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The Peach

Botany, Production and Uses

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The Peach Botany, Production and Uses

Edited by

Desmond R. Layne Department of Horticulture, Clemson University, Clemson, South Carolina, USA and

Daniele Bassi Dipartimento di Produzione Vegetale, University of Milan, Milan, Italy

CABI is a trading name of CAB International CABI Head Office Nosworthy Way Wallingford Oxfordshire OX10 8DE UK

CABI North American Office 875 Massachusetts Avenue 7th Floor Cambridge, MA 02139 USA

Tel: +44 (0)1491 832111 Fax: +44 (0)1491 833508 E-mail: [email protected] Website: www.cabi.org

Tel: +1 617 395 4056 Fax: +1 617 354 6875 E-mail: [email protected]

© CAB International 2008. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data The peach : botany, production and uses /edited by Desmond R. Layne and Daniele Bassi. p. cm. Includes index. ISBN 978-1-84593-386-9 1. Peach--Breeding. 2. Peach--Diseases and pests. 3. Peach-Harvesting. I. Layne, Desmond R. II. Bassi, Daniele. SB371.P42 2008 634’.25--dc22 ISBN:

978 1 84593 386 9

Typeset by AMA Dataset Ltd, UK. Printed and bound in the UK by Biddles, King’s Lynn.

2007045093

Contents

Dedication Contributors

vii x

Preface

xiii

Acknowledgements

xvi

1. Botany and Taxonomy D. Bassi and R. Monet

1

2. History of Cultivation and Trends in China H. Huang, Z. Cheng, Z. Zhang and Y. Wang

37

3. Classical Genetics and Breeding R. Monet and D. Bassi

61

4. Genetic Engineering and Genomics A.G. Abbott, P. Arús and R. Scorza

85

5. Low-chill Cultivar Development B.L. Topp, W.B. Sherman and M.C.B. Raseira

106

6. Fresh Market Cultivar Development W.R. Okie, T. Bacon and D. Bassi

139

7. Processing Peach Cultivar Development T.M. Gradziel and J.P. McCaa

175

8. Rootstock Development G.L. Reighard and F. Loreti

193

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9. Propagation Techniques F. Loreti and S. Morini

221

10. Carbon Assimilation, Partitioning and Budget Modelling T.M. DeJong and A. Moing

244

11.

264

Orchard Planting Systems L. Corelli-Grappadelli and R.P. Marini

12. Crop Load Management R.P. Marini and G.L. Reighard

289

13. Nutrient and Water Requirements of Peach Trees R.S. Johnson

303

14. Orchard Floor Management Systems T.J. Tworkoski and D.M. Glenn

332

15. Diseases of Peach Caused by Fungi and Fungal-like Organisms: Biology, Epidemiology and Management J.E. Adaskaveg, G. Schnabel and H. Förster

352

16. Diseases Caused by Prokaryotes – Bacteria and Phytoplasmas D.F. Ritchie, M. Barba and M.C. Pagani

407

17. Viruses and Viroids of Peach Trees M. Cambra, R. Flores, V. Pallás, P. Gentit and T. Candresse

435

18. Insects and Mites D.L. Horton, J. Fuest and P. Cravedi

467

19. Nematodes A.P. Nyczepir and D. Esmenjaud

505

20. Preharvest Factors Affecting Peach Quality C.H. Crisosto and G. Costa

536

21. Ripening, Nutrition and Postharvest Physiology A. Ramina, P. Tonutti and B. McGlasson

550

22. Harvesting and Postharvest Handling of Peaches for the Fresh Market C.H. Crisosto and D. Valero

575

Index

597

Colour plates 1–73 can be found following p. 144. Colour plates 74–163 can be found following p. 336. Colour plates 164–245 can be found following p. 496.

Dedication

Richard E.C. Layne Richard E.C. Layne served as Research Scientist (1963–1996) and directed the fruit breeding programme (1969–1996) at the Agriculture and Agri-Food Canada Research Centre at Harrow, Ontario. While at Harrow, his scientific research, new cultivar development and outreach efforts significantly impacted the Canadian tree fruit industry and many other temperate, fruit-growing regions around the world. After growing up on the tropical island of St Vincent, West Indies, he attended McGill University, where he earned his BSc degree in Agronomy. Next, he earned MS and PhD degrees in Agronomy from the University, of Wisconsin. His first research experience with fruit crops occurred when he began his new job with Agriculture Canada at Harrow in 1963. During his tenure at Harrow he was responsible for the introduction of 36 new fruit cultivars, ornamentals and rootstocks. Specifically, these included 15 peaches (ten cultivars, three ornamentals and two rootstocks), 13 apricots (12 cultivars and one rootstock), four nectarines and four pear cultivars. In addition to Ontario, these cultivars play significant roles in the fruit crop industries of Michigan, New York, Pennsylvania, New Jersey and various European countries. This vii

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is due, in part, to their improved bud and wood cold hardiness, superior disease resistance, attractive colour, good eating quality and consistency of production. In Ontario, his peach cultivars span the entire ripening season. Those that are currently most widely planted include ‘Harrow Diamond’, ‘Harrow Beauty’, ‘Harson’, ‘Harrow Dawn’, ‘Harrow Fair’ and ‘Harblaze’ (nectarine). His apricots also span the ripening season in Ontario, with ‘Harcot’ and ‘Harogem’ being those cultivars most widely planted. ‘Haroblush’, ‘Harojoy’, ‘Harostar’, ‘Hargrand’ and ‘Harval’ are becoming more widely planted now. His ‘Harlayne’ apricot with natural resistance to Plum pox virus has become a donor of this resistance trait in conventional breeding programmes around the world. ‘Harrow Delight’, ‘Harrow Sweet’ and ‘AC Harrow Delicious’ pears all offer improved tolerance to fireblight. In addition to his cultivar development work, his pioneering work on cold hardiness physiology and applied work on scion/rootstock relationships, peach orchard management and integrated production systems including irrigation have added significantly to the pomological scientific literature. This includes more than 130 publications and six book chapters. He has received numerous research awards and served in important leadership roles during his career. These include the Wilder Silver Medal (1996) awarded by the American Pomological Society (APS) and Outstanding Researcher (1993) by the American Society for Horticultural Science (ASHS). In 1992 he was elected a Fellow of ASHS. He received the Carroll R. Miller award from ASHS in 1977, 1978, 1982 and 1985 for ‘excellence in research dealing with the improved production and utilization of peaches’. He received the Paul Howard Shepard Award for the best paper published by the APS in 1967 and 1982. He was President (1991/2) of the APS and he was also President of the Canadian Society for Horticultural Science (1976/7). He has been an international consultant to the USA, Brazil and China, and participated in an exchange fellowship with INRA, France. As a young boy, I fondly remember going with my dad to his research orchards and seeing and tasting the results of his labours. I had the privilege of learning much about other cultures and the importance of scientific collaboration and exchange while sitting at the dinner table at our home as we hosted scientists visiting my dad from around the world. While in college assisting him in his breeding and orchard management programmes at Harrow, I developed a passion for pomological research and extension that has been the focus of my career. My dad has been and continues to be a great friend, mentor and inspiration; and I fondly dedicate this book to him. Desmond R. Layne

Silviero Sansavini Silviero Sansavini has been Professor of Pomology at the University of Bologna, Italy, since 1974. After growing up on a small fruit farm in the heart of one of the major fruit-growing areas in northern Italy (the Romagna part of the Po Valley), he attended the University of Bologna, where he earned a degree in Agricultural Science. His early career involved a stint as an extension phytopathologist, before being hired at the same university, where he went through the ranks to Full Professor, and served as Chairman of the Department of Fruit and Woody Plant Sciences almost continuously from 1977 to the end of 2007. A ‘man with a mission’, he has promoted the art and science of fruit growing throughout his career by leading many nationally funded research projects and participating in many collaborative international ones, including several funded by the EU. As a natural consequence of this commitment and activity, he has been convener and/or organizer of well over 100 scientific meetings or extension events at the international and national levels. He was elected Chairman of the International Society for Horticultural Science in 1994 and in his 4-year tenure he organized a signal event for horticulture: The World Congress on Horticultural Research (Rome, 1998), the first joint venture carried out by the International Society for Horticultural Science and the American Society for Horticultural Science (ASHS), which marked the first

ix

time that horticulturists from all over the globe had convened to discuss political and economic aspects related to worldwide horticultural research. He has received many awards recognizing his dedication to horticulture: from the National Canners Association Award (assigned by the ASHS for his work on ‘ripening of nectarines and canning peaches’) to the Wilder Medal 2000 awarded by the American Pomological Society, the Gold Veitch Memorial Medal from the Royal Horticultural Society (London, UK) and an Honorary Degree in Horticultural Sciences from the University of Budapest, Hungary. At the national level, he has been recognized by the Italian Ministry of Higher Education. He was named ASHS Fellow in 1995. His editorial activity is tireless. He has been Editor since 1986 of the monthly Italian journal Rivista di Frutticoltura, and is an editorial board member of the following journals: Tree Fruit Production (Binghamton, New York, USA), Fruits (CIRAD, Montpellier, France), L’Arboriculture Fruitière and the International Journal of Agronomy, Agricultural Ecosystem and Plant Genetics (INRA, Montfavet, France). Throughout his career he has edited the proceedings of innumerable symposia and meetings at the international and national levels. He is also Member of several academies: the Italian National Academy of Agriculture, the Italian Academy of Science, a Corresponding Member of the Academie d’Agriculture of France, the Italian Academy of Grape and Wine and the prestigious Academy of ‘Georgofili’ (Florence, Italy). He is author, co-author or editor of more than 500 papers, proceedings and books on biological, physiological and genetic aspects of pome and stone fruits. His in-depth command of very diverse facets of horticultural research is witness to his passionate commitment to horticulture as a whole, his scientific curiosity and his hard-working and demanding attitude, which are the unique traits that have attracted hundreds of students from Italy and abroad to work with him. His students, many of whom have followed his path in research, value the privilege of working with one of the most dedicated, open-minded and challenging personalities of the international fruit science community. Daniele Bassi Luca Corelli-Grappadelli

Contributors

Abbott, Albert G., Department of Genetics and Biochemistry, 116 Jordan Hall, Clemson University, Clemson, SC 29634, USA. Adaskaveg, James E., Department of Plant Pathology and Microbiology, University of California – Riverside, 242 Fawcett Laboratory, Riverside, CA 92521, USA. Arús, Pere, Institut de Recerca i Tecnologia Agroalimentàries (IRTA), E-08348 Cabrils (Barcelona), Spain. Bacon, Terry, Sun World International, Inc., 16350 Driver Road, Bakersfield, CA 93308, USA. Barba, Marina, Instituto per la Patologia Vegetale, Via Bertero 22, I-00156 Rome, Italy. Bassi, Daniele, Dipartimento di Produzione Vegetale, University of Milan, Via Celoria 2, I-20133 Milan, Italy. Cambra, Mariano, Departamento Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Carretera Moncada – Náquera Km 4.5, Apartado Oficial, E-46113 Moncada (Valencia), Spain. Candresse, Thierry, Plant–Virus Interactions, UMR–GDPP–IBVM, INRA Bordeaux-Aquitaine, BP 81, F-33883 Villenave d’Ornon Cedex, France. Cheng, Zhongping, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China. Corelli-Grappadelli, Luca, Dipartimento di Colture Arboree, University of Bologna, Via Fanin 46, I-40127 Bologna, Italy. Costa, Guglielmo, Dipartimento di Colture Arboree, University of Bologna, Via Fanin 46, I-40127 Bologna, Italy. Cravedi, Piero, Instituto di Entomologia e Patologia Vegetale, Piacenza Campus, Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, I-29100 Piacenza, Italy. Crisosto, Carlos H., Department of Plant Sciences, University of California, Kearney Agricultural Center, 9240 South Riverbend, Parlier, CA 93648, USA. DeJong, Theodore M., Department of Plant Sciences, 3037 Wickson Hall, One Shields Avenue, University of California, Davis, CA 95616-8683, USA. Esmenjaud, Daniel, INRA, UMR ‘Interactions Biotiques et Santé Végétale’ (IBSV), 400 Route des Chappes, F-06560 Sophia-Antipolis Cedex, France. Flores, Ricardo, Instituto de Biología Molecular y Celular de Plantas, CSIC/Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, E-46022 Valencia, Spain.

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Förster, Helga, Department of Plant Pathology, University of California, One Shields Avenue, Davis, CA 95616, USA. Fuest, Jaime, Department of Entomology, University of Georgia, 463 Biological Sciences Building, 120 Cedar Street, Athens, GA 30602-2603, USA. Gentit, Pascal, Virology Laboratory, CTIFL, BP21 Lanxade, F-24130 La Force, France. Glenn, D. Michael, USDA–ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Gradziel, Tom M., Department of Plant Sciences, 2055 Wickson Hall, One Shields Avenue, University of California, Davis, CA 95616-8683, USA. Horton, Dan L., Department of Entomology, University of Georgia, 463 Biological Sciences Building, 120 Cedar Street, Athens, GA 30602-2603, USA. Huang, Hongwen, Wuhan Institute of Botany/Wuhan Botanical Garden, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China and South China Institute of Botany/South China Botanical Garden, Guangzhou 510650, People’s Republic of China. Johnson, R. Scott, Department of Plant Sciences, University of California, Kearney Agricultural Center, 9240 South Riverbend, Parlier, CA 93648, USA. Layne, Desmond R., Department of Horticulture, Clemson University, 50 Cherry Road, Clemson, SC 29634-0319, USA. Loreti, Filiberto, Dipartimento di Coltivazione e Difesa delle Specie Legnose ‘G. Scaramuzzi’, Sezione di Coltivazioni Arboree, Facoltà di Agraria, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy. McCaa, James P. (‘Pat’), Del Monte Foods, PO Box 30190, 2716 East Miner Avenue, Stockton, CA 95213, USA. McGlasson, William (‘Barry’), Center for Plant and Food Science (PAFS), University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, South Penrith Distribution Centre, NSW 1797, Australia. Marini, Richard P., Department of Horticulture, The Pennsylvania State University, 119 Tyson Building, University Park, PA 16802, USA. Moing, Annick, Unite de Physiologia Vegetable, INRA Domaine de la Grande Ferrade, 71 avenue Edouard Bourlauz, BP 81, F-33883 Villenave d’Ornon Cedex, France. Monet, René (retired), National Institute for Agronomical Research (INRA), Bordeaux Research Centre, Bordeaux, France. Morini, Stefano, Dipartimento di Coltivazione e Difesa delle Specie Legnose ‘G. Scaramuzzi’, Sezione di Coltivazioni Arboree, Facoltà di Agraria, University of Pisa, Via del Borghetto 80, I-56124 Pisa, Italy. Nyczepir, Andy, USDA–ARS Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA. Okie, William R. (‘Dick’), USDA-ARS Southeastern Fruit and Tree Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008, USA. Pagani, Maria Cristina, BASF Corporation, 26 Davis Drive, Research Triangle Park, NC 27709, USA. Pallás, Vincente, Instituto de Biología Molecular y Celular de Plantas, CSIC/Universidad Politécnica de Valencia, Avenida de los Naranjos s/n, E-46022 Valencia, Spain. Ramina, Angelo, Dipartimento di Agronomia Ambientale e Produzioni Vegetali, University of Padova – Agripolis, Viale dell’Università 16, I-35020 Legnaro (PD), Italy. Raseira, Maria do Carmo Bassols, Empressa Brasileira de Pesquisa Agropecuaria/Embrapa Clima Temperado, Caixa Postal 403, 96001-970 Pelotas, Rio Grande do Sul, Brazil. Reighard, Gregory L., Department of Horticulture, Clemson University, 50 Cherry Road, Clemson, SC 29634-0319, USA. Ritchie, David F., Department of Plant Pathology, North Carolina State University, 2406 Gardner Hall, Campus Box 7616, Raleigh, NC 27695-7616, USA.

