Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing 9781774911105, 9781774911099, 9781003305033, 9835502897

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TROPICAL AND SUBTROPICAL

FRUIT CROPS

Production, Processing, and Marketing

Innovations in Horticultural Science

TROPICAL AND

SUBTROPICAL FRUIT CROPS

Production, Processing, and Marketing

Edited by Debashis Mandal, PhD

Ursula Wermund, PhD

Lop Phavaphutanon, PhD

Regina Cronje, MSc

First edition published 2023 Apple Academic Press Inc. 1265 Goldenrod Circle, NE, Palm Bay, FL 32905 USA 760 Laurentian Drive, Unit 19, Burlington, ON L7N 0A4, CANADA

CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 USA 4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN UK

© 2023 by Apple Academic Press, Inc. Apple Academic Press exclusively co-publishes with CRC Press, an imprint of Taylor & Francis Group, LLC Reasonable efforts have been made to publish reliable data and information, but the authors, editors, and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors, editors, and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged, please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, access www.copyright.com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. For works that are not available on CCC please contact [email protected] Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe. Library and Archives Canada Cataloguing in Publication Title: Tropical and subtropical fruit crops : production, processing, and marketing / edited by Debashis Mandal, PhD, Ursula Wermund, PhD, Lop Phavaphutanon, PhD, Regina Cronje, MSc. Names: Mandal, Debashis, editor. | Wermund, Ursula, editor. | Phavaphutanon, Lop, editor. | Cronje, R. (Regina), editor. Series: Innovations in horticultural science. Description: First edition. | Series statement: Innovations in horticultural science | Includes bibliographical references and index. Identifiers: Canadiana (print) 20220479348 | Canadiana (ebook) 20220479429 | ISBN 9781774911105 (hardcover) | ISBN 9781774911099 (softcover) | ISBN 9781003305033 (ebook) Subjects: LCSH: Fruit. | LCSH: Fruit—Processing. | LCSH: Fruit—Marketing. Classification: LCC SB354.8 .T76 2023 | DDC 634—dc23 Library of Congress Cataloging-in-Publication Data

CIP data on file with US Library of Congress

ISBN: 978-1-77491-110-5 (hbk) ISBN: 978-1-77491-109-9 (pbk) ISBN: 978-1-00330-503-3 (ebk)

INNOVATIONS IN HORTICULTURAL SCIENCE

Editor-in-Chief: Dr. Mohammed Wasim Siddiqui, Assistant Professor-cum- Scientist Bihar Agricultural University | www.bausabour.ac.in Department of Food Science and Post-Harvest Technology Sabour | Bhagalpur | Bihar | P. O. Box 813210 | INDIA Contacts: (91) 9835502897 Email: [email protected] | [email protected] The horticulture sector is considered as the most dynamic and sustainable segment of agriculture all over the world. It covers pre- and postharvest management of a wide spectrum of crops, including fruits and nuts, vegetables (including potatoes), flowering and aromatic plants, tuber crops, mushrooms, spices, plantation crops, edible bamboos etc. Shifting food pattern in wake of increasing income and health awareness of the populace has transformed horticulture into a vibrant commercial venture for the farming community all over the world. It is a well-established fact that horticulture is one of the best options for improving the productivity of land, ensuring nutritional security for mankind and for sustaining the livelihood of the farming community worldwide. The world’s populace is projected to be 9 billion by the year 2030, and the largest increase will be confined to the developing countries, where chronic food shortages and malnutrition already persist. This projected increase of population will certainly reduce the per capita availability of natural resources and may hinder the equilibrium and sustainability of agricultural systems due to overexploitation of natural resources, which will ultimately lead to more poverty, starvation, malnutrition, and higher food prices. The judicious utilization of natural resources is thus needed and must be addressed immediately. Climate change is emerging as a major threat to the agriculture throughout the world as well. Surface temperatures of the earth have risen significantly over the past century, and the impact is most significant on agriculture. The rise in temperature enhances the rate of respiration, reduces cropping periods, advances ripening, and hastens crop maturity, which adversely affects crop productivity. Several climatic extremes such as droughts, floods, tropical cyclones, heavy precipitation events, hot extremes, and heat waves cause a negative impact on agriculture and are mainly caused and triggered by climate change.

vi

Innovations in Horticultural Science

In order to optimize the use of resources, hi-tech interventions like precision farming, which comprises temporal and spatial management of resources in horticulture, is essentially required. Infusion of technology for an efficient utilization of resources is intended for deriving higher crop productivity per unit of inputs. This would be possible only through deployment of modern hi-tech applications and precision farming methods. For improvement in crop production and returns to farmers, these technologies have to be widely spread and adopted. Considering the above-mentioned challenges of horticulturist and their expected role in ensuring food and nutritional security to mankind, a compilation of hi-tech cultivation techniques and postharvest management of horticultural crops is needed. This book series, Innovations in Horticultural Science, is designed to address the need for advance knowledge for horticulture researchers and students. Moreover, the major advancements and developments in this subject area to be covered in this series would be beneficial to mankind. Topics of interest include: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

