 28:91-96 ecologically based, 24:139-228 eggplant grafting, 28:103-104 eggplant phytochemicals, 28:162-163 fertilization, 1:117-124 fluid drilling of seeds, 3:1-58 gourd history, 25:71-170 grafting, 28:61-124 greenhouse management, 21:1-39 greenhouse pest management, 13:1-66 honey bee pollination, 9:251-254 hydroponics, 7:483-558 lettuce seed germination, 24:229-275 low-temperature sweetening, 17:203-231 melon grafting, 28:96-98 minor root and tubers, 12:184-188 mushroom cultivation, 19:59-97 mushroom spawn, 6:85-118 N nutrition, 22:185-223 nondestructive postharvest quality evaluation, 20:1-119 okra, 21:41-72 pepper phytochemicals, 28:161-162 phytochemicals, 28:125-185 potato phytochemicals, 28:160-161 potato tuberization, 14:89-188 pumpkin history, 25:71-170 seed conditioing, 13:131-181 seed priming, 16:109-141 squash history, 25:71-170 steroidal alkaloids, Solanaceae, 25:171-196 sweet potato, 12:170-176 sweet potato physiology, 23:277-338 tomato fruit ripening, 13:67-103 tomato (greenhouse) quality: 26:239-319 tomato parthenocarpy, 6:65-84
477
CUMULATIVE SUBJECT INDEX tomato phytochemicals, 28:160 tropical production, 24:139-228 truffle cultivation, 16:71-107 watermelon grafting, 28:86-91 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 also Cowpea genetics, 2:311-394 U.S. production, 12:197-222 Viroid, dwarfing for citrus, 24:277-317 Virus: benefits in horticulture, 3:394-411 dwarfing for citrus, 24:277-317 elimination, 7:157-200; 9:318; 18:113-123; 28:187-236 fig, 12:474-475 tree short life, 2:50-51 turnip mosaic, 14:199-238 Volatiles, 17:43-72; 24:31-53; 28:237-324 Vole, 6:254-274
w 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, grape and grapevine, 27:189-225 kiwifruit, 12:332-339 light in orchards, 2:248-249 photosynthesis, 11:124-131 trickle irrigation, 4:1-48 Watercore, 6:189-251 apple, 6:189-251 pear, 11:385-387
Watermelon: fertilization, 1:124 grafting, 28:86-91 Wax apple, CA and MA, 22:164 Waxes, 23:1-68 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
x Xanthomonas phaseoli, 3:29-32, 41, 45-46 Xanthophyll cycle, 18:226-239 Xanthosoma, 8:45-46, 56-57, see also Aroids Sugar: see also Carbohydrate allocation, 7:74-94 flowering, 4:114 y Yam (Dioscorea), 12:177-184 Yield: determinants, 7:70-74; 97-99 limiting factors, 15:413-452
z Zantedeschia. See Aroids, ornamental Zephyranthes,25:60-61 Zinc: deficiency and toxicity symptoms in fruits and nuts, 2:151 foliar application, 6:332, 336 nutrition, 5:326; 23:109-178 pine bark media, 9:124
Cumulative Contributor Index (Volumes 1-28)