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Schnabel, Guido, Department of Entomology, Soils and Plant Sciences, Clemson University, Clemson, SC 29634-0315, USA. Scorza, Ralph, USDA–ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Sherman, Wayne B., Department of Horticultural Sciences, 717 Hull Road, 2133 Fifield Hall, PO Box 110690, University of Florida, Gainesville, FL 32611-0690, USA. Tonutti, Pietro, Scuola Superiore Sant’Anna, Piazza Martiri della Libertà 33, I-56127 Pisa, Italy. Topp, Bruce L., Department of Primary Industries and Fisheries, Agency for Food and Fibre Services, Queensland Horticulture Institute, Maroochy Research Station, PO Box 5083 SCMC, Nambour, QLD 4560, Australia. Tworkoski, Thomas J., USDA-ARS Appalachian Fruit Research Station, 2217 Wiltshire Road, Kearneysville, WV 25430, USA. Valero, Daniel, Department of Food Technology, Head of Post-Harvest and Quality, University Miguel Hernández, Ctra. Beniel – km. 3,2, E-03312 Orihuela, Alicante, Spain. Wang, Ying, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China. Zhang, Zhonghui, Wuhan Institute of Botany, The Chinese Academy of Sciences, Hubei 430074, People’s Republic of China.

Preface

Before the 19th century, many non-Asians believed that the peach originated from Persia (modern-day Iran). Peach probably came to Persia from China along the silk trading routes in the 2nd or 3rd century BC. The Persian origin hypothesis was due, in part, to the fact that peaches were brought from Persia to Europe by the Roman army in the 1st century BC. Alphonse De Candolle in his ‘Origin of Cultivated Plants’ (1885, Appleton and Co., New York, pp. 221–229) contended that peach originated in China. In his tome, ‘The Peaches of New York’ (1917, J.B. Lyon Co., Albany), U.P. Hedrick made the same assertion. In fact, Chinese literature refers to peach more than 1000 years before it first appeared in any European writings. There is documented evidence of peach cultivation in China for more than 3000 years ago. The peach is a symbol of immortality in Taoist mythology. The Queen Mother (goddess) of the West (Xi Wang Mu) had a jade palace that was surrounded by a beautiful garden containing the peach trees of immortality. In the classic Chinese novel, ‘The Journey to the West’ (Wu, Ch’eng-en ~1590 AD, translated by Anthony C. Yu), Sun Wukong, or the Monkey King (picture inset), attained immortality as a result of a memorable visit to this garden: ‘I have been authorized by the Jade Emperor,’ said the Monkey King, ‘to look after the Garden of Immortal Peaches.’ The local spirit hurriedly saluted him and led him inside. The Monkey King then asked the local spirit, ‘How many trees are there?’ ‘There are three thousand six hundred,’ said the local spirit. ‘In the front are one thousand two hundred trees with little flowers and small fruits. These ripen once every three thousand years, and after one taste of them a man will become immortal with healthy limbs and a lightweight body. In the middle are one thousand two hundred trees of layered flowers and sweet fruits. They ripen once every six thousand years. If a man eats them, he will ascend to Heaven with the mist and never grow old.

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At the back are one thousand two hundred trees with fruits of purple veins and pale yellow pits. These ripen once every nine thousand years and, if eaten, will make a man’s age equal to that of Heaven and Earth, the sun and the moon.’ Highly pleased by these words, the Monkey King made thorough inspection of the trees and a list of the arbors and pavilions before returning to his residence. One day he saw that more than half of the peaches on the branches of the older trees had ripened, and he wanted very much to eat one and sample its novel taste. Closely followed, however, by the local spirit of the garden, the stewards, and the divine attendants, he found it inconvenient to do so. He therefore devised a plan on the spur of the moment and said to them, ‘Why don’t you all wait for me outside and let me rest a while in this arbor?’ The various immortals withdrew accordingly. The Monkey King then took off his cap and robe and climbed up onto a big tree. He selected the large peaches that were thoroughly ripened and plucking many of them, ate to his heart’s content right on the branches.

Peach is revered as a delicious and healthy summer fruit in most temperate regions of the world. It is highly perishable but, depending on market demands and fruit availability, it can be a very profitable fruit crop for the careful farmer. Today it is a major fruit crop of commerce in China, Italy, Spain, the USA, and Greece, the top five producing countries, respectively. Currently, there are nearly 1.5 million ha of peaches in production worldwide with the vast majority planted in China (approx. 46%). Tremendous diversity exists within the cultivated peach germplasm for tree size, growth habit, flower size and colour, chill hour requirement, fruit size, shape, flesh texture, flesh colour, flesh acidity, stone adherence to flesh, etc. As a result, many hundreds of cultivars of peaches are grown successfully from climatic and geographic regions as diverse as southern Canada to the highlands of Thailand. Because of the small genome size (about twice that of Arabidopsis), peach has been selected as a model species for studying genomics in the Rosaceae. An extensive physical map/genetic map has been developed and vast genetic information is available through an online database. Marker-assisted selection in conjunction with conventional breeding techniques will undoubtedly lead to new cultivars with enhanced pest resistance, nutritional value and other novel traits. Until a reliable transformation and regeneration protocol can be developed, however, some of the novel genetic advances that have occurred in other fruits and crop plants remain to be fully realized. Management of light interception, careful pruning and training, orchard floor, soil fertility, water availability and crop load are just a few of the many complexities of producing peaches profitably. Combining these factors with the reality that peach is subject to many difficult to manage pests makes it even more of a challenge. Breeding for pest resistance has resulted in some improvements in tolerance to a few diseases and insects, but if trees are left unattended in most locations, they will die prematurely. Thus, careful rootstock and cultivar selection, combined with proper site selection and pest management (monitoring, forecasting, thresholds, cultural and physical controls, biological and chemical control), are vital for success. This comprehensive treatise by 49 research scientists from eight countries summarizes the current state of knowledge in topics ranging from botany and taxonomy to breeding and genetics of cultivars and rootstocks, propagation, physiology and planting systems, crop and pest management and postharvest physiology. The goal was to provide research scientists, extension personnel, students, professional fruit growers and others with a vital resource on peach and its culture. Desmond R. Layne Daniele Bassi

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Des Layne

Daniele Bassi

Acknowledgements

The Editors would like to acknowledge the chapter authors and the following individuals for critical external peer review of chapter manuscripts in this text: T. Beckman, W. Bentley, D. Byrne, J. Clark, J. Cline, K.R. Day, R. Ebel, L. Georgi, J. Girona, R. Gucci, F. Hale, A. Iezzoni, R.E.C. Layne, S. Lewis, A. Liverani, N.W. Miles, A. Naor, M.L. Parker, J.C. Pech, J. Rushing, M. Rieger, E. Sanchez, S. Scott, W. Shane, H. Sherm, C. Xiloyannis and J. Walgenbach. The Editors would also like to acknowledge the following individuals and organizations that helped underwrite the expenses for the colour plate section of the book. In the USA, these included Dr Norman F. Childers, National Peach Council (USA), Al Pearson, Adams County Nursery, the Burchell Nursery, Inc., South Carolina Agricultural Experiment Station, South Carolina Peach Council, Titan Peach Farms and Jerrold A. Watson & Sons. In Italy, these included Apofruit, Apoconerpo, Orogel Fresco, Pempacorer, the Growers Consortium for Crop Development (Newplant), the Crop Research Center (CRPV), the Apulian Nursery Consortium (COVIP) and the Italian Society for Horticultural Science (SOI).

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1

Botany and Taxonomy Daniele Bassi1 and René Monet2 1University

2National

of Milan, Milan, Italy Institute for Agronomical Research (INRA), Bordeaux Research Centre, France (retired)

1.1 Introduction: Origin and Dissemination of Peach 1.2 Species Systematics: Cultivated Peach and Wild Relatives 1.3 Peach Morphology: Description and Variability of the Main Organs Tree Leaf Flower and fruit development Fruit appearance and composition Endocarp (stone, pit) and seed 1.4 Peach Biology and Phenology Floral biology and fruit set Chilling and heat requirements Phenological phases Time of flowering Time of ripening (fruit development period) 1.5 Cultivar Classification Peach description sheet Morphological and commercial classifications Phenological classification

1.1 Introduction: Origin and Dissemination of Peach The botanical name of peach (Prunus persica (L.) Batsch) refers to the putative country of origin, Persia (actual Iran), and Linné (1758) first named the species based on this opinion (Amygdalus persica). Only in the 19th century was the Far East geographical origin (western China) finally acknowledged (De Candolle, 1883; Hedrick, 1917; Vavilov, 1951); written

1 2 3 3 6 11 16 25 25 25 26 27 27 27 29 29 30 30

records and archaeological evidence date peach domestication at least as far back as 3000 BC (Li, 1984). Faust and Timon (1995) gave a detailed account of the possible genetic and geographic origin and dissemination of the peach and related species. Taking into consideration the long history of cultivation of this species and its growing role in several countries over the centuries, many scholars have attempted the classification of the species

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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D. Bassi and R. Monet

and its related forms. Early writings classified almond and peach under the same species, but later they were classified as separate entities (De Candolle, 1883) although possibly sharing the same putative ancestor. The close geographic origin may account for this hypothesis: while peach is native to the Tarim basin north of the Kun Lun mountains, almond is native to the south of the same mountains (beside the northern borders of Afghanistan and Pakistan). The westward movement of peach could have brought it into Persia (actual Iran) in the 2nd to 1st century BC, shortly before the arrival of the Roman army. Early Latin scholars mentioned peaches in Italy in the 1st century BC. The ‘Gallic’ peaches, described of French origin, may account for a possible second, independent arrival of the tree to Europe. Thus, peach could have reached France through the Balkan route almost simultaneously to its arrival in Italy, along the Danube river and the Black Sea region (Werneck, 1956). Additionally, in the Middle Ages, France became probably the second major point of origin after China, according to many records. Peach was brought to the American continent in two different waves. The first was led by the Spaniards, starting in Central America from the first half of the 16th century. In northern America, peaches were later cultivated by the native peoples and propagated by seeds. This early introduction in the Americas has given rise to many landraces, most featuring the non-melting flesh. Some are still cultivated for local fresh markets or even exploited as valuable sources for interesting traits such as ‘evergreen’ (Diaz, 1974) and disease resistance, e.g. powdery mildew or rust (Rodriguez and Sherman, 1990; Pérez et al., 1993). Interestingly, even today, non-melting local cultivars for the fresh market are very popular in southern Europe (Greece, southern Italy and Spain). The second wave of peach introduction in the USA was a direct import from China in the mid-1850s, when the well-known ‘Chinese Cling’ was grown at the Delaware Experimental Station. This tree originated ‘Elberta’, one of the main ancestors of the modern cultivars grown in the USA and elsewhere in the most important peach-growing countries (Okie et al., 1985; Scorza et al., 1985).

1.2 Species Systematics: Cultivated Peach and Wild Relatives The argument about the scientific name of peach was finally set by the classification of Bailey (1927) that grouped all stone fruits under the Prunus genus. Hedrick (1917) stated as not rational a classification of peach species based almost exclusively on the morphological traits of the fruits. Consequently, the species classification based on fruit traits (shape, glabrous skin) or tree growth habit is to be regarded as an early attempt, before Mendel’s laws enlightened the mere intraspecific nature of those singly inherited traits. The following classification is summarized after Knight (1969), Watkins (1976) and Rehder (1990). Peach is included in the Euamygdalus Schneid. section of the Amygdalus subgenus, and can be distinguished from almond (Prunus dulcis (Mill.) D.A. Webb) because the mesocarp of the latter becomes dry and splits at maturity, while the leaves are serrulate. P. persica (L.) Batsch is a diploid species (2n = 16) with a medium tree height (up to 8 m); the leaves are lanceolate, glabrous and serrate, broadest near the middle, with a glandular petiole; the flowers are generally pink, but also white or red; the fruit is pubescent or glabrous, fleshy and the mesocarp does not split; the stony endocarp is very deeply pitted, furrowed and very hard. The main species related to peach are listed below; all of them show fruits with very poor eating quality, although some could be interesting for disease resistance traits or as rootstocks. Prunus davidiana (Carr.) Franch. is a wild species native to north-eastern China, where it is used as a seedling rootstock, given its tolerance to drought, although it is very sensitive to nematodes; the tree is tall (up to 10 m), with a reddish-brown bark; the leaves are long and glabrous, ovate-lanceolate, broadest near the base; the flower is white or light pink; the pit is small and pitted; the flesh is freestone. Accessions of this species have been hybridized with peach to improve disease resistance on scion cultivars to plum pox, powdery mildew, leaf curl, etc. (Moing et al., 2003) or to

Botany and Taxonomy

breed interspecific rootstocks adaptable to marginal soils or to replant problems (Pisani and Roselli, 1983; Roselli et al., 1985; Edin and Garcin, 1994). Prunus ferganensis (Kost. and Rjab) Kov. and Kost. is a wild form found in western China classified as a subspecies of P. persica; a wide variability in terms of fruit types can be found (yellow- and white-fleshed peaches, nectarines, etc.); the leaves have parallel veins and there are parallel grooves in the stone, both single Mendelian traits (Okie and Rieger, 2003). The seed can be cyanogenic glycoside-free (not bitter). It has resistance to powdery mildew. Prunus kansuensis Rehd. is a wild species found in north-east China, also used as a seedling rootstock in China; it is a bushy tree with glabrous winter buds, early-blooming, even so the flowers are considered to be rather resistant to frost (Meader and Blake, 1939); the leaves are villous along the midrib near the base, broadest below the middle; the style is longer than the stamens. The fruit quality is very poor (astringent); the stone is furrowed (with parallel grooves) but not pitted. Prunus mira Koehne is a wild species found in far-west China (eastern Tibet); the tree is tall (up to 20 m) and long-living, up to 1000 years (Wang, 1985); the leaves are lanceolate, villous along the midrib beneath, rounded at base; the flowers are white. The fruit is very variable in shape, colour and size; the stone is smooth, although in some types it resembles P. persica. Some forms are cultivated in Tibet and it is also used as a seedling rootstock in some regions of India. It is reputed as an ancestor of P. persica, having been spread south and east from the Himalayan mountains (Yoshida, 1987).

1.3 Peach Morphology: Description and Variability of the Main Organs

orange-white while young, turning dark orange when older with large lenticels. The tree can live for 20–30 years, but in commercial plantings the average duration is limited to 12–15 years at most, because of either the cultivar becoming obsolete or the loss of productivity. Fruit production begins from the second or third year. Fruiting wood and buds One-year-old shoots are reddish-green, turning dark grey-silver when older. Buds are found at the base of the leaves. Each node normally displays three buds: two lateral flower buds and one vegetative bud in the middle, but up to four or five flower buds can be found and sometimes even more, particularly in the ornamental types. Sometimes only one flower bud is present beside the vegetative, or even only three vegetative buds. There is variability in setting flower buds, where the genotypes with high bud set transmit the character to the progeny with high heritability (Weinberger, 1944); the resulting seedlings tend to be precocious (Rodriguez and Sherman, 1986). Different types of shoots can be found, with different contribution to yield and fruit quality. ●

●

Tree The trunk is straight and smooth, with a reddish-greenish bark in the first year, later becoming dark grey-silver. The root system develops within 50–60 cm in depth, depending on soil type; roots are

3

●

One-year-old shoot: wood of good vigour (50–100 cm) with flower buds along its axis, which ends with a vegetative bud (Fig. 1.1/Plate 1). It is the most important wood in commercial cultivars, since in peach fruit size is positively related to shoot vigour and total current-season wood available (Manaresi and Draghetti, 1915; Marini and Sowers, 1994). Flower bud set may be uneven along the shoot and cultivars may be classified according to basal, middle or apical distribution (Bellini and Scaramuzzi, 1976). Brindle: a 1-year-old fruiting shoot of weak vigour (about 10–25 cm) with flower buds along its axis, which ends with a vegetative bud. This is the most important wood (‘hangers’) for canning peaches, where medium to small-sized fruits are most prized. Feather: side shoot arising from a bud in the same year as that when the bud was formed.

4


Fig. 1.1.

●

●

●

One-year-old fruiting shoots at bloom.

Spur (or dard): a very short (about 1–3 cm), 1-year-old shoot that terminates in a vegetative bud (vegetative spur), eventually surrounded by one or more flower buds (fruiting spur). Water sprout: wood of high (excessive) vigour, with no flower buds. Branch: a limb older than 4–5 years.