Importance of horticultural crops for livelihood Dynamics in sustainable horticulture production Precision horticulture for sustainability Protected horticulture for sustainability Classification of fruit, vegetables, flowers, and other horticultural crops Nursery and orchard management Propagation of horticultural crops Rootstocks in fruit and vegetable production Growth and development of horticultural crops Horticultural plant physiology Role of plant growth regulator in horticultural production Nutrient and irrigation management Fertigation in fruit and vegetables crops High-density planting of fruit crops Training and pruning of plants Pollination management in horticultural crops Organic crop production Pest management dynamics for sustainable horticulture Physiological disorders and their management Biotic and abiotic stress management of fruit crops Postharvest management of horticultural crops Marketing strategies for horticultural crops Climate change and sustainable horticulture Molecular markers in horticultural science Conventional and modern breeding approaches for quality improvement Mushroom, bamboo, spices, medicinal, and plantation crop production

BOOKS IN THE SERIES

• Spices: Agrotechniques for Quality Produce Amit Baran Sharangi, PhD, S. Datta, PhD, and Prahlad Deb, PhD • Sustainable Horticulture, Volume 1: Diversity, Production, and Crop Improvement Editors: Debashis Mandal, PhD, Amritesh C. Shukla, PhD, and Mohammed Wasim Siddiqui, PhD • Sustainable Horticulture, Volume 2: Food, Health, and Nutrition Editors: Debashis Mandal, PhD, Amritesh C. Shukla, PhD, and Mohammed Wasim Siddiqui, PhD • Underexploited Spice Crops: Present Status, Agrotechnology, and Future Research Directions Amit Baran Sharangi, PhD, Pemba H. Bhutia, Akkabathula Chandini Raj, and Majjiga Sreenivas • The Vegetable Pathosystem: Ecology, Disease Mechanism, and Management Editors: Mohammad Ansar, PhD, and Abhijeet Ghatak, PhD • Advances in Pest Management in Commercial Flowers Editors: Suprakash Pal, PhD, and Akshay Kumar Chakravarthy, PhD • Diseases of Fruits and Vegetable Crops: Recent Management Approaches Editors: Gireesh Chand, PhD, Md. Nadeem Akhtar, and Santosh Kumar • Management of Insect Pests in Vegetable Crops: Concepts and Approaches Editors: Ramanuj Vishwakarma, PhD, and Ranjeet Kumar, PhD • Temperate Fruits: Production, Processing, and Marketing Editors: Debashis Mandal, PhD, Ursula Wermund, PhD, Lop Phavaphutanon, PhD, and Regina Cronje • Diseases of Horticultural Crops: Diagnosis and Management, Volume 1: Fruit Crops Editors: J. N. Srivastava, PhD, and A. K. Singh, PhD • Diseases of Horticultural Crops: Diagnosis and Management, Volume 2: Vegetable Crops Editors: J. N. Srivastava, PhD, and A. K. Singh, PhD

viii

Books in the Series

• Diseases of of Horticultural Crops: Diagnosis and Management, Volume 3: Ornamental Plants and Spice Crops Editors: J. N. Srivastava, PhD, and A. K. Singh, PhD • Diseases of Horticultural Crops: Diagnosis and Management, Volume 4: Important Plantation Crops, Medicinal Crops, and Mushrooms Editors: J. N. Srivastava, PhD, and A. K. Singh, PhD • Biotic Stress Management in Tomato Editors: Shashank Shekhar Solankey, PhD, and Md. Shamim, PhD • Medicinal Plants: Bioprospecting and Pharmacognosy Editors: Amit Baran Sharangi, PhD, and K. V. Peter, PhD • Tropical and Subtropical Fruit Crops Editors: Debashis Mandal, PhD, Ursula Wermund, PhD, Lop Phavaphutanon, PhD, and Regina Cronje