Abbott, J.A., 20:1 Adams III, W.W., 18:215 Aldwinckle, H.S., 1:423; 15:xiii Amarante, e., 28:161 Anderson, I.e., 21:73 Anderson, J.L., 15:97 Anderson, P.e., 13:257 Andrews, P.K., 15:183 Ashworth, E.N., 13:215; 23:1 Asokan, M.P., 8:43 Atkinson, D., 2:424 Aung, L.H., 5:45
Bower, J.P., 10:229 Bradley, G.A., 14:xiii Brandenburg, W., 28:1 Brennan, R, 16:255 Broadbent, P., 24:277 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, RE., 6:253; 28:351
Bailey, W.G., 9:187 Baird, L.A.M., 1:172 Banks, N.H., 19:217; 25:197; 26:161 Barden, J.A., 9:351 Barker, A.V., 2:411 Bass, L.N., 2:117 Bassett, e. L., 26:49 Becker, J.S., 18:247 Beer, S.V., 1:423 Behboudian, M.H., 21:105; 27:189 Bennett, AB., 13:67 Benschop, M., 5:45 Ben-Ya'acov, A., 17:381 Benzioni, A, 17:233 Bevington, K.B., 24:277 Bewley, J.D., 18:171 Binzel, M.L., 16:33 Blanpied, G.D., 7:xi Bliss, F.A, 16:xiii; 28:xi Boardman, K. 27 xi Borochov, A, 11:15
Caldas, L.S., 2:568 Campbell, L.E., 2:524 Cantliffe, D.J., 16:109; 17:43; 24:229; 28:325 Carter, G., 20:121 Carter, J.V., 3:144 Cathey, H.M., 2:524 Chambers, RJ., 13:1 Chandler, e.K. 28:325 Charron, e.S., 17:43 Chen, Z., 25:171 Chin, e.K., 5:221 Clarke, N.D., 21:1 Coetzee, J. H., 26:1 Cohen, M., 3:394 Collier, G.F., 4:49 Collins, G., 25:235 Collins, W.L., 7:483 Colmagro, S., 25:235 Compton, M.E., 14:239 Conover, e.A., 5:317; 6:119
Horticultural Reviews, Volume 28, Edited by Jules Janick ISBN 0-471-21542-2 © 2003 John Wiley & Sons, Inc. 478
479
CUMULATIVE CONTRIBUTOR INDEX Coppens d'Eeckenbrugge, G., 21:133 Costa, G. 28:351 Coyne, D.P., 3:28 Crane, J.e., 3:376 Criley, RA., 14:1; 22:27; 24:x Crawly, W., 15:1 Cutting, J.G., 10:229 Daie, J., 7:69 Dale, A., 11:185; 16:255 Darnell, RL., 13:339, 28:325 Davenport, T.L., 8:257; 12:349 Davies, F.S., 8:129; 24:319 Davies, P.J., 15:335 Davis, T.D., 10:63; 24:55 Decker, H.F., 27:317 DeEll, J.R, 23:69 DeGrandi-Hoffman, G., 9:237 De Hertogh, A.A., 5:45; 14:57; 18:87; 25:1 Deikman, J., 16:1 DellaPenna, D., 13:67 Demmig-Adams, B., 18:215 Dennis, F.G., Jr., 1:395 Dorais, M., 26:239 Doud, S.L., 2:1 Dudareva, N., 24:31 Duke, S.O., 15:371 Dunavent, M.G., 9:103 Duval, M.-F., 21:133 Diizyaman, E., 21:41 Dyer, W.E., 15:371 Early, J.D., 13:339 Eastman, K., 28:125 Elfving, D.e., 4:1; 11:229 EI-Goorani, M.A., 3:412 Esan, E.B., 1:1 Evans, D.A., 3:214 Ewing, E.E., 14:89 Faust, M., 2:vii, 142; 4:174; 6:287; 14:333; 17:331; 19:263; 22:225; 23:179 Fenner, M., 13:183 Fenwick, G.R, 19:99 Ferguson, A.R, 6:1 Ferguson, I.B., 11:289 Ferguson, J.J., 24:277 Ferguson, L., 12:409 Ferree, D.e., 6:155 Ferreira, J.F.S., 19:319