Okie (1998) describes a ‘collar’ trait as a swollen collar growing where the shoot attaches to the trunk, resulting in knobs when the shoot is eventually eliminated. The trait seems monogenic and recessive. INTERNODE LENGTH AND DWARFISM. Internode length is influenced by both quantitative and qualitative Mendelian traits. Tree size, however, is predominantly influenced by qualitative traits, independently of the growth habit (see section on ‘Tree growth habit’ below), particularly in the case of the dwarf phenotypes, where internodes are less than 10 mm in length (Fig. 1.2/Plate 2). The regular dwarf tree also features a dense canopy due to larger and thicker leaves. The first dwarf phenotype was described by Lammerts (1945) from the ‘Chinese Dwarf’ peach as recessive and monogenic (Dw/dw). He

also described bushy trees obtained in a ratio of 15:1 by self-pollinating the ‘Babcock’ peach as recessive and controlled by two genes (Bu1/bu1, Bu2/bu2). Hansche (1988) described a more sizereducing dwarf trait than Dw/dw in a progeny from ‘Redcal’ peach (heterozygous for that trait) and reported it as monogenic and recessive (Dw2/dw2). Chaparro et al. (1994) described an even smaller dwarf (Dw3/dw3), with a very thin stem and willow-like leaves. Monet and Salesses (1975) described one more dwarf mutant, smaller than Dw/dw. Heterozygous individuals are semi-dwarf; by self-pollination, these individuals give three phenotypes: normal, semi-dwarf (like the F1 parent) and dwarf with Mendelian proportions 1:2:1. It is a monogenic trait with incomplete dominance (N/n). Gradziel and Beres (1993) reported a similar semi-dwarf as above, featuring internode length half of the standard size, with thicker shoots and greener leaves. The tree is upright but open and with 1-year-old shoots from 30 to 50% shorter than standards. When crossed to standard growth habit genotypes it shows an intermediate heritability (1:1).

Botany and Taxonomy

Fig. 1.2.

5

Dwarf peaches in a commercial orchard.

Okie (1998) described ‘mini-pillar’, a tree form growing upright with wavy twigs where the internode is about half the normal length. TREE GROWTH HABIT. The tree growth habit (or tree form) can be defined as the overall appearance of a tree’s canopy, i.e. the whole set of a tree’s vigour, which could be expressed as the total amount of dry matter or by the rates of shoot growth (quantitative traits) and structural (type of fruiting shoots and their distribution through the canopy, their angle and internode length) traits that determine its natural architecture (Bassi, 2003). For a better understanding of the canopy architecture, two types of branch angle should be taken in consideration: (i) the ‘crotch’ angle, formed by the 1-year-old fruiting shoot (basal part) and the limb from which it grows; and (ii) the ‘extension’ angle, formed by the reference axis (trunk or branch from which the 1-yearold fruiting shoot grows) and the juncture line between the shoot’s point of origin and its apex at full growth (Fig. 1.3/Plate 3). This latter parameter makes it possible to account for the direction of the shoot’s distal part, which, regardless of the crotch angle, can be vertical, upright, outwards (deviating more or less from the vertical), weeping or procumbent

(Scorza, 1984, 2002; Scorza et al., 1989, 2002; Bassi et al., 1994; Bassi, 2003). Several growth habits are known in peach (see a comprehensive list in Chapter 3, Table 3.1). ●

●

●

Arching: similar to the upright (see below), but with a distinct curvature in the 1-year-old shoots (Werner and Chaparro, 2005). Columnar: marked by branches and shoots growing vertically at a notably narrow crotch angle (no more than 35–40°) that makes the tree look like a column (or ‘pillar’). Compact: marked by a large number of lateral shoots and relatively short internodes that produces a dense canopy. The overall shape is semi-spherical for a bush-like appearance. A genetic curiosity, ‘corky triangle’, has been observed in a progeny resulting from a self-pollination of ‘Redhaven’ peach (Monet and Bastard, 1982). A triangular ‘corky’ (necrotic) zone develops close to most buds on the epidermis of the shoot. This character is associated with a lower size of the tree due to a short internode. The ‘Compact Redhaven’ peach studied by Van Well (1974),

6


●

●

●

●

●

●

●

Fig. 1.3. Relationship between crotch (α) and extension angles (β). (From Bassi, 2003.)

Fideghelli et al. (1979) and Mehlenbacher and Scorza (1986) shows this character. It is possible that the ‘corky triangle’ recessive and monogenic (T/t) trait and ‘compact’ tree characters are under pleiotrophic control of the same mutation.

Open: overall tree shape varying from goblet to slightly flat (transversal diameter more developed than the vertical). The 1-year-old fruiting shoots are marked by a wide crotch angle (about 60–70°). Spreading: intermediate between open and weeping. Spur: marked by the prevalence of spurs; the internodes can be shorter than normal, in which case the canopy size could be semi-dwarf or dwarf. Standard: the prevailing growth habit in commercial cultivars; it is marked by medium crotch angle (40–60°) and internode length; canopy shape is generally semispherical or slightly upright (the canopy’s vertical diameter is more developed than the cross-section’s). Twister: a unique branching pattern where after 15–30 cm of growth of the shoot, the phyllotaxy increases from normal 135° to about 180°, with buds and leaves aligned at the opposite sides of the stem, on the same plane; after 15–20 nodes the shoot stops growing and normal shoots break from buds below, repeating the same pattern, i.e. normal first, then twisted; the trait seems monogenic and recessive (Okie, 1998). Upright: the canopy is more developed in height than in width and is larger (in diameter) than the columnar. One-yearold shoots and branches are marked by a relatively narrow crotch angle (about 50°) and vertical growth. Weeping: marked by shoots of medium or wide crotch (larger than 70°) and extended (more than 90°) angles, bending downward (positive geotropic growth), the result being a profile that is gobletlike or more developed in width (Monet et al., 1988).

The main growth habits are sketched in Fig. 1.4 and summarized in Table 1.1. Leaf For peach, new shoots and leaves form following anthesis. Two temporary lateral stipules are found at the petiole base; they abscise when the leaf is fully developed (Fig. 1.5/Plate 4).

Botany and Taxonomy

7

Fig. 1.4. Main growth habit in peach: (a) standard; (b) columnar; (c) upright; (d) compact; (e) weeping; (f) open (from Bassi, 2003).

The leaf blade may be flat or wavy. The wavy blade results from a differential growth of the leaf margins and this is recessive and monogenic (Wa/wa; Scott and Cullinan, 1942); it also has very sharply serrated margins. This leaf character was reported as often associated to a dwarf tree growth habit, with poor set. A narrow-width leaf (willow-like shape) with very serrated margins was reported by Chaparro et al. (1994). This phenotype, designated as Wa2/wa2 and genetically linked to the dwarf gene Dw3, does not have the wavy leaf edges as the original homozygous wa/wa trait, other than showing a narrow width. One more narrow-leaf trait was reported by Okie and Scorza (2002), partially dominant over standard shape (probably several genes are involved), the tree size being sometimes smaller and weaker than standard (Fig. 1.6/Plate 5). Progenies segregate for variable width:length ratio from 10 (narrow) to 0.25% (standard

shape). Narrow leaves show higher water use efficiency than standard (Glenn et al., 2000). There are glands at the margin of the leaf, located at the blade base and at the petiole; three phenotypes are known that show Mendelian inheritance with incomplete dominance, the absence being recessive (E/e; Connors, 1921): (i) reniform (homozygous dominant); (ii) globose (heterozygous); and (iii) eglandular (homozygous recessive) (Fig. 1.7/Plate 6). The leaves with reniform (kidney-shaped) glands have crenate margins, varying in number from two to eight or more, those located on the margin being smaller than those on the petiole. The leaves with globose glands have serrate-crenate margins, but glandless leaves with serrate margins are frequently found on the same tree; the glands are round, smaller than reniform, varying in number from none to over eight, those on the petiole being stalked.

8

Table 1.1.

Characteristics of main growth habits in peach. (Data from a comparative trial in Italy, trees not pruned; from Bassi, 2003.) Tree size (height)

Columnar Upright Standard

Very tall Very tall Medium (regular) Semi-dwarf Dwarf Small Small Small

Open Weeping Compact

Canopy

Angle (degrees from vertical)

Trunk cross-sectional area (cm2)

Height (m)

Width (m)

Crotch (°)

154 ± 16 183 ± 12 180 ± 3.9 76 ± 3.2 59 ± 2.9 230 ± 18 205 ± 25 170 ± 16

5.0 ± 0.5 5.0 ± 0.4 3.6 ± 0.3 2.8 ± 0.1 1.8 ± 0.4 2.7 ± 0.2 2.5 ± 0.2 2.5 ± 0.3

1.5 ± 0.33 2.5 ± 0.3 2.8 ± 0.2 2.3 ± 0.4 2.7 ± 0.3 3.0 ± 0.25 4.2 ± 0.3 3.8 ± 0.33

36.8 ± 7.9 49.6 ± 6.7 59.4 ± 9.3 58.9 ± 8.9 58.2 ± 13.8 65.7 ± 12.0 73.0 ± 12.0 66.7 ± 9.3

Extended (°) 30.8 ± 11.5 41.6 ± 6.5 53.9 ± 13.8 55.2 ± 14.1 60.5 ± 10.2 70.0 ± 19.0 120.0 ± 13.0 71.6 ± 15.5

Internode length (mm) 19.1 ± 2.9 25.1 ± 2.9 28.0 ± 3.0 19.0 ± 3.0 7.5 ± 0.9 23.0 ± 3.0 26.0 ± 0.3 20.0 ± 3.0


Tree form (by crotch angle)

Botany and Taxonomy

Fig. 1.5.

Leaf stipules at petiole base.

Fig. 1.6.

Narrow leaves (left) compared with normal sized. Scale in centimetres.

Marginal reniform glands are pale green, while marginal globose glands are yellow. The eglandular phenotype is associated with a strong susceptibility to powdery mildew (Podosphaera pannosa (Wallr.:Fr.) Braun &

9

Takamatsu), and it is systematically eliminated in breeding operations, although this phenotype could show a good degree of resistance to leaf curl, Taphrina deformans (Berk.) Tul. (Wickson, 1889; Monet, 1983). Cultivars

10

Fig. 1.7.


Leaf glands: (a) reniform; (b) globose; (c) eglandular (note close-up, below).

with globose glands are generally more susceptible to powdery mildew than those with reniform glands (Saunier, 1973). The leaf blade is darker on the adaxial side and the colour of the main veins is related to the flesh colour: yellowish (in yellowfleshed fruits) or greenish-white (in whitefleshed fruits). The ‘redleaf’ trait, first described in a US feral population named ‘Tennessee Natural’, a seedling rootstock (Hedrick, 1917), shows purple-red epidermis, particularly on the young leaves and fruits, while flowers are dark pink (Fig. 1.8/Plate 7). The lamina tends to recover the regular green colour late in the season, but the leaf veins remain purple. Blake (1937) showed that the character is incompletely dominant and monogenic: Gr/gr. At the heterozygous level, the leaves appear copper-red or copper-red green even at the young stage, while when homozygous they are darker red. From observations on ‘Flordaguard’ (homozygous ‘redleaf’) seedlings, two additional ‘redleaf’ phenotypes have been described, suggesting the presence of at least one additional gene (Okie, 1998). In one phenotype the red fades slowly to a bronze colour. In a second phenotype the red fades quickly and

completely (‘quick fade’) to green before leaves attain full size, except the main vein and petiole for some time. In a third phenotype the leaves fade at an intermediate rate, with a red-green mosaic on fading full-size leaves, as in the dominant homozygous. At the end of the season all types fade to completely green. The ‘quick fade’ is reputed as monogenic and recessive.

REDLEAF.

ANTHOCYANIN DEFICIENCY.

The character was first observed on the old US peach cultivar ‘Summer Heath’. The shoots remain green after lignification. Flowers have light pink petals, sepals are green and the fruit skin is feebly pink. The overall anthocyanin content is very low. The character is recessive and monogenic: An/an (Monet, 1967).

ANTHOCYANINLESS. These trees bear white flowers; the receptacle and the sepals are green while the stamens are yellow (instead of reddish). The young shoots remain green even after lignification. The fruits are yellow at maturity without any trace of red pigments (Fig. 1.9/Plate 8). The character was described as recessive and monogenic: W/w (Lammerts, 1945). ‘Anthocyaninless’ is reported epistatic to ‘redleaf’ (Chaparro et al., 1995).

Botany and Taxonomy

Fig. 1.8.

11

Redleaf (left) and greenleaf (right) peach trees.

GREEN APHID RESISTANCE. Resistance to green peach aphid (Myzus persicae Sulzer) was found on a weeping tree (‘Weeping Flower Peach’) and on a seedling rootstock (‘Rubira’) by Massonié et al. (1982). It is a resistance based on a hypersensitivity reaction and the aphid makes only a testing probe on young shoots or leaves. Around the testing site, within a few days, a typical necrotic zone develops (Fig. 1.10/ Plate 9). The trait is monogenic and the resistance is dominant over the sensitivity (Rm1/ rm1; Monet and Massonié, 1994).

Flower and fruit development Peach has hermaphroditic, perigynous flowers. The reddish-green calyx is gamosepalous and falls (‘split-jacket’ or ‘shuck-split’ stage) after the initial swelling of the fruitlet. The inner surface of the calyx, where the nectaries are located, is white-greenish in white-fleshed and yellow to deep orange in yellow-fleshed fruits. The petals are separated and two shapes of corolla are known: (i) showy (rose-shaped) with large petals (Fig. 1.11/Plate 10); and (ii) non-showy (bell-shaped) with small petals, where the anthers emerge from the corolla before full anthesis (Fig. 1.12/Plate

11). Connors (1920) and Bailey and French (1949) studied the inheritance of the flower shape and the non-showy was found to be dominant (Sh/sh), the large-sized showy being dominant over the small-sized showy (L/l). Normally there are five petals, from pure white to dark red, although most cultivars display a pale to dark pink. In ornamental forms pure white and red colours are commonly found, and chrysanthemum-like petals have also been reported (Yoshida et al., 2000) (Fig. 1.13/Plate 12). The number of petals changes according to the semi-double and the double flower traits. In the former phenotype the petal number varies from 12 to 24, the number of stamens transformed in petals being very low. In the latter trait the majority of stamens are transformed in petals arranged in two concentric circles of petals, the inner being darker than the outer, thus conferring the impression of a double flower. The inheritance of double flower is not known but Lammerts (1945) observed that three genes are involved in the semi-double trait: a recessive conditional (d1) and two that modify the number of petals in excess (dm1 and dm2). Examination of the phenotypic

12


Fig. 1.9. Fruit skin colour variability. From top centre going clockwise to the right: a yellow nectarine (anthocyaninless); a white peach (anthocyaninless); a yellow peach (100% blush); a white peach; a non-melting peach; a yellow flat nectarine; a white flat peach; a white nectarine; a yellow nectarine.

Fig. 1.10.

Hypersensitivity reaction on a resistant peach after a proof bite by a green aphid.

Botany and Taxonomy

Fig. 1.11.

13

Flower type: showy.

Fig. 1.12. Flower type: non-showy.

frequencies observed by Lammerts (1945) suggests a simpler explanation with one recessive gene responsible for the presence of supernumerary petals (D1/d1). The genes that regulate the organs’ morphogenesis are

homeotic: their mutation transforms one organ to another. As many as 20 to 30 stamens are attached to the calyx. The anthers are reddish unless male sterility (anthers without pollen) is

14


White, simple

Red, simple

White, semi-double

Red, semi-double

Variegated, white and red

Chrysanthemum-like, red, semidouble

Pink, semi-double Fig. 1.13.