ABOUT THE EDITORS

Debashis Mandal, PhD Assistant Professor, Department of Horticulture, Aromatic & Medicinal Plants, Mizoram University, Aizawl, Mizoram, India Debashis Mandal, PhD, is Assistant Professor in the Department of Horti­ culture, Aromatic & Medicinal Plants at Mizoram University, Aizawl, Mizoram, India. He is an academician and research fellow working in sustainable hill farming for the past 12 years. He previously worked as an assistant professor at Sikkim University, India, and has published over 60 research papers and book chapters in reputed journals and books. He has also published books with Apple Academic Press, American Academic Press, and Lambert Academic Publishing. He is also working as a member of Workgroup Lychee, Longan and other Sapindaceae Fruits of the Inter­ national Society for Horticultural Science (ISHS), Belgium, and is also a member in ISHS sections on tropical and subtropical fruits, organic horticulture, and the Commission on Quality And Postharvest Horticulture. Currently, he is working as an Assistant Managing Editor for the Inter­ national Journal of Bio Resources & Stress Management (IJBSM) and as an editorial board member of the Bulletin Agroteknologi, Research on Crops, Crop Research, Journal of Postharvest Technology, Senhri Journal of Multidisciplinary Studies, etc. Dr. Mandal is also an editorial advisor in Horticulture Science to Cambridge Scholars Publishing (UK) and regular reviewer of journals including Fruits, HortScience, ActaPhysiologica Plantarum, African Journal of Agri. Research, Journal of Food Quality, etc. Further, he is a consultant horticulturist in the Department of Horticul­ ture & Agriculture (Research & Extension), Govt. of Mizoram, India, and Himadri Specialty Chemicals Ltd., and is also handling externally funded research projects. He was convener for the International Symposium on Sustainable Horticulture, 2016, India, and co-convener for the Interna­ tional Conference of Bio-Resource and Stress Management, 2017, Jaipur, India. In addition, he was Session Moderator and Keynote Speaker at the ISHS Symposium on Litchi, India, in 2016; on postharvest technology in Vietnam, 2014 and at South Korea, 2017; and AFSA Conference in 2018, Cambodia. He is recipient of a Best Editor Award (2017) from IJBSM,

x

About the Editors

Young Achiever Award (2019) from SADHNA, Best Researcher Award (2020) by Scifax, and Young Scientist Award (2020) from the Society of Tropical Agriculture. He has visited countries including Thailand, China, Nepal, Bhutan, Vietnam, South Korea, South Africa, and Cambodia for professional meetings, seminars, and symposia. His thrust areas of research are organic horticulture, pomology, postharvest technology, plant nutrition, and micro-irrigation. Dr. Mandal did his PhD from BCKV, India, and was a postdoctoral project scientist in IIT, Kharagpur. Ursula Wermund, PhD Project Manager and R&D Coordinator Greenyard Fresh - Greenyard Fresh Trade International (UNIVEG) GmbH Ursula Wermund, PhD, is Project Manager and R&D Coordinator at Greenyard Fresh of Greenyard Fresh Trade International (UNIVEG) GmbH, Bremen, Germany. She has marked experience in professionalcorporate management, particularly in line with postharvest handling and marketing of fresh fruits and vegetables. She teaches on these subjects as well. She received her doctoral degree in Agricultural Science from Cranfield University, UK, and started her career as a research assistant at Writtle College, University of Essex, Chelmsford, UK. Later, she joined the prestigious Imperial College, Wye, UK, and became the Head of the Post-Harvest Group. During this period, she was actively associated with teaching and research related to temperate fruit production and postharvest management. Subsequently, she started her corporate assignment as head of quality management in Petter Vetter Group, GmbH, Kehl, Germany. Currently, she is a project manager and R&D coordinator for UNIVEG Group (presently known as Greenyard), Bremen, Germany. Her 13 years of corporate affairs led to her dealing with quality assurance and manage­ ment of Surinamese banana, Madagascar litchi, Italian and Turkish grapes, and Kenyan French bean, etc., in coordination with German and European Fruit Trading Association and Food Safety Working Group. She added thermal pest control and pesticide residue analysis from her experience at working with UNIVEG. She has published 14 research papers in reputed international journals in addition to participating in 11 international meet­ ings, conferences, and symposiums in different foreign countries. Her key areas of work in horticulture are postharvest technology and packaging and marketing of fruits and vegetables.