Fery, RL., 2:311; 12:157 Fischer, RL., 13:67 Fletcher, RA., 24:53 Flick, e.E., 3:214 Flore, J.A., 11:111 Forshey, e.G., 11:229 Franks, R G., 27:41 Fujiwara, K., 17:125 Gazit, S., 28:393 Geisler, D., 6:155 Geneve, RL., 14:265 George, W.L., Jr., 6:25 Gerrath, J.M., 13:315 Gilley, A., 24:55 Giovannetti, G., 16:71 Giovannoni, J.J., 13:67 Glenn, G.M., 10:107 Goffinet, M.e., 20:ix Goldschmidt, E.E., 4:128 Goldy, RG., 14:357 Goren, R, 15:145 Gosselin, A., 26:239 Goszczynska, D.M., 10:35 Grace, S.e., 18:215 Graves, CJ., 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.I., 17:299 Guiltinan, M.J., 16:1 Hackett, W.P., 7:109 Halevy, A.H., 1:204; 3:59 Hallett, I.C, 20:121 Hammerschmidt, R, 18:247 Hanson, E.J., 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 Hetterscheid, W.L.A., 28:1 Heywood, V., 15:1 Hjalmarsson, I., 27:79-123
480 Hogue, E.]., 9:377 Holt, J.S., 15:371 Huber, D.J., 5:169 Hunter, E.1., 21:73 Hutchinson, J.F., 9:273 Hutton, RJ., 24:277 Indira, P., 23:277 Ingle, M. 27:227 Isenberg, F.M.R, 1:337 Iwakiri, B.T., 3:376 Jackson, J.E., 2:208 Janick, J., 1:ix; 8:xi; 17:xiii; 19:319; 21:xi; 23:233 Jarvis, W.R, 21:1 Jenks, M.A., 23:1 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 Kalt, W. 27:269; 28:125 Kang, S.-M., 4:204 Kato, T., 8:181 Kawa, L., 14:57 Kawada, K., 4:247 Kelly, J.F., 10:ix; 22:xi Kester, D.E., 25:xii Khan, A.A., 13:131 Kierman, J., 3:172 Kim, K.-W., 18:87 Kinet, J.-M., 15:279 King, G.A., 11:413 Kingston, CM., 13:407-432 Kirschbaum, D.S. 28:325 Kliewer, W.M., 14:407 Knight, R.J., 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 Kushad, M.M., 28:125
CUMULATIVE CONTRIBUTOR INDEX Lakso, A.N., 7:301; 11:111 Laimer, M., 28:187 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 Lee, J.-M., 28:61 Li, P.H., 6:373 Lill, RE., 11:413 Lin, S., 23:233 Liu, Z., 27:41 Lipton, W.J., 12:69 Littlejohn, G.M., 26:1 Litz, RE., 7:157 Lockard, RG., 3:315 Loescher, W.H., 6:198 Lorenz, O.A., 1:79 Lu, R, 20:1 Lurie, S., 22:91-121 Lyrene, P., 21:xi Maguire, K.M., 25:197 Manivel, 1., 22:267 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 Masiunas, J., 28:125 Mayak, S., 1:204; 3:59 Maynard, D.N., 1:79 McConchie, R, 17:173 McNicol, RJ., 16:255 Merkle, S.A., 14:265 Michailides, T.J., 12:409 Michelson, E., 17:381 Mika, A., 8:339 Miller, A.R, 25:171 Miller, S.S., 10:309 Mills, H.A., 2:411; 9:103 Mills, T.M., 21:105 Mitchell, CA., 17:1 Mizrahi, Y., 18:291,321 Molnar, ].M., 9:1 Monk, G.]., 9:1
CUMULATIVE CONTRIBUTOR INDEX Monselise, S.P., 4:128 Moore, G.A, 7:157 Mor, Y., 9:53 Morris, J.R, 16:255 Murashige, T., 1:1 Murr, D.P., 23:69 Murray, S.H., 20:121 Myers, P.N., 17:1 Nadeau, J.A., 19:1 Nascimento, W.M., 24:229 Neilsen, G.H., 9:377 Nelson, P.V., 26:xi Nerd, A., 18:291, 321 Niemiera, AX., 9:75 Nobel, P.S., 18:291 Nyujto, F., 22:225 Oda, M., 28:61 O'Donoghue, E.M., 11:413 Ogden, RJ., 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; 