Flower diversity in ornamental peach cultivars. (Courtesy of M. Yoshida, Japan.)

present: sterile anthers look pale yellow instead of reddish before dehiscence. Following self-pollination, some progenies may be male sterile but individuals bearing this trait are typically eliminated from selection. Nevertheless, some male sterile cultivars were largely cultivated, the most famous being ‘J.H. Hale’ because of the outstanding quality of its fruits. Scott and Weinberger (1944) listed a series of cultivars heterozygous for the trait. Male sterility was finally described as monogenic and recessive (Ps/ps; Bailey and French,

1949). A new nuclear male sterility trait was found in ‘White Glory’ (a weeping, ornamental cultivar) which is different from the gene of ‘J.H. Hale’: Ps2/ps2 (Chaparro et al., 1994; Werner and Creller, 1997). Microsporogenesis begins in winter (Knowlton, 1924; Draczynski, 1958) and is followed by meiosis close to bud swell. The gynoecium is superior and it is obviously glabrous in nectarines (see section on ‘Skin adherence and pubescence’ below). Abnormally high temperatures during flower bud

Botany and Taxonomy

initiation may lead to double or triple gynoecium (and pistils), which in turn may eventually give rise to double or triple fruits (discarded during thinning because they are of no commercial value; Fig. 1.14/Plate 13). The eight-nucleate stage of the megagametophyte happens a few days before full anthesis, when the two polar nuclei migrate into the middle of the embryo sac, which elongates after union of the polar nuclei and doubles its length at the time of fertilization. The ovary contains two ovules, but normally only one is fertilized. Time from pollination to fertilization depends on temperature, varying from 24–48 h (Toyama, 1980; Baipo et al., 1989) to 12 days (Herrero and Arbeloa, 1989). The endosperm becomes multinucleate about 10 days after fertilization and cellular after 5–6 weeks (Harrold, 1935; Lilien-Kipnis and Lavee, 1971). Around 8 weeks after full bloom the integuments reach the maximum size (about 20 mm). The first division of the zygote occurs about 2 weeks after ovule fertilization (Harrold, 1935). The embryo fills the testa, absorbing the nucellus and the endosperm in about 100–110 days from full bloom. Thereafter it completes its growth by dry matter accumulation: starch, protein and lipids (about 50%). The ovary (fruit) undergoes four main stages

Fig. 1.14.

Flat fruit, from a double ovary.

15

of growth. The first, rather rapid stage (stage I) is marked by cell division (the length of this phase is nearly the same no matter the fruit development period, FDP). This is followed by a slower stage (stage II) where most of the dry matter is employed in pit hardening and seed and embryo growth (this period is very short in very early-ripening genotypes, where at fruit maturity the stone is incompletely lignified and the embryo does not reach full maturity, in vitro rescue being necessary to recover germination and plant development). The third stage (stage III) is more rapid because cell enlargement and elongation is according to FDP. The last stage (stage IV) is the ripening phase (Lilleland, 1933; Tukey, 1933; Harrold, 1935; Gage and Stutte, 1991). The fruit peduncle remains attached to the shoot after fruit senescence and natural abscission.

Fruit appearance and composition Shape and size (weight) The peach fruit is a drupe. Almost all commercial cultivars share round (globose) or elongated (either oval or more or less oblong)

16


fruits (Fig. 1.15, left and right, respectively/ Plate 14), elongated shapes being dominant over round (Blake, 1932). The flat (or ‘saucer’ or ‘pan-tao’, from the Chinese words ‘flat peach’) fruit, introduced from China, has long been a botanic curiosity in Western countries (Fig. 1.15, centre/Plate 14). The fruit is flattened at opposite poles and the shape affects not only the fruit but also the pit, which is flattened too and rather small. The seed is spherical and has poor germination. The trait is monogenic and dominant over round/elongated: S/s (Lesley, 1940). The homozygous genotype is lethal. Fruit weight varies from less than 50 g in wild forms to 80–110 g for the very, very early-ripening genotypes to over 680 g (Li, 1984), although commercial standards require from 180 to 230 g, depending on FDP and final use. Fruit weight follows a quantitative inheritance. Connors (1922) reported that prepotency in fruit size inheritance depended on parent (Fig. 1.16/Plate 15). Lesley (1957), working on self-pollination up to the seventh generation on several lines, observed an inbreeding effect on fruit size for only one line. Similar findings are reported by Monet et al. (1996), who had no inbreeding effect after three selfing cycles and

Fig. 1.15.

reported a bias towards large size in assessing progenies from parents differing in fruit size. Skin adherence and pubescence Skin adherence to the mesocarp was reported as recessive to non-adherence, even if influence from flesh texture may occur (Lesley, 1957). Two major phenotypes are known about epidermis surface: (i) the standard, fuzzy peach; and (ii) the nectarine, with a glabrous skin. The nature of the nectarine skin character was described as recessive (Rivers, 1906; Blake, 1932; Blake and Connors, 1936) and monogenic: G/g (Bailey and French, 1949). Faust and Timon (1995) indicated that the nectarine mutation probably first appeared in the most north-western part of China, in the Tarin basin (part of the Turkistan region). As early as the 14th century, nectarines were noted in Europe (Gallesio, 2003). From studies of the fuzzless skin trait, three different types of heritable skin surface (at a microscopic level) were described (Fogle and Faust, 1975). One more phenotype, intermediate between nectarine and peach, with a rough surface, was also described. It has a pleiotrophic effect on lack of pubescence (or trichomes) on

Main fruit shapes in commercial cultivars: globose (left), flat (centre), oblong (right).

Botany and Taxonomy

Fig. 1.16.

17

Fruit size gain in F1 progeny from distant-size parents.

dormant buds, which look shiny and smooth (Okie and Prince, 1982). The trait was described as monogenic and recessive: Rs/rs (Okie, 1998). The locus controlling the nectarine trait is probably closely linked to or has a pleiotrophic effect on several other traits. Several nectarine sports, compared with their peach progenitors, often show smaller and rounder fruits (reduced cell number), greater specific gravity, higher soluble solids and organic acids. Other traits may also be involved in the mutation, e.g. the FDP and the chill unit requirement (Wen et al., 1995). The smooth skin of nectarines makes them more susceptible to russeting, mechanical bruising and pest damage (e.g. thrips) than peaches but exploitation of the nectarine trait has led to tremendous advances in peach breeding. During the period from the 1970s to the 1990s, nectarine cultivars became so popular that their profits overtook that of standard peaches. Presently, in some countries such as Italy, their prices have reached a steady level, comparable to the standard peaches. Nectarine features are so distinct that sometimes they are regarded by marketers as an independent species. Indeed, the bright

and glossy over-colour and sometimes distinct flavour play significant roles in driving consumer demand in most markets. Skin and flesh colour Skin (ground) and flesh colour, white or yellow, are among the most popular and commercial criteria for peach cultivar classification, due to the peculiar features of these phenotypes (Figs 1.9 and 1.17/Plates 8 and 16). ‘White’ peaches are revered for their distinct flavour and/or aroma (Robertson et al., 1990), although most of them are either too soft or too susceptible to skin bruising and flesh browning and thus not competitive with the ‘yellow’ types, where carotenoids (the orange pigments) could mask oxidation from bruising or other blemishes. Xanthophylls, the yellow pigments, are synthesized via hydroxylation from carotenoids: lutein from b-carotene, zeaxanthin, antheraxanthin and violaxanthin from bcarotene (Demmig-Adams and Adams, 2002). Carotenoids are photosynthetically active pigments, while xanthophylls dissipate the light excess that can disrupt photosynthesis. Carotenoids and xanthophylls are localized

18


in chloroplasts (chromoplasts) and are found in very small amounts in white peaches. Among carotenoids, b-carotene and b-cryptoxanthin are the primary provitamin A factors, their concentrations reaching around 2000 mg/kg of fresh weight (FW) for the former and up to 3400 mg/kg FW for the latter (Tourjie et al., 1998). Connors (1920) showed that white flesh is dominant to yellow flesh. Bailey and French (1949) suggested the symbols Y/y for the two alleles. Anthocyanins, the glycoside derivatives of the anthocyanidins, are responsible for all colours from blue to red and are localized within the cell vacuoles, in either the epidermis or the flesh. They are synthesized from flavonoids via phenylalanine. The presence of anthocyanins is independent of the skin ground colour, either yellow or white, and can be of quantitative or qualitative origin. The quantitative trait is positively influenced by light exposure and the pigments reach the maximum concentration at full ripening, while the qualitative trait, expressed only in the epidermis, is not related to light nor to ripening and the localization is limited to the skin. There are two indepen-

dent genes regulating the phenotype of qualitative origin. One is the dominant ‘redleaf’ trait (see section on ‘Redleaf’ above); the second is recessive and is expressed in the fruits’ epidermis only, which looks much brighter than in ‘redleaf’, and was designated as Fr/fr (Beckman and Sherman, 2003). A qualitative suppressive trait for fruit red skin, dubbed ‘highlighter’ (H/h; Beckman et al., 2005), was recently reported. When homozygous recessive it completely suppresses the red pigments, but only in the fruit, whereas the w/w trait is characterized by the absence of anthocyanins in any plant tissue. While carotenoids are rather heat-stable, anthocyanins are very labile and subject to browning in canning operations; this has led to the selection for flesh of canning peaches that is anthocyanin-free. Since localization of anthocyanins in skin is independent from that in flesh, commercial canning peaches may or may not develop a red over-colour, given the fruit is peeled before canning. When anthocyanins are present in the flesh, their localization is mainly under the skin and/or close to the pit, the latter reported as dominant over no red (Lesley, 1957). The

Fig. 1.17. Flesh colour variability. From left, top row: non-melting flesh, two yellows (greenish and bright yellow), white; bottom row: red flesh (‘blood’), a yellow melting (anthocyaninless), a yellow and a white melting (flat shape), a white stony-hard (anthocyaninless).

Botany and Taxonomy

amount and distribution of anthocyanins throughout the mesocarp depends on the cultivar (quantitative trait) and may be variably expressed among the fruits on a given tree. Red (‘blood’) flesh peaches One exception to the erratic distribution of the red pigments within the flesh are the ‘red flesh’ (or ‘blood’ flesh) peaches (Fig. 1.18/ Plate 17) and nectarines (Fig. 1.19/Plate 18), where almost all of the flesh is heavily stained by anthocyanins (Gallesio, 1817–1839) independently of the basic flesh colour, either white or yellow (Fig. 1.20/Plate 19). In both types, when the ‘red flesh’ trait is present, the skin has a distinct purple, dull finish. The trait was first described as dominant by Blake (1932), and confirmed by Werner et al. (1998). Flesh compounds influencing flavour and aroma Several compounds contribute to the overall flavour of the flesh: aromatics (volatiles), organic acids, phenolics and sugars are among the most known.

Fig. 1.18.

19

Among the aromatics or volatiles (alcohols, aldehydes, esters, etc.) that contribute significantly to the typical peach aroma, peculiar distribution patterns of hexanal (up to about 740 ppm), trans-2-hexanal (up to about 120 ppm), linalool (up to about 250 ppm), g- and d-decalactone (up to about 130 and 25 ppm, respectively) between white- and yellow-fleshed cultivars were found, with the former showing higher total amounts (Robertson et al., 1990). The main organic acid is malic (over 50% of the total), followed by citric, quinic and succinic acids. When individually analysed, total acids, expressed as malic acid, may range from 0.9 up to about 1.6% FW. Ascorbic acid (vitamin C) content in peach fruits is generally low (below 10 mg/100 g FW), but in some cases it may be threefold higher (Liverani and D’Alessandro, 1999). Sugar content is generally based on assessing the soluble solids content (SSC) by refractometer. This value may reach up to 20% or more, although the average values found in commercial cultivars range from 9 to 15% (Byrne et al., 1991; Crisosto et al., 1998). When individually analysed, total sugars

Red ‘blood’ flesh in peach. (Courtesy of A. Liverani, Forli, Italy.)

20

Fig. 1.19.


Red ‘blood’ flesh in nectarine. (Courtesy of A. Liverani, Forli, Italy.)

Fig. 1.20. Genetic variation for red ‘blood’ flesh trait in peach. (Courtesy of W.R. Okie, Byron, Georgia, USA.)

may reach up to 16% FW; the main sugar being sucrose, ranging from 45 to above 80% of total sugars, followed by either glucose or fructose (Bassi and Selli, 1990; Byrne et al., 1991) and sorbitol; other alcohol-soluble

sugars are in low or barely detectable amounts: inositol, mannose, xylitol and xylose. Low-quality peaches may exhibit a fourfold lower amount of fructose (the sweetest sugar in peaches) and a threefold higher

Botany and Taxonomy

amount of sorbitol but similar SSC compared with high-quality peaches (Robertson et al., 1988). Some genotypes show a distinct low acidity level, resulting in the so-called ‘lowacid’ (LA) trait. In early times, this character was described as an attribute of the ‘honey peaches’ group (Reimer, 1906), easily distinguishable from the ‘acidic’ peaches by a remarkably sweet taste. The trait is well known and regarded in the Far East countries (e.g. China, Japan, Korea), where very sweet fruits are particularly appreciated. From progenies obtained by self-pollination of ‘Redwing’ and ‘Robin’ white peaches heterozygous for the trait, Monet (1979) described the low or sub-acid as a dominant and monogenic character (D/d). The LA phenotype shows mainly citric and malic (about 50%), but also quinic (about 20%) acids in lower concentrations than standard phenotypes, while total acidity is from two- to fourfold lower (0.4 versus 1.4: average values from pooled LA and standard cultivars, respectively). The pH of the LA ranges above 4.0, while in standard phenotypes the pH is below 3.9. The ratio between SSC and titratable acidity (TA) is almost four times higher in the LA phenotypes (Yoshida, 1970; Monet, 1979; Ventura et al., 1995; Moing et al., 1998; Liverani et al., 2003). SSC is comparable to that in the standard phenotype, although LA types show more sucrose and less glucose (Liverani et al., 2003). For a better taste of the LA peaches, SSC above 12% is suggested, in order to overcome the bland feeling of a low acidity coupled with too low sugar content (Delgado, 1998). Nevertheless, the TA of the best-tasting LA cultivars is at least twice that in most of the other LA cultivars (Liverani et al., 2003). Phenolic compounds may play a significant role in flavour because they are responsible for the ‘astringent’ taste. When comparing low- and high-quality white-fleshed cultivars, Robertson et al. (1988) noted that for those rated as unacceptable, there were comparable amounts of sugars and acids but seven times more phenolics than in the high-quality cultivars (120–140 mg/100 g FW). Oddly, even higher phenolic contents (up to 150 mg) found in commercial white peaches of local origin in Italy were rated as acceptable (Bassi and Selli,

21

1990). The discrepancy between these reports may be due to the differences in the aromatic profiles of the cultivars evaluated. It is possible that the very strong aroma of the Italian white peaches partially masked the taste of the phenolics present. Polyphenolic compounds are also responsible for the browning resulting from their oxidation by the enzyme polyphenyloxidase (PPO). Mechanical damage of the cells (skin, flesh) results in the rupture of the vacuoles where the polyphenolic compounds are stored, thus exposing them to enzymatic oxidation by PPO. As a result, quinones are formed that polymerize to brown-coloured pigments. Since these traits are of a quantitative nature, their heritability can be estimated (Hansche and Boynton, 1986) so that cultivars with low susceptibility can be selected. Flesh becomes more astringent in many cultivars under cool summer temperatures (D. Bassi, personal observation). Flesh texture The composition of the cell wall strongly affects flesh texture. So far at least three main distinct phenotypes are known, even if not all is understood in terms of genetic determination and biochemical pathways during the final ripening stages. The first two phenotypes, described by Bailey and French (1932), are the melting (M) and the non-melting (NM). The M texture shows a prominent softening in the last stage (stage IV) of ripening, until a complete melting. Variability in firmness (or rate of softening) is found within this phenotype and Yoshida (1976) distinguished between soft, medium and firm. The ‘firm’ type (FM) softens rather slowly and is less susceptible to bruising during handling, thus allowing an easier management of harvest timing and other grading and shipping operations, and displays a longer shelf life. In addition, it shows a rather high amount of water-insoluble pectins and of Ca bound to the cell wall (Mignani et al., 2006). The NM phenotype (the so-called ‘canning peach’) shows a firm texture when fully mature, softens slowly when overripe but never melts. Rather, it becomes rubbery (because the loss of water) during the

22


senescence stage, when most cultivars could display a peculiar off-flavour (Sherman et al., 1990). However, Beckman and Sherman (1996) noted that it is possible to select for the absence of off-flavours within breeding progenies. The lack of softening in the NM phenotype is related to the loss of endopolygalacturonase (endoPGase) activity, the enzyme responsible for cleaving pectins (polygalacturonic acid chains) from the cell wall in the M fruits (Lester et al., 1996). Morgutti et al. (2006) detected a mutation in the endoPG gene, exploitable for early marker-assisted selection of the trait, even when heterozygous. The melting trait was described to be dominant over the non-melting (M/m; Bailey and French, 1932). See the section on ‘Flesh adherence to endocarp (stone, pit)’ for more details about the inheritance of this trait. M and NM phenotypes develop a rather high amount of ethylene between stage III and stage IV, often more abundantly in NM types (Mignani et al., 2006). The NM flesh is also much less susceptible to mealiness, a rather common storage chilling injury disorder (Brovelli et al., 1998). Recently, a large QTL (quantitative trait locus: a DNA zone containing several genes responsible for a given quantitative trait) for mealiness was detected for the

Fig. 1.21.

endoPG locus, confirming the previous observation that this disorder occurs particularly in M freestone phenotypes (Peace et al., 2005b). The third flesh texture phenotype was first described by Yoshida (1976). He classified a very firm and crispy, ‘stony-hard’ (SH) flesh type as belonging to the M family. However, this type never melts, as in ‘Yumyeong’, a white-fleshed peach from Korea. Its fruit resembles an NM phenotype, becoming rubbery when senescent, and can be either whiteor yellow-fleshed (Fig. 1.21/Plate 20, Fig. 1.22/Plate 21), the only remarkable difference from NM being the almost complete lack of ethylene production (Goffreda, 1992; Haji et al., 2001, 2003; Tatsuki et al., 2006), although it can be stress-induced, as from storage below 10°C (Tatsuki et al., 2006; Gamberini, 2007; Begheldo et al., 2008). The recessive gene was named Hd (Scorza and Sherman, 1996). Water-insoluble pectins in cell walls are rather high, as Ca is bound to them, although its content is variable (Bassi et al., 1998). Stonyhard flesh is often LA, but when progenies are obtained for breeding purposes, and this firm texture segregates with the acidic (nonlow acid) character, a prominent sour taste prevails (J.C. Goffreda, New Jersey, 1997, personal communication).