About the Editors

xi

Lop Phavaphutanon, PhD Deputy Head and Chief of the Tropical Fruit Research and Development Center, Department of Horticulture, Faculty of Agriculture at Kamphaeng Sean, Kasetsart University, Thailand Lop Phavaphutanon, PhD, is currently Deputy Head and Chief of the Tropical Fruit Research and Development Center, Department of Horticulture, Faculty of Agriculture at Kamphaeng Sean, Kasetsart University, Kamphaeng Sean Campus, Thailand. He has 30 years of teaching experience at Kasetsart University, Thailand, where he received his MSc. He has published more than 30 research papers, two book chapters, and 24 seminar papers during his active research career. Currently he is handling three research projects related to aromatic coconut and pummelo fruit. He teaches courses on principles of horticulture, physiology of horticultural crops, tropical fruits, orchard management, nutrition of horticultural crops, and research methods in horticultural sciences. He received his doctoral degree from Texas A&M University, USA, and has worked on many tropical and subtropical fruits of Thailand. Regina Cronje, MSc Horticulturist, Agricultural Research Council, Institute for Tropical and Subtropical Crops, Nelspruit, South Africa Regina Cronje, MSc, is a Horticulturist with the Agricultural Research Council of the Institute for Tropical and Subtropical Crops, Nelspruit, South Africa, for the past 13 years. She is actively associated with research of crop production technology of subtropical fruits and is currently focused on litchi and mandarin. She is serving on the Board of Directors of the South African Litchi Growers’ Association and is an active member of the South African Society for Horticultural Science and the International Society for Horti­ cultural Science. In addition, she is reviewer of reputed journals, including HortScience and the Agricultural Science Journal. She has published over 50 research papers and 15 book chapters and was chief editor for book volume published as Acta Horticulture (Proceedings of the 4th International Symposium on Lychee, Longan and Other Spaindaceae Fruits). In addition, she was the recipient of the Lindsey Milne Industry Award for outstanding contribution to the South African Litchi Industry. She earned her MSc in Crop Science at the University of Hohenheim, Stuttgart, Germany.

CONTENTS

Contributors............................................................................................................ xv

Abbreviations ......................................................................................................... xix

Preface .................................................................................................................xxiii

1.

Banana .............................................................................................................1

Sayan Sau, Panchaal Bhattacharjee, Prasenjit Kundu, and Debashis Mandal

2.

Citrus..............................................................................................................63

Prashant Kalal, Arghya Mani, Venkata Satish Kuchi, and Debashis Mandal

3.

Durian ..........................................................................................................161

Tran Van Hau, Doan Huu Tien, Nguyen Minh Thuy, Huynh Ky,

Tran Thi Oanh Yen, Mai Van Tri, Nguyen Van Hoa, and Tran Sy Hieu

4.

Grapes ..........................................................................................................201

Maria Auxiliadora Coêlho de Lima, Patrícia Coelho de Souza Leão,

Patrícia Silva Ritschel, João Dimas Garcia Maia,

George Wellington Bastos de Melo, Jovani Zalamena,

Henrique Pessoa dos Santos, Leonardo Cury da Silva,

Maria Angélica Guimarães Barbosa, Loiva Maria Ribeiro de Mello,

Celito Crivellaro Guerra, Marco Antonio Fonseca Conceição,

José Eudes de Morais Oliveira, and Marcos Botton

5.

Guava ...........................................................................................................351

Sayan Sau, Sutanu Maji, Bikash Ghosh, and Pallab Datta

6.

Jackfruit.......................................................................................................397

M. A. Rahim

7.

Litchi ............................................................................................................419

Regina Barbara Cronje, Houbin Chen, Huicong Wang, Biyan Zhou, Zhenxian Wu, Lixian Yao, Zhouyan Hu, Wene Qi, Jidong Xian, and Debashis Mandal

8.

Mango...........................................................................................................559

Dipak Nayak, Ashok Yadav, Sunil Kumar, Noel Lalhruaitluangi, and Debashis Mandal

9.

Papaya..........................................................................................................617

O. O. Olubode, O. M. Odeyemi, and I. O. O. Aiyelaagbe

Index .....................................................................................................................701

CONTRIBUTORS

I. O. O. Aiyelaagbe

Department of Horticulture, Federal University of Agriculture, Abeokuta, Nigeria

Maria Angélica Guimarães Barbosa

Embrapa Semiárido, BR 428, Km 152, PO Box 23, Zip Code 56302-970, Petrolina, Pernambuco State, Brazil

Panchaal Bhattacharjee

Department of Horticulture, Anand Agricultural University, Anand, Gujarat 388110, India

Marcos Botton

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Houbin Chen

College of Horticulture, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

Marco Antonio Fonseca Conceição

Embrapa Uva e Vinho, Experimental Station of Tropical Viticulture, Barra Bonita, PO Box 241, Zip Code 15700-971, Jales, São Paulo State, Brazil

Regina Barbara Cronje

Horticulture Department, ARC-Tropical and Subtropical Crops, Private Bag X11208, Nelspruit 1200, South Africa; E-mail: [email protected]

Pallab Datta

Department of Fruit Science, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia 735252, West Bengal, India

Bikash Ghosh

Department of Fruit Science, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia 735252, West Bengal, India

Celito Crivellaro Guerra

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Tran Van Hau

Crop Science Department, College of Agriculture, Can Tho University, Vietnam; E-mail: [email protected]

Tran Sy Hieu

Crop Science Department, College of Agriculture, Can Tho University, Vietnam

Nguyen Van Hoa

Southern Horticultural Research Institute, Long Dinh- Chau Thanh- Tien Giang, Vietnam