24:373; 25:197 Ormrod, D.P., 8:1 Ortiz, R, 27:79 Palser, B.F., 12:1 Papadopoulos, A.P., 21:1; 26:239 Pararajasingham, S., 21:1 Parera, CA., 16:109 Paris, H.S., 25:71 Pegg, KG., 17:299 Pellett, H.M., 3:144 Perkins-Veazil, P., 17:267 Pichersky, E., 24:31 Piechulla, B., 24:31 Ploetz, RC, 13:257 Pokorny, F.A., 9:103 Poole, RT., 5:317; 6:119 Poovaiah, B.W., 10:107 Portas, CAM., 19:99 Porter, M.A, 7:345 Possingham, J.V., 16:235 Prange, RK, 23:69 Pratt, C, 10:273; 12:265
481 Predieri, S., 28:237 Preece, J.K, 14:265 Priestley, CA, 10:403 Proctor, J.T.A, 9:187 Puonti-Kaerlas, J., 26:85 Quamme, H., 18:xiii Raese, J.T., 11:357 Ramming, D.W., 11:159 Rapparini, F., 28:237 Ravi, V., 23:277 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, E.A.S., 19:99 Roth-Bejerano, N., 16:71 Roubelakis-Angelakis, KA., 14:407 Rouse, J.1., 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 Saltveit, M.E., 23:x San Antonio, J.P., 6:85 Sankhla, N., 10:63; 24:55 Saure, M.e, 7:239 Schaffer, B., 13:257 Schenk, M.K., 22:185 Schneider, G.W., 3:315 Schuster, M.1., 3:28 Scorza, R, 4:106 Scott, J.W., 6:25 Sedgley, M., 12:223; 22:1; 25:235 Seeley, S.S., 15:97 Serrano Marquez, C, 15:183 Sharp, W.R, 2:268; 3:214 Sharpe, RH., 23:233 Shattuck, V.I., 14:199 Shear, C.B., 2:142 Sheehan, T.J., 5:279
482 Shipp, J.L., 21:1 Shirra, M., 20:267 Shorey, RH., 12:409 Simon, J.E., 19:319 Singh, Z. 27:189 Sklensky, D.E., 15:335 Smith, A.H., Jr., 28:351 Smith, M.A.L., 28:125 Smith, G.S., 12:307 Smock, RM., 1:301 Sommer, N.F., 3:412 Sondahl, M.R, 2:268 Sopp, P.I., 13:1 Soule, J., 4:247 Sozzi, G. 0., 27:125 Sparks, D., 8:217 Splittstoesser, W.E., 6:25; 13:105 Spooner, D.M., 28:1 Srinivasan, c., 7:157 Stang, E.J., 16:255 Steffens, G.L., 10:63 Stern, RA., 28:393 Stevens, M.A., 4:vii Stroshine, RL., 20:1 Struik, P.e., 14:89 Studman, c.J., 19:217 Stutte, G.W., 13:339 Styer, D.J., 5:221 Sunderland, K.D., 13:1 Sung, Y., 24:229 Suninyi, D., 19:263; 22:225; 23:179 Swanson, B., 12:xiii Swietlik, D., 6:287; 23:109 Syvertsen, J.P., 7:301 Tattini, M., 21:177 Tetenyi, P., 19:373 Theron, K.I., 25:1 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
CUMULATIVE CONTRIBUTOR INDEX Upchurch, B.L., 20:1 Valenzuela, H.R, 24:139 van Doorn, W.G., 17:173; 18:1 van den Berg, W.L.A., 28:1 van Kooten, 0., 23:69 van Nocker, S. 27:1 Veilleux, RE., 14:239 Vorsa, N., 21:215 Vizzotto, G., 28: 351 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 Wittwer, S.H., 6:xi Woodson, W.R, 11:15 Wright, R.D., 9:75 Wutscher, H.K., 1:237 Yada, RY., 17:203 Yadava, U.L., 2:1 Yahia, E.M., 16:197; 22:123 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 Ziv, M., 24:1 Zucconi, F., 11:1