Stony-hard fruit: white (anthocyaninless) flesh.

Botany and Taxonomy

From the biochemical point of view, the lack of ethylene evolution is due to the transcription suppression (and not to its mutation) of the 1-aminocyclopropane-1-carboxylic acid synthase isogene (Pp-ACS1), a key gene of the ethylene enzymatic pathway (Tatsuki et al., 2006, 2007). From the genetic point of view, the independent inheritance of the SH flesh from M and NM has been demonstrated, also suggesting an epistatic effect of SH, since when exogenous ethylene is applied the SH/M (hdhd/f–) phenotype is induced to melt, while the SH/NM (hdhd/f1f1) keeps firmer, as a standard NM flesh (Haji et al., 2005; see also Table 3.1). From the practical point of view, SH fruits are often very difficult to distinguish from NM or very firm, unripe, M phenotypes. Therefore, evaluation of progenies from controlled crosses segregating for SH is puzzling. SH flesh identification on the tree is very timeconsuming to determine (several passes are required in order to check firmness evolution) and sensory evaluation (by tasting) is not always reliable. So far, the only sound method for SH texture phenotyping is to measure ethylene production (Goffreda, 1992).

Fig. 1.22.

Stony-hard fruit: yellow flesh.

23

Furthermore, there is a possible fourth flesh texture trait (‘very, very firm’), whose phenotype resembles very much the SH flesh in firmness and crispiness, but when fully ripe becomes melting and develops ethylene, although in an unpredictable fashion from year to year (I. Mignani, Italy, 2007, personal communication). This flesh texture, firmer than the ‘firm’ M types, is found in many recently developed new cultivars (both nectarines, e.g. ‘Big Top’, and standard peaches, e.g. ‘Rich Lady’ and ‘Diamond Princess’). It was first commercially introduced from private breeders from California, and is sometimes (e.g. ‘Big Top’ and others) associated with the lowacid trait. Its remarkable keeping quality, particularly on the tree, is a rewarding character for both growers and consumers. However, this flesh type is very difficult to assess, and the same problems as described above for SH flesh phenotyping are experienced. Work is in progress to fully understand this trait, from both the biochemical (physiological) and genetic points of view, since it seems to be a dominant Mendelian trait over the standard M type.

24


A tentative classification of peach fruit flesh phenotypes is presented in Table 1.2. Flesh adherence to endocarp (stone, pit) The flesh may or may not adhere to the endocarp. According to Bailey and French (1932) this trait is controlled by the ‘freestone’ locus, where the freestone (F_) allele is dominant over the clingstone (ff). Intermediate behaviour (semi-freestone or semi-clingstone) with varying degrees of adhesion is observed, particularly in early-ripening genotypes (FDP less than 100 days) (Weinberger, 1950). Rapid flesh maturation, due to early ripening, delays the appearance of the freestone phenotype, thus the semi-freestone phenotypes should be regarded as ‘physiologically clingstone’ but ‘genetically freestone’ (Beckman and Sherman, 1996). Since the intensity of these characters changes during fruit ripening, flesh adherence to the endocarp in early genotypes should be assessed at full ripening or even at the early stage of senescence. Bailey and French (1932) suggested that the flesh adherence to the pit gene and the flesh texture gene were linked on the same chromosome. This was the first published linkage in peach genetics.

However, since in the studied families one phenotype was missing (freestone-NM, as expected by recombination), the Bailey and French interpretation was reconsidered, although semi-freestone peaches with NM flesh have been observed where a thin layer of flesh adheres to the stone (Beckman and Sherman, 1996). The genetic nature of this latter phenotype is not clarified yet, and the semi-freestone trait in NM flesh genotypes should be regarded as of different nature than in M peaches (T.G. Beckman, Georgia, 2005, personal communication). Using the data of Bailey and French (1932), Monet (1989) suggested the three-alleles-one-locus theory. The three following phenotypes resulted: freestone-M (FF, Ff or Ff1), clingstone-M (ff or ff1) and clingstone-NM (f1f1), with dominance from left to right. From recent studies on progenies segregating for endocarp adherence and flesh texture (M and NM), four alleles for the endoPGase enzyme were found responsible for the same three flesh phenotypes as above at a single locus (F): freestoneand clingstone-M and clingstone-NM; the fourth allele is a null-allele (absence) that has the same phenotypic effect as the f1 allele, a mutation that nullifies the enzyme function (Peace et al., 2005a). A diagnostic PCR test was made available to detect all four alleles.

Table 1.2. Tentative classification of peach fruit flesh phenotypes from chemical analysis and sensory evaluation at physiological maturity. (From Yoshida, 1976; Bassi et al., 1998; Haji et al., 2005; Mignani et al., 2006.) Pectinsa Flesh texture

Firmness

Soluble

Insoluble

Calciuma

Ethyleneb

Melting Soft Firm Very, very firmc Stony-hard Non-melting

Low High Very high Very high Very high

+++ +++ ++ + +++

+ ++ ++ +++ +++

++ +++ ++ ++ +++

++ ++ + –/(+) +++

aFlesh

content; no clear-cut threshold between different phenotypes. produced by whole fruits. cSimilar to the ‘stony-hard’, but produces ethylene and becomes melting in the very last stages of ripening (e.g. ‘Big Top’ nectarine). Number of + represents relative content within columns, respectively; – means absence; (+) means traces. bAmount

Botany and Taxonomy

Thus, the Monet (1989) hypothesis of three alleles at the same locus controlling both flesh texture and endocarp adherence was confirmed and the previous theory of Bailey and French (1932), suggesting a linkage between flesh texture and its adherence to the pit, should be rejected. SH cultivars known so far are all clingstone (A. Liverani, Italy, 2005, personal communication).

Fruit ‘keeping’ quality and resistance to manipulation (bruising) ‘Keeping’ quality is related to resistance of the fruit to blemishes caused by excessive softening and refers mainly to firmness of the flesh. Bruising depends mainly on skin resistance to browning; thus a rather firm fruit (flesh) could also be prone to bruises if the skin is too delicate.

25

elliptic (in ovate or elliptic fruit) to roundoblate (in flat fruits). It contains one (exceptionally two) seed(s), whose cyanidic glucoside content makes them taste very bitter. This latter trait is monogenic and dominant over the non-bitter phenotype (Sk/sk; Werner and Creller, 1997) that can be found in some nectarines, e.g. ‘Fantasia’, Early Sungrand’, etc. Although the locus for the nonbitter seed is very close to the nectarine trait (12 cM), it could be recombined with pubescent skin via cross-breeding. Seeds are highly germinable after stratification, their chilling requirement being related to the chilling requirement of the mother tree (Pérez, 1990; Pérez et al., 1993). Viability is hampered in early-ripening genotypes (FDP less than 100–120 days). For these, aseptic embryo culture is needed to ensure germination, allowing rescue of immature embryos as early as 50 days after full bloom (Fig. 1.23/Plate 22) (Tukey, 1935; Ramming, 1985).

Endocarp (stone, pit) and seed The endocarp is lignified, the outer surface being deeply furrowed and pitted. In very, very early-ripening genotypes (FDP less than 55–60 days) lignification is limited and the endocarp may be rather soft, thus allowing consumption of the entire fruit, when the seed is not bitter. Two examples in Italy are ‘Borgia’ and ‘Lucrezia’ (Bassi and Rizzo, 1995). A more or less pronounced ridge is present in the ventral suture, and a needle (very acute tip) could be present at the apex. The latter trait is undesirable in canned peaches because its fragments are difficult to eliminate from processed fruits. Endocarp splitting (at the carpel suture) or shattering (radial fractures) may affect either early- or late-ripening cultivars. Both are commercially undesirable and the former a consumer hazard in eating the stone fragments. While it is possible to select against these undesirable traits, it is reported that cultural practices to improve fruit size (supplemental irrigation, girdling, etc.) may also increase the incidence of endocarp splitting or shattering. The stone shape changes according to the fruit shape, from globose (in round fruit),

1.4 Peach Biology and Phenology Floral biology and fruit set Peach is an insect-pollinated species and it is self-fertile. Even if some genotypes show a low fruit set, no evidence has ever been reported of self-incompatibility as happens in most other Prunus species. Flower fertilization from self-pollination is generally high (ranging from 10 to 90% of fruit set), resulting in a high number of fruitlets (Szabò and Nyéki, 1999); thus crop reduction by fruit removal, i.e. thinning, is required in order to gain commercial fruit size. Even if cross-contamination in closely planted trees may reach around 14–25% (Fogle and Dermen, 1969; Fogle, 1977), cross-pollination under normal conditions is lower than 5% (Hesse, 1975; Fogle, 1977). The only character affecting yield is male sterility, but this trait has been eliminated in presentday commercial cultivars. Some genotypes, mainly nectarines, could be affected by a continuous fruit drop, well after the ‘June drop’, even leading to substantial crop losses.

26


Fig. 1.23. Comparison between mature (left) and immature (right) embryos taken from ‘Spring Crest’ peach at two different stages: the immature embryos fail to germinate under standard stratification procedures and need to be rescued in vitro as the very early-ripening genotypes.

Chilling and heat requirements Chilling requirement is the amount of cold (temperature below a given threshold) required by flower and leaf buds in order to complete morphological development (particularly for reproductive organs) and rest. Several methods have been proposed so far to measure this physiological requirement. The simplest method is that of Weinberger (1950), where the number of hours below 7°C is taken in account. This method is popular worldwide, but it does have some limitations. Richardson et al. (1974), with their ‘Utah model’, defined chilling units (CU), giving specific weight to different temperatures, understanding the role of negation of rest above a given threshold (16°C) before rest completion. A better evaluation of the effect

of fluctuating temperatures and their role in negation of rest in the low-chill areas was given by the ‘dynamic model’ of Erez et al. (1990). While CU can be measured by artificial methods (Dennis, 2003), a simple and cheaper method is to utilize standard cultivar bloom times as an indication of the chilling requirement of unknown genotypes (Scorza and Sherman, 1996). See Chapter 5 for further details. Ranking known genotypes for CU, the lowest level may be around 50 CU (‘FlordaGrande’), up to more than 1500 CU. Analogous to chilling, heat requirements refer to the amount of heat (temperature above a given threshold) after endo-dormancy is fulfilled to achieve organ development, from bloom (Richardson et al., 1974; Citadin et al., 2001) and foliation to fruit maturation.

Botany and Taxonomy

The ‘evergreen’ trait has been described, where the terminal growth never stops (no terminal bud formation) unless killed by frost (Lammerts, 1945; Diaz, 1974), while lateral buds show about 450 CU. The trait, probably due to lack of phytochrome response and resulting from a deletion of the wild type (Bielenberg et al., 2004), was found to be monogenic and recessive: Evg/evg (Rodriguez et al., 1994). In subtropical regions, it allows the yielding of two crops per year. The trait is a candidate model system to study winter dormancy in woody plants (Wang et al., 2003). Phenological phases The peculiar stages of morphological development of the main organs (bud, flower, leaf and fruit) from bud break to leaf fall are termed phenological phases (Fig. 1.24/Plate 23). The occurrence of the single stages (e.g. bud break, full bloom, split-jacket, etc.) plays a key a role in determining specific orchard operations (e.g. the spray schedule against pests and diseases) or in cultivar assessment for the evaluation of their environment adaptability. Time of flowering Time of flowering depends on the CUs necessary to fulfil rest and on the growing degree hour (GDH) accumulation in order to reach full bloom. Even if the two traits are genetically distinct, it is not simple to separate the two components in selection breeding, particularly because the threshold temperatures needed for their fulfilment have not been determined (Scorza and Okie, 1991). Since bloom date is quantitatively inherited and heritability is rather high, breeding could be addressed based on the parents’ behaviour in a given environment, where up to 40 days from the earliest- to the latest-blooming cultivar has been recorded. For further details see Chapter 5. Time of ripening (fruit development period) There is no relationship between flowering and ripening time.

27

While wild peaches exhibit from medium to late ripening, i.e. an FDP from 120 to 210 days from full bloom to the onset of ripening, the FDP of commercial cultivars may range from as early as 55 (Ramming and Tanner, 1987) and 60 days (Bassi and Rizzo, 1995) to as late as 270 days, e.g. some local cultivars from Sicily, Italy (Caruso et al., 1992; Caruso and Sottile, 1999). An interesting ripening mutation (‘slow ripening’) described in progenies of ‘Fantasia’ nectarine hinders completion of ripening (Fig. 1.25/Plate 24). Fruit development is apparently halted before the end of the cell expansion phase (stage III) and the flesh either never softens or softens very slowly, while it keeps a crispy texture (but not of the nonmelting type). The skin ground colour and flesh are greenish and the flavour is very poor, despite lower acidity and higher pH and soluble solids (but similar total sugars) than ‘Fantasia’ (Brecht and Kader, 1984; Brecht et al., 1984). Ethylene and carbon dioxide production are very low, no aroma is developed and the fruits remain firm on the tree even after leaves abscise in autumn. The fruit of this mutant is susceptible to internal breakdown. After ripening-inducing treatments using propylene gas, the fruit eventually becomes soft and advances the onset but not the level of ethylene, without improving the poor texture and flavour. The ripening behaviour seems intermediate between climateric and non-climateric classes of fruits, suggesting a basic similarity between those two categories. The trait was classified as monogenic and recessive (Sr/sr), ‘Fantasia’, ‘Flamekist’ and ‘Fairlane’ nectarines being heterozygous for this trait (Ramming, 1991). Although the trait regulating FDP is clearly quantitative, the presence of major genes can be clearly presumed by two pieces of evidence. First, when measuring the time of ripening in large progenies from distant (in terms of FDP) parents, grouping of offspring in bimodal or trimodal distribution is often observed. Almost all of the offspring ripen within the parental dates, with some seedlings ripening earlier or later (Yamaguchi et al., 1984; Bassi et al., 1988). Second, bud sports, known mutants from commercial cultivars, show FDP that are roughly separated

28


(a)

(c)

-

(b)

Dormant bud

Bud swell (d)

Split-jacket

Small fruitlets (cell division)

(i)

Fruit set (k)

(j)

Pit hardening

(l)

Final swell (n)

(m)

Fig. 1.24.