Zhouyan Hu

College of Food Science, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

xvi

Contributors

Prashant Kalal

Division of Fruits and Horticultural Technology, IARI, New Delhi, Outreach PhD Programme Centre, IIHR, Bengaluru 560089, India

Venkata Satish Kuchi

MS Swaminathan School of Agriculture, CUTM, Odisha

Sunil Kumar

Division of Fruits & Horticultural Technology, Indian Agricultural Research Institute, Pusa, New Delhi, India

Prasenjit Kundu

Sasya Shyamala Krishi Vigyan Kendra, Ramakrishna Mission Vivekananda Educational and Research Institute, Arapanch, P.O. Sonarpur, Dist.-South 24 Pgs, Kolkata 700150, West Bengal, India

Huynh Ky

Crop Science Department, College of Agriculture, Can Tho University, Vietnam

Noel Lalhruaitluangi

Department of Horticulture, Aromatic & Medicinal Plants, Mizoram University, Aizawl-796004, Mizoram, India

Patrícia Coelho de Souza Leão

Embrapa Semiárido, BR 428, Km 152, PO Box 23, Zip Code 56302-970, Petrolina, Pernambuco State, Brazil

Maria Auxiliadora Coêlho de Lima

Embrapa Semiárido, BR 428, Km 152, PO Box 23, Zip Code 56302-970, Petrolina, Pernambuco State, Brazil; E-mail: [email protected]

Sutanu Maji

Department of Horticulture, Babasaheb Bhimrao Ambedkar University, Vidya-Vihar, Rae Bareli Road, Lucknow 226025, Uttar Pradesh, India

João Dimas Garcia Maia

Embrapa Uva e Vinho, Experimental Station of Tropical Viticulture, Barra Bonita, PO Box 241, Zip Code 15700-971, Jales, São Paulo State, Brazil

Debashis Mandal

Department of Horticulture, Aromatic and Medicinal Plants, School of Earth Sciences & Natural Resources Management, Mizoram University (A Central University), Aizawl 796004, Mizoram, India; E-mail: [email protected]

Arghya Mani

School of Agriculture, Lovely Professional University, Punjab, India; E-mail: [email protected]

George Wellington Bastos de Melo

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Loiva Maria Ribeiro de Mello

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Dipak Nayak

ICAR-Central Institute for Subtropical Horticulture- Regional Research Station, Malda, West Bengal, India; E-Mail: [email protected]

Contributors

xvii

O. M. Odeyemi

Department of Horticulture, Federal University of Agriculture, Abeokuta, Nigeria

José Eudes de Morais Oliveira

Embrapa Semiárido, BR 428, Km 152, PO Box 23, Zip Code 56302-970, Petrolina, Pernambuco State, Brazil

O. O. Olubode

Department of Horticulture, Federal University of Agriculture, Abeokuta, Nigeria; E-mail: [email protected]

Lop Phavaphutanon

Tropical Fruit Research and Development Center, Department of Horticulture,

Faculty of Agriculture, Kamphaeng Sean, Kasetsart University, Kamphaeng Sean Campus,

Thailand; E-mail: [email protected]

Wene Qi

College of Economics & Management, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

M. A. Rahim

Department of Horticulture, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh; E-Mail: [email protected]

Patrícia Silva Ritschel

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Henrique Pessoa dos Santos

Embrapa Uva e Vinho, Livramento Street, 515, PO Box 130, Zip Code 95701-008, Bento Gonçalves, Rio Grande do Sul State, Brazil

Sayan Sau

Purba Medinipur Krishi Vigyan Kendra, Bidhan Chandra Krishi Viswavidyalaya, Mulakhop, Dayaldasi, Purba Medinipur, West Bengal 721632, India; E mail: [email protected]

Leonardo Cury da Silva

Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul, General Osório Street, 348, Zip Code 97700-206, Bento Gonçalves, Rio Grande do Sul State, Brazil

Nguyen Minh Thuy

Crop Science Department, College of Agriculture, Can Tho University, Vietnam

Doan Huu Tien

Southern Horticultural Research Institute, Long Dinh- Chau Thanh- Tien Giang, Vietnam

Mai Van Tri

South East Horticultural Research Center, Ba Ria – Vung Tau, Vietnam

Huicong Wang

College of Horticulture, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

Ursula Wermund

Greenyard Fresh Trade International (UNIVEG) GmbH, Bremen, Germany; E-mail: [email protected]

xviii

Contributors

Zhenxian Wu

College of Horticulture, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

Jidong Xian

College of Agriculture, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

Ashok Yadav

ICAR-Central Institute for Subtropical Horticulture- Regional Research Station, Malda, West Bengal, India

Lixian Yao

College of Natural Resources and Environment, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