Late bloom (h)

(g)

Petal fall

(f)

(e)

Full bloom

Early bloom

Fruit veraison

Pink stage

Commercial ripening

(o)

Physiological ripening

Main phenological stages in peach. (Courtesy of E. Bellini, Florence University, Italy.)

Botany and Taxonomy

Fig. 1.25.

Slow-ripening nectarine trees after leaf fall (dormant season).

by weekly intervals, as in ‘Red Gold’ nectarine (Bassi et al., 2004): this opens an interesting insight for genomics in search of QTLs.

●

1.5 Cultivar Classification

●

Several cultivars, local types and landraces have been described in peach. Due to the rather high number of morphological Mendelian traits, the cultivar classification could be addressed under several keys. For the comprehensive list of these traits please refer to Chapter 3. In addition, physiological and quantitative traits of economic importance also play a significant role in horticultural peach taxonomy (phenology). Peach description sheet After Zielinski (1955), Bellini and Scaramuzzi (1976) and Bellini et al. (2007), for a comprehensive characterization of a given cultivar the following organs should be described. ●

29

Tree: see section on ‘Tree growth habit’ above.

●

●

Shoot (on at least 30 one-year-old fruiting shoots, after leaf abscission): length, internode length, number of flower buds/ nodes, flower bud distribution along the stem, bark colour. Flowers (on at least 30 items, at full bloom): type, colour, petal size (length and width), length of the pistil towards the stamens; colour of calyx (inner and outer). Leaf (on at least 30 items collected from the middle section of fruiting shoots, excluding the petiole): colour of the blade (green, purple) and main veins (greenish or yellowish); size (blade length and width), shape (length:width ratio and position of the broadest width referred to the middle); surface (flat, wavy); apical and basal angle of the blade; margin shape (crenate or serrated); glands (eglandular, globose, reniform). Fruit (on at least 30 items): weight; size (length, diameters: suture and cheeks); shape (two sections: along the suture and equatorial); base cavity depth and width; apex shape and tip (or beak, if present); suture (line (no cavity), deep, medium or shallow). Skin: pubescense (absent, light, coarse); red blush (per cent coverage and pattern at physiological ripe stage:

30


uniform, dotted, striped, etc.). Flesh: firmness (by penetrometer); colour (yellow, white); red flesh (‘blood’ trait: present, absent); anthocyanins distribution (under skin, close to the pit, in the middle); flavour (by taste assessment); browning potential; texture (melting, non-melting, stony-hard: for better evaluation of the latter, ethylene production measurement is suggested); fibrousness (fine, coarse, medium); measurement of: sugars (total soluble solids); titrable acidity; pH. Stone: adherence to flesh (air-free, free, semi-cling, cling); size (length, width and breadth); shape; colour; surface (rough, smooth); ridge; grooves and pits; propensity to split or shatter.

FLESH COLOUR

1. 2.

White Yellow

FLESH TEXTURE

1. 2. 3.

Melting Non-melting Stony-hard

FLESH ACIDITY

1. 2.

Acidic Low-acid

Phenological classification CHILLING REQUIREMENT

Cultivars could be classified under several criteria, depending on scope of evaluation.

1. Evergreen (no dormancy under tropical or subtropical climates). 2. From very low (less than 100 CU) to very high (over 1000–1200 CU); most commercial cultivars ranging from 650 to 900 CU.

TREE USE

BLOOM DATE

Morphological and commercial classifications

1. 2.

Fruit production Ornamental (flowers, leaves, growth habit)

FRUIT TYPE (COMMERCIAL)

1. 2. 3.

Peach (pubescent skin) Nectarine (glabrous skin) Canning peach (non-melting flesh)

FRUIT SHAPE

1. 2.

Round/elongated Flat

Could be reported either as the calendar date referred as to that particular place, or as the amount of CU and GDH to accomplish rest and to start blooming. RIPE DATE

As above, it could be recorded as a calendar date, when the very first fruits (5–10%) accomplish physiological ripening (i.e. they become palatable), or as the number of days from full bloom to the onset of ripening (FDP).

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2

History of Cultivation and Trends in China Hongwen Huang,1,2 Zhongping Cheng,1 Zhonghui Zhang1 and Ying Wang1

1Wuhan

Botanical Garden/Wuhan Institute of Botany, Chinese Academy of Sciences, People’s Republic of China 2South China Botanical Garden, Guangzhou, Chinese Academy of Sciences, People’s Republic of China

2.1 Origin of the Peach 2.2 History of Peach Cultivation in China Pre-Qin Dynasty (1100–221 BC) Eastern and Western Han Dynasty (222 BC–220 AD) From Wei–Jin Dynasty to Sui–Tang Dynasty and Five Dynasties period (221–960 AD) Song, Yuan, Ming, Qing Dynasties and Republican period (961–1948 AD) 2.3 Current Status of Chinese Peach Production and Trends in China Peach germplasm collection, repositories, evaluation and utilization in China Main peach cultivars, peach production and growing regions in China Rapid development of greenhouse production Peach postharvesting, processing and marketing in China Problems faced by the Chinese peach industry Current trends of Chinese peach production 2.4 Summary/Conclusion

2.1 Origin of the Peach The peach originated in China (Wang and Zhuang, 2001), where it is a symbol of long life (Fig. 2.1/Plate 25). Numerous pieces of evidence have revealed that China has the longest history of peach cultivation in the world. One discovery demonstrated that peach growing in China dates back to Neolithic times. When a Neolithic village site was discovered in Hemudu village, Yujao city, Zhejiang province in 1973, finds included wild peach stones dating back to 6000–7000 BC

37 38 38 40 40 42 44 44 45 48 49 51 52 57

(Chen, 1994). A similar archaeological finding in Taixi village of Gaochen city, Hebei province, at the site of ruins from the Shang Dynasty (1600–1100 BC), revealed two peach stones measuring 1.6 cm × 1.0 cm and 2.0 cm × 1.2 cm. Their shape, size and surface groove patterns were almost the same as those of current peach cultivars in China. An expedition conducted by the Chinese Academy of Sciences during 1973–1976 discovered tremendously diverse genetic resources of wild peach that are still widely grown in large areas of China, including Tibet, Gansu, eastern Shaanxi,

© CAB International 2008. The Peach: Botany, Production and Uses (eds D.R. Layne and D. Bassi)

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south-eastern Tibet. Some trees having trunk circumferences of about 6 m appeared to be more than 300 years old. A fruit tree survey team of the Tibet crop resource expedition during 1981–1982 also found an ancient Tibetan peach tree with a height of 21 m and a trunk circumference of 10 m, which was believed to be more than 1000 years old. This tree was located in Changdu region of Tibet, where the Hengduan Mountains–Sanjiang (Three Rivers) area was being geo-botanically investigated (Duan et al., 1983). Obviously, Tibet and Gansu province, where P. mira and Prunus kansuensis Rehd. are native, should be regarded as one of the original native centres for peach. The peach has a remarkably extensive distribution throughout China: from Taiwan and southern Guangdong provinces in the subtropics, to cold temperate regions as far north as in Yanbian, Jilin province (Wang and Zhuang, 2001); from the west and southwest regions as far as Xinjiang and Tibet autonomous districts, to east regions as far as all coastal provinces in China. However, commercial peach cultivation is limited within the latitude range of 23–50°N (Fig. 2.2/Plate 26).

2.2 History of Peach Cultivation in China The peach is one of the most ancient domesticated fruits in China. As early as 4000 years ago, the value of peach had been recognized and exploited by the Chinese with extensive efforts on natural selection and domestication. Several unique historical phases of Chinese peach domestication and cultivation are summarized in the following. Pre-Qin Dynasty (1100–221 BC) Fig. 2.1. A Chinese painting by Ma Tai (1885– 1935), telling a story that an old man with white hair but a young, boyish face always steals peaches. People make fun of this long-lived man, but he explains ‘Peach is good for my health’.

southern Henan, south-western Sichuan and western Yunnan provinces (Qu and Sun, 1990). Tibetan peaches (Prunus mira Koehnes) were found in Jiacha and Lang counties of

There may be even earlier descriptions of peach in ancient Chinese texts. ‘桃 pronounced Tao’ (Chinese name for the outdated genus Amygdalus) refers to peach and is described in the ShiJing (The Book of Odes or The Book of Songs), written between 1100 and 600 BC (Anon., 11th–6th century BC). The tao is described in the ShiJing – Weifeng chapter as ‘Peach growing in garden, its fruit for eating’, indicating that peach was cultivated in China

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Fig. 2.2. Chinese peach production regions: (I) north-west drought region; (II) northern China plain region; (III) Changjiang River humid region; (IV) Yunnan–Guizhou high plateau cold region; (V) Qinghai–Tibet plateau cold peach region; (VI) north-eastern China cold region; (VII) southern China subtropical region.

3000 years ago. In the ShiJing – ZhouNan chapter, the biological characteristics of peach are concisely described as ‘桃之夭夭，灼灼其华。桃之夭夭，其叶蓁蓁。桃之夭夭，有贲其实’, illustrating beautiful fire-like flowers when blooming, flourishing foliage and dense fruiting, symbolizing a family’s prosperity, happiness and luck. The ShiJing –DaYa chapter describes peach as ‘投我以桃，报之以李。园中有桃，有贲其实’, clearly evidencing that peach was widely cultivated and fruit were produced plentifully during that time. Later,

a historiography book LüShiChunQiu (300 BC) depicts peach blooming in spring as ‘仲春之月桃始华’ (Lü, 300 BC). The earliest illustration of peach cultivation and ecological requirements in Chinese ancient literature probably occurs during the Zhanguo period (Warring States, 500–300 BC). In the encyclopaedia GuanZi – DiYuan volume (Guan, 5th century BC), it is written ‘五沃之土，宜彼群木，其桃其李’, explaining that peach cultivation requires good soils and peach responds to high fertilization. It concisely illustrates a

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relationship between peach growth and soil conditions. In addition, HanFeiZhi – WaiChu volume 33 (Han, 280–233 BC) describes ‘子产治郑，桃李之荫于街者莫援也’, which explains that besides use as edible fruits, the peach was also used for landscaping as a shade tree in the current Xinzheng area, Henan province. During this pre-Qin Dynasty period, peach was widely grown in southern China. According to the Chinese Agricultural Archaeological Plate Collection, peach stones have been discovered at many archaeological locations in southern China, from the Eastern Zhou Dynasty (770 BC) at Jiangling, Hubei province and from the Zhanguo period (Warring States, 475–221 BC) at Pujiang, Sichuan province and at Hezhang, Guizhou province. Eastern and Western Han Dynasty (222 BC–220 AD) During this historical period, cultivar selection and cultural techniques were developed, resulting in a new era of peach domestication in China. Fifteen records related to peach are identified in ShiJi (a history annals, 100 Bc) (Sima, 1st century BC), 19 records in HanShu (history annals of the Han Dynasty, 1st century AD) (Ban, 39–92 AD) and 14 in Post-HanShu (history annals of the late Han Dynasty, 3rd century AD). These records encompass a variety of peach-related delineations from town and street names, mountain and river names and even official titles. In ErYa (ancient dictionary for terms and names) – Shimu chapter (notes in trees) (Anon., 2nd century BC), there are records of species, varieties and cultivars for peaches described as ‘旄，冬桃’ and ‘榹，山桃’, indicating the two most important species of Prunus persica and Prunus davidiana of modern peach production. In XiJingZaJi (a miscellanea) edited by Ge Hong (Ge, 1st century AD), the fruit trees in the emperor’s garden (current Xian, Shaanxi province) are described, including many peach varieties: ‘Qin Tao’ (Shaanxi peach), ‘Si Tao’ (peach), ‘Xiang He Tao’ (locally named peach), ‘Shuang Tao’ (frost peach), ‘Jin Cheng Tao’ (locally named peach), ‘Qi Di Tao’ (fancy petiole peach) and ‘Zi Wen Tao’ (purple paper peach).

Thus, many locally selected peach varieties existed in China more than 2000 years ago. The relationship of peach blooming to local climate is written in Pre-HanShu (dynasty annals) – GouXu Records as ‘桃方华时，即有雨水，. . . . . ，谓之桃花水耳’, . indicating a very similar rainy season during P. persica blooming as normally occurs at the present time in south and south-central China. Peach culture techniques were also developed during this period. SiMinYueLing (farming calendar) written by Cui Shi during the Eastern Han Dynasty (Cui, 2nd century AD) provides ‘正月…自朔及晦可移诸树，. . . 唯有果实者及望而止’, indicating that peach trees should be planted or transplanted in January in the Lunar calendar, but fruiting trees should not be transplanted. It clearly suggests that peach planting should be done in February and good peach production requires fertile soils. Wang Bao even records a high-density planting of peach in TongYue from the Western Han Dynasty (Wang, 1st century AD), stating ‘种植桃、李. . . . . ，三丈一树，八尺为行，果类相似 . ，纵横相当’ that suggests a 6.93 m × 1.85 m spacing.

From Wei–Jin Dynasty to Sui–Tang Dynasty and Five Dynasties period (221–960 AD) The traditional Chinese peach culture was established during these centuries. New production techniques were advanced and new uses for peaches were further exploited. First, peach cultivar development by seedling selection and domestication of wild trees resulted in a large number of new cultivar releases. For example, GuangZhi written by Guo Yigong in the Eastern Jin period (Guo, 4th century AD) records ‘there are winter peach, summer white peach, autumn white peach and many local peaches cultivated in low reach region of HuangHe (Yellow River), among many beautiful peaches having an outstanding autumn dark-red peach’. YeZhongJi written by Lu Hui in the Western Jin period (Lu, 3rd century AD) describes ‘a hook-nose peach weighting one kilo growing at ShiHu garden’ (currently LinZhang region, Hebei province). During the Northern Wei period (386–534 AD), a very famous book QiMinYaoShu (encyclopaedia


for living) written by Jia Sixie (Jia, 533–544 AD) lists more than ten cultivars previously described and also adds a new variety, ‘Nai Tao’. In addition, from the Wei–Jin period, records of high-quality peach cultivars are found in TaoFu (peach poetry) by Fu Xuan (Fu, 2nd century AD) in Western Jin, such as ‘early summer ripening’, suggesting an existence of early cultivars, and ‘sweet and crispy’ for nonmelting peaches. Furthermore, selection and cultivation for ornamental and yellow-fleshed peaches are recorded during the Tang Dynasty (618–907 AD); for example, KuaiYuanTianBaoYiShi (a historiography book) describes a ‘new ornamental peach with thousand-leaf like flowers was introduced into the Emperor’s garden’. TangShu (history annals of the Tang Dynasty) records: ‘In ZhenGuan 21 [Tang Dynasty calendar, 647 AD], western KangJu country [now the north-west Xinjiang autonomous region] pays tribute to a goose-egg sized and gold coloured peach, called “golden peach”’. Second, knowledge about tree biology and propagation was extensively improved, setting the foundation for the traditional system of Chinese peach cultivation. QiMinYaoShu (encyclopaedia for living; Jia, 533–544 AD) summarizes a cultivated peach tree life cycle that is very similar to modern peach production. ‘桃性早实，三岁结子，七八年便老，老则子细，十年则死’ illustrates that peach is precocious, fruiting at age 3 years, production declines at age 7–8 years when fruits are getting smaller, and trees die in 10 years. For seed germination and seedling propagation, seed stratification was well understood and traditional methods were well developed at this time. These are illustrated in QiMinYaoShu: ‘桃熟时，于墙南阳中暖处，深宽为坑。选取好桃数十枚，劈其核，即内牛粪中，头向上，取好烂粪和土厚覆之，令厚尺余。至春桃始幼时，徐徐拨去粪土，皆应生芽，合取核种之，万不一失。其余以熟粪粪之，则益桃味’, indicating that seed stratification was crucial to embryo development for seed germination and that fermented manures are good both for seed stratification and for improvement of peach fruit flavour and overall quality. In addition, a layering propagation method is also developed and summarized in the book, detailing shoot types and soils that should be used.