Tran Thi Oanh Yen

Southern Horticultural Research Institute, Long Dinh- Chau Thanh- Tien Giang, Vietnam

Jovani Zalamena

Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul, Alberto Hoffmann Street, Zip Code 91791-508, Restinga, Rio Grande do Sul State, Brazil

Biyan Zhou

College of Horticulture, South China Agricultural University, 483 Wushan Rd, Tianhe District, Guangzhou 510642, China

ABBREVIATIONS

ABA AC ACC ACO ACS AFB AFLP AI AMF AOA ARC-TSC ASM AVG BB FEI BA BAU BBTV BOPP CA CARS CAT CEC CEERI CI CND CT CTKs CVA DAP DHF DWB EMS EO

abscisic acid activated charcoal aminocyclopropane carboxylic acid aminocyclopropane carboxylic acid oxidase ACC synthase after full bloom amplified fragment length polymorphism acid invertase arbuscular mychorhizal fungi aminooxyacetic acid Agricultural Research Council’s Institute for Tropical and Subtropical Crops available soil moisture aminoethoxyvenylglycine bulk blend fertilizer benzyl adenine Bangladesh Agricultural University banana bunchy top virus biaxially orientated polypropylene controlled atmosphere China Litchi Research System catalase cation exchange capacity CSIR-Central Electronics Engineering Research Institute chilling injury compositional nutrient diagnosis continuous trench cytokinins critical value approach days after pollination Dengue Hemorrhagic Fever dry weight basis ethyl methane sulphonate essential oils

xx

EPS EST-SSR EWM FAO FB FBD FCOJ FHIA FJC FYM Gas GA GAOs GDC GDD GHPS GM GP GPS GIS GRAS GRSPaV HDP HDPE HLB HSP HWD IAA IARI IBA IFS INM IPS IQF ISSR ITS LDP LDPE LER

Abbreviations

expanded polystyrene expressed sequence tag-derived simple sequence repeat entropy weight method Food and Agriculture Organization full bloom flower bud differentiation frozen concentrated orange juice Fundacian Hondurena de Investigacion Agricola frozen juice concentrate farm yard manure gibberellins gibberellic acid galacturonic acid oligosaccharides Geneva Double Curtain growth degree days greenhouse production system grass mulch grown panicles global positioning system geographic information systems generally recognized as safe grapevine rupestris stem pitting-associated virus high-density planting high-density polyethylene huanglongbing heat shock protein hot-water-dipping indoleacetic acid Indian Agricultural Research Institute indolebutyric acid initial fruit set Integrated Nutrient Management integrated production systems individual quick freezing inter simple sequence repeat internal transcribed spacer low-density planting low-density polyethylene land equivalent ratio

Abbreviations

MA MAP MARDI MCPG MD MDP (M)DRIS MIC MOP MSL MJ NAA NAD NFC NFJC NISPRIN NO NWFP OM OMF PAA PaLCuV PAR PBZ PC PET PFD PG PGRs POs POD PP PPFD PPO PRSV PSDM PVC

xxi

modified atmosphere modified atmosphere packaging Malaysian Agricultural Research and Development Institute methylene cyclopropyl-glycine Mekong delta medium-density planting (modified) diagnosis and recommendation integrated system minimum inhibitory concentration muriate of potash mean sea level methyl jasmonate naphthalene acetic acid naphthalene acetamide nonfrozen concentrate nonfrozen juice concentrate Nigerian Stored Products Research Institute nitric oxide North West Frontier Province organic matter organo-mineral fertilizer peroxyacetic acid papaya leaf curl virus photosynthetically active radiation paclobutrazol protected cultivation polyethylene terephthalate postbloom fruit drop polygalacturonases plant growth regulators pectic oligosaccharides peroxidase polypropylene photosynthetic photon flux density polyphenol oxidase papaya ring spot virus Papaya Sex Determination Marker polyvinyl chloride

xxii

PVP QTL RAPD RCTs RFLP SBD SCAR SMP SNA SNP SOC SOP SOPP SOUR SPS SRA SRAP SS SS SSH SSR ST STD STMS STS TA TDT TSS UPD USDA-APHIS UDP VAM VOD VSP WBR XET ZEC ZRs

Abbreviations

polyvinylpyrrolidone quantitative trait loci random amplified polymorphic DNA rainwater conservation techniques restriction fragment length polymorphism soil bulk density sequence characterized amplified region Shoemaker, Mc Lean, and Pratt Method sodium naphthalene acetate single nucleotide polymorphisms soil organic carbon sulfate of potash sodium ortho-phenyl phenate suppression of uniform ripening sucrose phosphate synthase sufficiency range approach sequence-related amplified polymorphism soluble solids sucrose synthase suppressive subtraction hybridization simple-sequence repeat staggered trench short-term -duration sequence tagged microsatellite sites silver thiosulfate titratable acidity total daily temperature total soluble solids underpeel discoloration USDA Animal and Plant Health Inspection Service ultra-density planting vesicular arbuscular mycorrhiza vacuum osmotic dehydration vertical shoot positioning weed biomass rating xyloglucan endo-transglucosylase zero-energy evaporative coolant zeatin-ribosides

PREFACE

Tropical and subtropical fruits are known and appreciated for their exotic aromas, textures, and tastes as well as for their nutritional and medicinal value. These attributes and a renewed health consciousness have increased consumer demand for these fruits. Out of the hundreds of tropical and subtropical crops only some 50 are well known and even less are grown on a commercial scale. Most of the best-known ones come from the tropical and subtropical regions of Asia and America. They are important to many developing countries as a contribution toward income and as a source of nutrition. Major tropical and subtropical crops, such as citrus, banana, and mango are extensively cultivated and marketed in local and export markets. Minor tropical and subtropical crops, such as litchi, papaya, and guava, have limited consumption and trade but may have high regional importance. Despite their increasing popularity, the cultivation of tropical and subtropical fruits is limited to areas with warm temperatures and high humidity throughout most of the year. Due to their highly perishable nature, postharvest handling, transport, and storage has always been a challenge. While tropical and subtrop­ ical fruits are still mainly consumed fresh, good advances have been made in processing and value-adding in the past few decades. The commercial success of tropical and subtropical fruits worldwide has also favored the development of agro technology, sustainable crop production techniques, integrated pest management, and, in particular, postharvest technologies and handling tech­ niques. Likewise, biotechnology and molecular biology are increasingly used in breeding programs to develop varieties with improved fruit characteristics, shelf life, and the ability to withstand the adverse effects of climate change. In this regard, this book volume, Tropical and Subtropical Fruit Crops: Production, Processing and Marketing, provides comprehensive informa­ tion on the latest developments and research efforts in crop production techniques, processing, and marketing, breeding efforts, harvesting and postharvest handling, as well as pest and disease management of banana, citrus, durian, grapes, guava, jackfruit, litchi, mango, and papaya. Debashis Mandal Ursula Wermund Lop Phavaphutanon Regina Cronje

CHAPTER 1

BANANA Sayan Sau1*, Panchaal Bhattacharjee2, Prasenjit Kundu3, and Debashis Mandal4 Purba Medinipur Krishi Vigyan Kendra, Bidhan Chandra Krishi Viswavidyalaya, Mulakhop, Dayaldasi, Purba Medinipur 721632, West Bengal, India

1

Department of Horticulture, Anand Agricultural University, Anand 388110, Gujarat, India

2

Sasya Shyamala Krishi Vigyan Kendra, Ramakrishna Mission Vivekananda Educational and Research Institute, Arapanch, Sonarpur, South 24 Pgs., Kolkata 700150, West Bengal, India

3

Department of Horticulture, Aromatic and Medicinal Plants, School of Earth Sciences & Natural Resources Management, Mizoram University (A Central University), Aizawl 796004, Mizoram, India

4

Corresponding author. E-mail: [email protected]

*

ABSTRACT Banana, a member of the Musaceae family, belongs to the genus Musa, which comprises a significant variety of species and hybrids. Though there are over thousand varieties of bananas grown and consumed worldwide, the Cavendish type banana crowned the most commercialized variety tag, accounting for about 47% of global production. In 2018, global banana exports (excluding plantains) are forecast to touch a new high of 19.2 million tons due to ample growth in its supply. Bananas and plantains are the only Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing. Debashis Mandal, PhD, Ursula Wermund, PhD, Lop Phavaphutanon, PhD & Regina Cronje, MSc (Eds.) © 2023 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