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Third, planting and transplanting are precisely summarized in QiMinYaoShu as ‘以锹合土掘移之’, encouraging planting and transplanting seedlings with soil balls holding the roots. Various peach pruning methods had also been developed and are documented in the book, such as the application of girdling or mechanical injury to the tree trunk to suppress vegetative growth, increase fruiting and raise production. Some of these methods are concisely illustrated in QiMinYaoShu as ‘桃性皮急，四年以上，宜以刀竖其皮’, explaining that the ring bark method should not be used until trees are 4 years old and cutting should be careful on the bark. This demonstrates that ancient Chinese peach growers had a good understanding of tree reproduction biology and management practices in peach production. Finally, frost protection and pest control techniques were developed along with practices in peach orchard management. This overall frost protection method for all fruit trees including peach is well documented in QiMinYaoShu (Jia, 533–544 AD) as ‘凡五果（包括桃树）花盛时遇霜，则无子。常预于园中，往往贮恶草生粪，天雨新晴，北风寒切，是夜必霜。此时放火作熅，少得烟气，则免于霜矣。’, illustrating that all five kinds of species (including peach) are vulnerable to frost damage during blooming. Frost damage to flowers will cause production failure. To prevent frost damage, orchards need to be stored with straws and manures. Whenever a halt in rain occurs with a clean sky and cold wind from the north, it signals an overnight frost. Burning straw mixed with manures and releasing smog will prevent frost damage. This smoking method for preventing flower frost is still one of the major applications widely used in peach orchards in northern China. Application of pest control measures also began during these centuries. As documented in QiMinYaoShu: ‘凡五果及桑正月一日鸡鸣时，把火遍照其下，则无虫灾’, saying that in cultivation of the five kinds of species and mulberry, lighting up the overall orchard using torches in the Chinese New Year will prevent insect damage. In fact, this idea and method underline the principle that the current application of ultraviolet light for insect control is based on. The above ancient Chinese literature during the time of the Wei–Jin to Sui–Tang

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dynasties and the Five Dynasties period probably sheds light only on the tip of the iceberg of a rich Chinese peach cultivation history, abundant natural resources and welldeveloped understanding of cultural technology. Some historical knowledge about germplasm resources, tree biology, propagation and orchard management is still worthy of further study. Song, Yuan, Ming, Qing Dynasties and Republican period (961–1948 AD) During these 1000 years, domestic and international exchanges in agriculture played an important role in Chinese peach production and development. Peach production regions were continuously expanding and many new production regions were developed. As information and technology was spread domestically, and to some extent abroad, peach culture developed further during this time. Over many years, Chinese peach growers systematically domesticated and continuously selected improved germplasm. This resulted in substantial improvements of peach culture and production in China. For example, LuoYangHuaMuJi (LuoYang flower and tree collections) written by Zhou ShiHou (1081 AD) records 30 peach varieties: ‘Xiao Tao’ (small peach), ‘Shiyue Tao’ (October peach), ‘Dong Tao’ (winter peach), ‘Pan Tao’ (flat peach), ‘Qianye Tao’ (thousand-leaf peach), ‘Chan Tao’ (twisted peach), ‘Erse Tao’ (doublecoloured peach), ‘Hehuan Erse Tao’ (dualcolour happiness peach), ‘Qiangyefei Tao’ (thousand-leaf pink peach), ‘Dayu Tao’ (big royal peach), ‘Baiyu Tao’ (white royal peach), ‘Jin Tao’ (golden peach), ‘Yin Tao’ (silver peach), ‘Bai Tao’ (white peach), ‘Kunlun Tao’ (Kunlun Mt. peach), ‘Hanli Tao’ (big peach), ‘Yanzhi Tao’ (crimson peach), ‘Zao Tao’ (early peach), ‘You Tao’ (smooth and waxy skin peach), ‘Renmian Tao’ (people face peach), ‘Mi Tao’ (honey peach), ‘Pingding Tao’ (nontip peach), ‘Pang Tao’ (fat peach), ‘Ziye DaTao’ (purple-leaved big peach), ‘Li Tao’ (gift peach), ‘Fang Tao’ (square peach), ‘Fenzhou Tao’ (local township named), ‘Putian Tao’ (local township named), ‘Hongrang Tao’ (red-fleshed peach) and ‘Guang Tao’ (non-pubescence peach).

The honey peach (typical southern, melting, low-acid type) and the non-tip peach are probably the progenitor varieties that all southern Chinese peaches are derived from. The Yuan Dynasty’s WangZhen’s Farming Book written by Wang Zhen in the 14th century (Wang, 1313 AD) lists two additional early peach varieties, ‘Luosi white’ (fine white) and a late variety ‘Guoyan red’ (passing wild goose red). The most famous Chinese pharmacopoeia is the BenCao GangMu written by Li Shizhen during the Ming Dynasty (Li, 1578 AD), which classifies peach varieties by colours, fruit shapes and maturity date into different categories, saying ‘桃品种甚多，其花有红、紫、白、千叶二色，其实有红桃、绯桃、碧桃、缃桃、白桃、乌桃、金桃、银桃、胭脂桃，皆以色名者也；有锦桃、油桃、御桃、方桃、匾桃、偏核桃，皆以形名者也；有五月桃、十月冬桃、秋桃、霜桃，皆以时名者也’, meaning that there are many varieties of peaches. The flower colours vary from red, purple, white to double colours. The fruit colour variations range from red to pure white. Varieties are named after their colours (including pink peach, light-pink peach, crimson peach, red peach, dark-red peach, purple peach, golden peach, silver peach and white peach); also, they are named after their shapes and appearance (including tip peach, smooth peach, royal-type peach, square peach and flat peach); in addition, some are named after their maturity (including May peach, October peach, autumn peach, winter peach, etc.). Slightly later at the end of the Ming Dynasty, QunFangPu (Florilegium) written by Wang Xiangji (Wang, 1621 AD) gives detailed descriptions for some known cultivars, besides listing previous cultivars; for example, flat peach is described as ‘shape like a cake, taste sweet’. It also records details about Shanghai honey (melting) peach as ‘it is native to Shanghai, but best peaches are produced from the GuShangBaoXi garden with sweet taste little less than lychee’. ShuiMiTaoPu (melting honey peach register) by Chu Hua in the Qing Dynasty (Chu, 1813 AD) records: ‘Melting peach was from the Gu’s fragrance garden in Ming Dynasty, it is juicy and tastes sweet, so called melting peach’. The origin of this type of peach was unknown, but probably derived from peaches from Beijing or Kaifeng.


Peach production in the Qing Dynasty was further expanded and some major production regions included Taiyuan, Shanxi province; Kaifeng, Luoyang, Shangqiu, Henan province; Chengdu, Sichuan province; Hangzhou, Zhejiang province; Hejian, Shenxian, Suning, Hebei province; Feicheng, Shandong province; and Nanhui, Baoshan, Shanghai city. Until the Republican period (1920s), new peach production regions were developing very rapidly, extending into many new areas including Wuxian, Wuxi, Yangzhou, Zhenjiang, Jiangsu province (eastern China); Suzhou, Dangshan, Anhui province (central eastern China); Ningling, Yanshi, Henan province (central northern China); Fenghua, Zhejiang province (eastern China); Zibo, Shandong province (northern China); Taigu, Shanxi province (north-western China); and central Shaanxi and eastern Gansu province (western China). During these ten centuries, peach culture technology had also developed to a new level. The documentations recorded in the Chinese literature are also more detailed. For example, NongSangYiShiZuoYao (farming, clothing, dieting abstracts) written by Lu Mingshan in the Yuan Dynasty (Lu, 1314 AD) describes how peach trees should be planted as ‘桃树栽时提根与地平，使侧根舒畅易活’, explaining that when planting a tree, holding the tree and making its lateral roots spread will improve the survivability. In ZhiBenTiGang written in the Qing Dynasty, Yang Shen (Yang, 1774 AD) illustrates more precisely that successful planting of peaches depends on a good understanding of root–shoot balance: ‘Planting: if a tree has more shoots and less roots, shoots need to be thinned; or if a tree has less shoots and more roots, then roots need to be thinned’. This documented how to maintain a balance between shoots and roots. ‘The peach seedlings should be planted in spring time when they are still in dormancy, otherwise, trees should be planted in autumn when their leaves fall off. Planting pits need to be deep and wide for root spreading and development, watering planted trees sufficiently and returning the surface soil on to the roots slowly will ensure soil to be settled on roots well’. This is not surprising because largescale peach planting and production growth occurred during this time. Evidently, ancient

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Chinese peach growers gained rich experiences from these 1000 years of cultivation and they greatly improved their understanding of peach tree physiology. They summarized the relationship between successful planting of peach trees and the growth balance of root and shoots. During the same time, propagation and orchard management techniques had been greatly developed, noted in ShuiMiTaoPu (juicy peach register) as ‘桃树生二，三年可接，多在春分前，秋分后，高树根二，三尺许锯去，以快刀修光，使不沁水，又向靠皮带膜处（韧皮部与形成层接合部），以上切下一寸余，却以水蜜桃东南北枝两边削成马耳状者，在口中含热插下，用纸封固，外涂以泥，在加匿叶护之’, saying that the peach can be grafted on 1- or 2-year-old seedlings, usually before vernal equinox or after autumnal equinox. The seedling top is cut off at 60–90 cm from the ground using a sharp knife and a cut between bark and wood about 3–5 cm is made. The scion-wood should be collected from the east or south side of the canopy of the mature ‘juicy peach’. A mouse-ear shaped piece is cut from buds of the scionwood and inserted into the cut of the seedling (the scion piece can put in the mouth for warmth and moisture), and then wrapped with paper and soil slurry. The grafting techniques for peach propagation were well developed during this time. Also, orchard management in southern China was well understood during this period as described in this book: ‘the peach growing in the south usually suffers waterlogging that resulted in root rot and orchard failures during rainy season. Deep ditches are needed for good drainage and fruit quality. The peach is drought tolerant but sensitive to waterlogging, welldrained orchards produce large and high quality fruits’. The characteristics of peach loving full sun and good drainage and drought tolerance are well documented. Good orchard practice for high yields and high quality had been developed in almost all major peach production regions in China during this time. Throughout the 4000-year history of peach cultivation, Chinese peach growers have made significant contributions to peach domestication and peach industry development through exploring wild germplasm,

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selection and cultivar development, development of thorough understanding of tree physiology and development of many important cultural practices. China’s rich heritage of peach cultivation is worthy of great appreciation worldwide and of study by modern pomologists.

2.3 Current Status of Chinese Peach Production and Trends in China Peach is one of the top five most important fruit tree crops in China. Since China became the largest peach producer in the world in 1994, peach planting and production have increased steadily up to 1.4 million ha and 4.38 million t in 2003. Of this production approximately 80% was in white-fleshed melting peach cultivars and 20% in other cultivars. The total area planted in China has remained static at around half the world total of 2.2 million ha in recent years. The massive production of Chinese apples and pears is having a marked effect on world supplies and trade in pip fruit and fruit juices. The increase in peach production could likewise have a similar impact on the international market. Peach germplasm collection, repositories, evaluation and utilization in China The national peach germplasm survey conducted during the 1950s has played an important role in current germplasm collections and repositories. Five species and 16 varieties and forms were identified within subgenus Amygdalus of genus Prunus. In addition, 800 traditional landraces and cultivars were documented (Wang et al., 1989; Guan and Wang, 1993). These efforts have resulted in the establishment of three national peach germplasm repositories in Beijing, Zhengzhou and Nanjing. Local efforts in peach germplasm collection also occurred simultaneously in Shanghai, Dalian and Shanxi. Altogether, more than 1000 germplasm accessions have been collected and maintained to safeguard against genetic erosion or complete loss due to recent rapid changes in the Chinese economy and society (Wang et al., 1989). The efforts, together

with active programmes in screening and evaluation, continued throughout the 1990s. In addition, a number of foreign cultivars were introduced to China, such as ‘Kanto 5’ and ‘Myoujou’ from Japan, and ‘NJN’ and ‘Babygold’ from the USA. In China, the peach national repositories also serve as breeding centres. Many new varieties have been developed from these three national and other local repositories. The repositories also conduct joint efforts in evaluation of the existing germplasm, particularly some unique genotypes. For example, the Fruit Germplasm Checklist (edited by the Fruit Research Institute of the Chinese Academy of Agricultural Science, 1993, 1998) lists 648 good peach genotypes (landraces) with detailed information on place of origin, fruit maturity, fruit size, flesh characteristics, free- or clingstone, soluble solids, soluble sugars and acid, vitamin C, pollen viability, and other unique characteristics and uses. Screening and evaluation efforts at the repositories have resulted in a marked increase in the understanding of special genotypes and the effective use of germplasm. First, some commercial cultivars have been selected directly from those superior genotypes and used in peach production, such as the northern variety ‘Feicheng Tao’ with big fruit size and good transportability and storage quality, as well as ‘Shenzhoushuimi’ (Shengzhou melting honey), ‘Hanlumi’ (Cold dew honey), ‘Huayumi’ (Flower pure honey) and ‘Baihua’ (White flower). These traditional varieties are widely used in Chinese peach production and have generated tremendous benefit to both peach growers and the local agricultural economy. Second, the germplasm resources have been used as breeding materials in conventional breeding programmes for cultivar improvement. For example, ‘Shanghaishuimi’ (Shanghai melting honey) has played an essential role in newly released cultivars both domestically and in foreign countries. In fact, many new cultivars are derived from ‘Shanghaishuimi’, such as ‘Okubo’, ‘Hakuho’, ‘Yuhualu’ and ‘Zhaohui’. Meanwhile, new introduced nectarines and their pollens have been used for hybridization with traditional Chinese varieties, resulting in a number of new Chinese nectarine varieties. This has greatly improved the nectarine varieties


available and expanded nectarine production in China. Third, progress has been made for selection of pest-resistant genotypes that have proved very useful in breeding programmes. The results of germplasm evaluation have provided valuable resistance genetic materials that have been directly or indirectly used in both conventional breeding and new genetic engineering programmes. This includes ‘Gansu Tao-1’ (P. kansuensis Rehd.) and ‘Shouxing Tao-1’ (dwarf peach, P. persica var. densa Makino) with proven root-knot nematode resistance.

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Main peach cultivars, peach production and growing regions in China

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Common (white flesh, melting) peach (P. persica Sieb et Zucc.): ‘Chunlei’ (Spring

Common peach: ‘Baixianglu’ (White fragment dew), ‘Yuhualu’ (Rain flower dew), ‘Yulu’ (Pure dew), ‘Yinhualu’ (Silver flower dew), ‘Beinong-2’ (Beijing Agricultural University – 2), ‘Zhaoxiang’ (Morning glow), ‘Xianghui-1’ (Glow ray-1), ‘Beinong Zaoyan’ (Beijing Agricultural University – Early beauty), ‘Sunagawase’ (Japanese cultivar), ‘Kurakato’ (Japanese cultivar). Yellow-fleshed peach: ‘Flavorlate’, ‘Fertilia Morettini’. Flat peach: ‘Zaokuimitao’ (Early chief flat peach), ‘Zaohuangpantao’ (Early yellow flat peach), ‘Wuyuexuanbiangang’ (May fresh flat peach), ‘Zaolupantao’ (Early dew flat peach). Nectarine: ‘Armking’, ‘Ruiguang-2’ (Lucky ray-2), ‘Ruiguang-3’ (Lucky ray-3), ‘Yanguang’ (Beauty ray).

Mid-season cultivars (91–120 days from full bloom to harvest) ●

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Very early cultivars (less than 65 days from full bloom to harvest) ●

bud), ‘Chunhua’ (Spring flower), ‘Zaoxialu’ (Early morning glow dew), ‘Huiyulu’ (Sunshine rain dew). Flat peach (P. persica f. compressa (Loud.) Rehd.): ‘Zaoshoumi’ (Early big honey), ‘Zaolupantao’ (Early dew flat peach). Nectarine: ‘Shuguang’ (Dawn), ‘Huaguang’ (China glory). Early cultivars (66–90 days from full bloom to harvest)

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A great number of peach cultivars have been developed in China with many different fruit characteristics, adaptability and market values (Wang, 1990; Wang and Zhuang, 2001). Consequently, the cultivars in Chinese peach production vary in different geographic regions and even in different provinces. The China Fruit Plant Monograph – Peach Flora (Wang and Zhuang, 2001) registers 495 cultivars with detailed information about cultivar characteristics and production. This resulted from an extensive evaluation of more than 1000 germplasm accessions conducted by the two main national peach germplasm repositories at Beijing and Zhengzhou. Below, we briefly list the main high-performance cultivars widely used in current Chinese peach production by their ripening date (Wang, 1990; Liu et al., 1999; Guo et al., 2000; Zhu et al., 2000; Wang and Zhuang, 2001). Although many varieties have been selected and developed in China and are used in current peach production, including melting peach, nectarines, flat peach and ornamental peach, the majority of the Chinese cultivars are whitefleshed and melting type, accounting for more than 80% of the total cultivars in current Chinese peach production (Zhu et al., 2003).

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Common peach: ‘Zhaohui’ (Morning sunshine), ‘Baifeng-2’ (White phoenix-2), ‘Zaoxiangyu’ (Early fragment jade), ‘Datuanmilu’ (Big honey dew), ‘Japan-89’. Yellow-fleshed peach: ‘NJC88’, ‘Cullinan’, ‘Lianhuang’ (Even yellow), ‘Chengxiang’ (Orange fragment), ‘Myoujou’, ‘Redhaven’ (USA), ‘Babygold-5’, ‘Babygold-6’. Flat peach: ‘Sahuahongpantao’ (Splash flower red flat), ‘Baimangpantao’ (White awn flat), ‘Changshengpantao’ (Longevity flat), ‘Fenghuapantao’ (Fenghua flat), ‘Chenpupantao’ (Chenpu flat), ‘Yulupantao’ (Pure dew flat). Nectarine: ‘Zhongyoupantao’ (Mid nectarine flat), ‘Zaohongzhu’ (Early red bead).

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Late-season cultivars (121–150 days from full bloom to harvest) ●

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Common peach: ‘Baihua’ (White flower), ‘Xinbaihua’ (New white flower), ‘Shenzhou’ (Shenzhou white honey), ‘Shenzhouhongmi’ (Shenzhou red honey), ‘Wanshuomi’ (Late big honey), ‘Feichengtao’ (Feicheng peach), ‘Jingmi’ (Beijing honey), ‘Jingyu’ (Beijing jade), ‘Longhuashuimi’ (Longhua melting honey), ‘Early red-2’. Yellow-fleshed peach: ‘Elberta’ (USA), ‘Fillips’, ‘Jincheng’ (Golden orange), ‘Jinxiu’ (Splendid), ‘Long 1-2-4’ (Dragon 1-2-4), ‘Xizhuang-1’ (West village – 1). Flat peach: ‘Huangroupantao’ (Yellow flesh flat), ‘Jiaqingpantao’ (Jiaqing flat), ‘Lihepantao’ (freestone flat). Very late season (more than 150 days from full bloom to harvest)

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Common peach: ‘Dunhuadongtao’ (Dunhuang winter peach), ‘Qingzhoubaipimitao’ (Qingzhou white skin honey peach), ‘Yexiandongtao’ (Yexian winter peach), ‘Zhonghuashoutao’ (China longevity peach).

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Yellow-fleshed peach: ‘Bositao’ (Persian peach). Nectarine: ‘Hongliguang’ (Red plum shine). Peach production

The total land area devoted to peaches and nectarines in China has seen a more than fourfold expansion during the period 1984– 2006 (141,351 to 652,700 ha, respectively) (Fig. 2.3). More than 45% of the total land area devoted to peaches in the world is in China. Moreover, the total production (tonnes) has followed a similar increase. By 1993, China produced more peaches than any other country in the world (Fig. 2.4). Each year since then China’s production has increased, so that, by 2006, China produced 7.5 million t. This represented 44% of the total supply. The top five producing countries in 2006 were China, Italy, Spain, the USA and Greece, producing 44%, 10%, 7%, 5% and 5% of the world total, respectively. For the last 30 years, average yield (kg/ha) has been less in China than in the other top producing countries (Fig. 2.5). However, since 1990, Chinese average yield has increased each year such that in 2006 it

700,000 650,000 600,000 550,000

Total area (ha)

500,000 450,000 China Greece Italy Spain USA

400,000 350,000 300,000 250,000 200,000 150,000 100,000 50,000

19

6 19 1 6 19 3 65 19 6 19 7 6 19 9 71 19 7 19 3 75 19 7 19 7 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 89 19 9 19 1 9 19 3 9 19 5 9 19 7 99 20 0 20 1 0 20 3 05

0 Year Fig. 2.3. Total peach and nectarine area (hectares) in the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)


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8,000,000 7,000,000

Total production (t)

6,000,000 5,000,000 China Greece Italy Spain USA

4,000,000 3,000,000 2,000,000 1,000,000

19

6 19 1 6 19 3 6 19 5 6 19 7 69 19 7 19 1 73 19 7 19 5 7 19 7 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 8 19 9 9 19 1 9 19 3 9 19 5 9 19 7 9 20 9 0 20 1 0 20 3 05

0 Year Fig. 2.4. Total peach and nectarine production (tonnes) of the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)

24,000 22,000 20,000 Average yield (kg/ha)

18,000 16,000 14,000

China Greece Italy Spain USA

12,000 10,000 8,000 6,000 4,000 2,000 19 6 19 1 63 19 6 19 5 67 19 6 19 9 7 19 1 73 19 7 19 5 77 19 7 19 9 8 19 1 8 19 3 8 19 5 8 19 7 8 19 9 91 19 9 19 3 9 19 5 97 19 9 20 9 0 20 1 03 20 05

0

Year Fig. 2.5. Average peach and nectarine yield (kilograms per hectare) in the top five producing countries during the period 1961–2006. (Source: http://faostat.fao.org, accessed August 2007.)

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was just slightly less than the USA (11,506 versus 12,731 kg/ha, respectively). The five top peach-producing provinces are Shangdong, Hebei, Henan, Hubei and Jiangsu (Wang, 2003). With current changes in the agricultural industry in China, peach acreage seems to be increasing in Sichuan and Hunan provinces where citrus was overproduced. The same trend is also occurring in Yunnan, Guizhou, Fujian, Jiangxi and Guangxi provinces where peach production is developing in higher elevation areas. In addition, peach greenhouse production and highdensity cultivation have recently emerged in limited areas of northern China. Peach-growing regions The natural range of wild peach is spread widely over much of China. However, commercial peach production is limited within the latitude range 25–45°N (Fig. 2.2/Plate 26). It is largely concentrated in northern, central to eastern and north-western China. In general, peach production in China can be divided into seven regions based on regional climate and ecological differences (Wang and Zhuang, 2001). Peach cultivars in these main production regions are divided into regional groups that are significantly different from one another. 1. North-west drought peach region includes Xinjiang and Ningxia autonomous region, Shaanxi and Gansu provinces. 2. Northern China plain region, the most important traditional and current peach production area in China. The northernmost boundary region corresponds to the Qinling Mountains and the Huai He River, including Beijing, Tianjing, Hebei province, and southern Liaoning, Shangdong, Shanxi, most of Henan, Jiangsu and northern Anhui provinces. 3. Changjiang River humid region, having a large area in central and eastern China, including southern Jiangsu, Zhejiang, Shanghai, southern Anhui, Jiangxi and Hubei and both Chengdu and Hanzhong plain areas. 4. Yunnan–Guizhou high plateau cold region, a small-restricted area including Yunnan, Guizhou and south-west Sichuan provinces. 5. Qinghai–Tibet plateau cold region, a limited area in the Tibet autonomous region, most of Qinghai and western Sichuan provinces.

6. North-eastern China cold region, this is the northernmost region of Chinese peach production, further than 41°N latitude, including Jilin and part of Heilongjiang provinces. 7. Southern China subtropical region, with south limit at 23°N latitude, including a large area to the south side of the Changjiang River of Fujian, Jiangxi, southern Hunan, north Guangdong, north Guangxi and Taiwan provinces. The first five regions are suitable peach production regions, while the last two are marginal regions, as shown in Fig. 2.2/Plate 26.

Rapid development of greenhouse production Protected cultivation of peach was successful as early as 1995 in Shandong Agricultural University (Gao et al., 2004) (Fig. 2.6/Plate 27). Greenhouse cultivation of peach has greatly extended the peach marketing season in China. Very early peach cultivars with low chilling requirement and late- or very lateseason cultivars have been promoted for the extreme early and late seasons, respectively, with fivefold higher market price than regular orchard-produced peaches. A systematic greenhouse cultivation technique has been developed, including applying plant growth regulation chemicals, reducing the size of foliage, summer pruning, girdling in the autumn, artificial application of drought stress, root pruning, and use of dwarfing rootstocks and dwarfing or semi-dwarfing cultivars. The microclimate in the greenhouse is adjusted to maximize peach production by controlling light, water, temperature, humidity and CO2:O2 ratio. In addition to applying extra artificial illumination, films with better transparency have been used for covering materials, and reflective films have been used on the ground and in the air for regulating light. Ripening stimulation is usually regulated by controlling temperature during bloom time between 5°C (night) and 22°C (day) and during fruit ripening at 25–30°C, which accelerates the ripening by 10 to 50 days. Large differences between night temperature and day temperature can improve the fruit quality. Delaying ripening is more


Fig. 2.6.

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Modern greenhouse peach production.

often practised in the northern areas. Improved insulation in greenhouses plus the frozen ground of the semi-ground greenhouses in northern China can be effective to hold a low temperature (< 7°C) in the greenhouse for 50 days during spring, when temperature is rising in March to May. This can effectively delay bud break in the spring and prolong fruit ripening for 10–30 days. The humidity and water content in the soil are usually regulated according to the growing season by irrigation. Other techniques are also used in the greenhouse, which include breaking dormancy with chemicals (hydrogen cyanamide) and applying different types of fertilizers based on the cultivars and growth season. Typical spacing in the greenhouse is 1 m × 2 m. This high planting density usually requires a special summer pruning method called PCR pruning (postharvest canopy removal) for controlling tree size. Trees before PCR are shown in Fig. 2.7/Plate 28. The method includes pruning off all current shoots as soon as fruits are harvested, followed by several summer tippings of new growing shoots for enhancing flower bud formation. Trees after

PCR are shown in Fig. 2.8/Plate 29. Foliar disease control could be a problem due to high humidity in the greenhouse production system, but greenhouse management such as ventilation and irrigation controls usually regulates humidity. The greenhouse peach production system usually remains productive for about 10 years. Intercropping systems for greenhouse peach cultivation are also being developed for maximizing the output of greenhouse productivity, such as strawberry intercropped between rows in a peach greenhouse. Currently, greenhouse peach production has reached about 14,000 ha (Li et al., 1995; Wang et al., 1995; Zhu and Wang 1997; Wang and Niu, 1998; Zhang and Yu, 2002). Peach postharvesting, processing and marketing in China Nearly all fresh peaches produced in China are marketed within the country. Marketing is as for all other fresh fruits and vegetables: farms or farming cooperatives send peaches to distribution centres (large trading centres organized

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Fig. 2.7.

Modern greenhouse peach production before postharvest canopy removal.

Fig. 2.8.

Modern greenhouse peach production after postharvest canopy removal.


by local governments), and from there the fruit are sent to fruit stores or wholesale centres in cities. Most peach production for local fresh markets requires little packing. For distant provincial markets, packing and transportation are necessary. Fruits are usually harvested before completely ripe (70–80% ripe) and packed in cardboard boxes (50 cm × 40 cm × 20 cm; about 10 kg of fruit per box) for storage and shipping. For prolonged supplies to the markets several storage techniques are usually used, mostly by cold storage, although controlled-atmosphere storage and low-pressure storage are used to a certain extent (Du et al., 2000). Cold storage usually applies 0–1°C temperature and 85–90% relative humidity, while controlled-atmosphere storage is created with 0–1°C temperature, 5% CO2 and 1–3% O2. The processed peach products in China are mostly canned, dry fruit and sliced dry products. Recently a new series of processed products has been developed with advances of modern industrial technology, including peach juice, peach tea drinks, beer, fruit jelly and peach candies (Zheng, 1995; Zheng et al., 2001). Approximately 80% of Chinese peach production is for the domestic fresh market. Small quantities of fresh peach, mostly whitefleshed melting peach, have been exported to South-east Asian countries since the mid1950s. There is a trend for increased fresh peach exports to neighbouring countries in recent years. Substantial amounts of processed products are also exported to European and American markets (Wang and Zhuang, 2001). Problems faced by the Chinese peach industry Although peach production has become an important rapidly developing industry, the lack of overall industry organization and long-term strategic planning presents barriers for future profitability (Jiang, 2000; Zhu et al., 2003). Some of the problems that need to be overcome include the following. Cultivars in production For a healthy industry, China needs a balanced proportion of different ripening peaches for a

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prolonged market supply. Particularly, the overproduced early-season peaches have greatly hampered industry development for market supply. Also, an unbalanced ratio of the white-fleshed melting peach does not meet consumer demand for a diversity of peach fruit types (Chen and Liu, 1999; Wang, 2000). Orchard management Poor orchard management is responsible for low yields per hectare, and poor fruit quality. A large percentage of peach orchards might be currently operated in extensive (low-care) cultivation. For example, high-density orchards without appropriate canopy management have caused production to decline rapidly and shortened peach tree life. Driven by short-term profit return, large-dose application of chemical fertilizers without or with less organic manures has overridden recommended management practices of balanced fertilization based on orchard age, yields, soil types and climate difference. Under these orchard practices most good cultivars cannot reach their highest yields and quality for marketing (Chen, 2002; Wang, 2000). Postharvest issues Lack of postharvesting facilities and expenses associated with handling fruit have hampered quality control (Du et al., 2000; Zhao and Chen, 2004). Protocols for peach cleaning, sorting and packing have not been well developed and are necessary for a well-regulated marketing system. Also, a lack of storage facilities and poor coordination between storage and transportation systems have caused tremendous losses during storage and transportation in some high-yielding years and reduced profit returns to peach farmers (Zhao and Chen, 2004). A well-organized provincial or regional marketing system is urgently needed. Small family farms Most Chinese peach production is on familybased small farms. This small-scale and locally operated production and marketing is probably responsible for the poor coordination of

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orchard production, postharvest handling and storage and shipping (Zhu et al., 2003). Consequently, it is difficult to standardize the production protocols and regulate quality controls. The current system must change, or the Chinese peach industry will remain less competitive within the world markets.

purposes to enhance the applications of unique Chinese peach resources (Wang and Zhuang, 2001). These new strategic goals will contribute greatly to new peach cultivar improvement and benefit the world peach industry.

Applied research and extension education

Chinese peach production will be readjusted according to market needs and new cultivar releases will be accelerated in the future. Based on peach production zones in China, the peach cultivars used in the different peach-growing regions will be more marketoriented and readjusted to market changes. For a prolonged market supply, the peach cultivars in different ripening dates may be structured as the ratio of 5:35:30:25:5 for very early cultivars (151 days after full bloom), respectively (Zhu et al., 2003). The peach market tends to have greater demand for early cultivars with larger fruit size and good flavour; for mid–late cultivars with larger size, good appearance and storage quality; and for very late cultivars with medium size, no fruit cracking, good appearance and stress tolerance (Jiang, 2000). New peach cultivar development will focus on more novel characteristics, such as high content of carotene and flesh browning tolerance for yellow-fleshed cultivars; new nectarines with wide adaptability, larger size, high fruit quality and light red or goldencoloured skin; and new flat peach cultivars with larger size, good appearance and rich flavour and aroma, and less fruit cracking. New novel cultivars will be promoted to develop niche markets. New breeding programmes for flat peach cultivars will have a greater emphasis on dwarf or semi-dwarf and compact tree forms for high-density plantings and ornamental flower types. Low-chilling genetic resources of both Chinese and foreign origin will be used to develop

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