2

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

known items under fruits that also constitute a staple food for millions. It is a recommended dietary supplement to lower blood pressure as it contains low salt and high potassium chloride. Bananas are a well-accepted food item in antique medicine in China, India, and ancient Persia due to its effective­ ness against obesity, peptic ulcer, infant diarrhea, celiac disease, and colitis. Banana commercially propagated through suckers and more recently for uniform yield and less disease infection plantlets developed through tissue culture are recommended. Seeds are used only in breeding program. Advanced cultivation practices such as sucker management, drip irrigation scheduling, adoption of fertigation, and bunch management lead to achieving higher productivity. Researchers over the world engage in developing new cultivars through several breeding programs like hybridization, selection, mutation to escape the devastating disease like sigatoka, BBTV, and fusarium wilt. In recent times, ripening improvement through standardized ethylene treatment and storing of banana in CA/MA storage makes it possible to store them for a longer duration and safe disposal in targeted market with minimum loss. 1.1 GENERAL INTRODUCTION Banana belongs to Musa genus a member of family Musaceae. The name Musa finds its origin to Sanskrit word “moca,” via its Arabic source, “mauz.” Banana appeared as “the tree of paradise” in Quran. Bananas were mainly derived from two wild ancestral sources: Musa acuminata and Musa balbisiana (Lehmann et al., 2002). Present day’s bananas and plan­ tains found their native in South-East Asian and western Pacific provinces (Carreel et al., 2002) are seeded, inedible, in the natural forest flora of these regions of diversity, ancestors with diploid set of chromosomes can still be traced (Robinson, 1996). At present, it is nearly ubiquitous in all tropical and subtropical climate zones of the world; it is widely cultivated as one of the important remunerative fruit crops and also serves as staple food commodity in several communities. Bananas at its ripe stage are sweet and easily digestable making them one of the preferred dessert fruits. Gowen (1988) discussed the apparent ambiguity of using the term “plantain.” As the fruits ripen, there is a process of conversion of starch to sugar which is relatively slower in cooking varieties (plantains), typical M. balbisiana characteristic. Different names are used to address banana in the various countries of the world, as discussed by Uma et al. (2011); this is given in Table 1.1.

Banana

TABLE 1.1

3

Common Names of Banana in Different Countries or in Languages.

Name

Country/ Language

Name

Country/ Language

Name

Country/ Language

banana

Japanese, Italian, Portuguese, Serbo-Croat, Hebrew

banema

Guinea

klue/klui

Thai

banane

French, German

Choui

Vietnam

mauz

Turkish, Arabic/ Persian

banaan

Dutch

Chiao

Chinese

maso/ndizi Swahili

Banan

Danish

Futo

New Caledonia pisang

Malay/Indonesian

banaani

Finnish

Futi

West Polynesia saging

Philippines

Banan

Russian/Polish hnget-pyaw

banbán

Hungarian

mpanána Greek

Burmese

usi

New Guinea

ikindu/ kitoke

East African

uch/ut

Micronesian

Kela

India

vudi

Fiji

With the progression of technologies in the late 1800s like refrigerated shipping that served as the base of the global banana trade industry, banana exhibits colonial economic nationalism and present-day neoliberal stages of growth and evolution in the world economy (Wiley, 2008). Banana gained reputation for its diversity and skill of adapting into multiple agro-climatic zones, buoyancy to changing climate, fruit yield attribute throughout the year, and large volume per unit yield. The spectrum of cultivar diversity and differential maturity trait allows its adoption and cultivation in more than 155 countries (Uma et al., 2011). 1.2 AREA AND PRODUCTION Bananas are produced and consumed worldwide, but the Cavendish variety is produced commercially most, which accounts for 47% of global share. Cavendish bananas with their dwarfing and storm-resistant structure can recover quickly from natural disasters and this helps it to attain higher yield. Production scenario depicts that 45–50 billion tons (approx) of Cavendish bananas are produced around the world. The Cavendish variety is preferred for foreign trade than other varieties because it is more resis­ tant to the effects of shipping and thus accounts for the majority of bananas

4

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

supplied to the US and European markets. Cavendish bananas are also the most popular variety grown and consumed in China and India (FAOSTAT via Bioversity). A comprehensive figure on global banana production goes untrackable as it comes from small-scale growers with marginal land holding who sell them in informal markets. Available data shows a growth of 3.2% in global production since 2000 (67 million tons) reaching a record of approx. 114 million tons in 2017. According to FAOSTAT, total area in world under banana cultivation in 2017 is 5637,508 ha with total yield of 113,918,763 t and the resulting productivity of 20.21 t/ha. The leading five countries in the world with a higher average banana production (million tons per year) during 2010–17 are India (29), China (11), Philippines (7.5), Ecuador (7), and Brazil (7), respectively (Table 1.2). India is the current top producer of banana with 30,808 (‘000 MT) total yield from acreage of 884 (‘000 Ha) (NHB Database, 2018). Overall, the global banana industry has witnessed improved sign in productivity, with the average yield per unit area shifting from around 14 t/ha (1993) to 20 t/ha in 2017. It has to be mentioned that statistics provided by the FAO do not distinguish between plantain and banana. TABLE 1.2 Production and Productivity Status of Top Banana Growing Countries in the Year 2017. Production Scenario Sl. No.

Country

Productivity Scenario Unit (million tons)

Sl. No. Country

Unit (t/ha)

India

304.77

Syrian Arab Republic

70.4927

China

225.93

Nicaragua

65.8088

Indonesia

71.63

Indonesia

60.1906

Brazil

66.75

South Africa

59.8494

Ecuador

62.82

Costa Rica

59.4772

Philippines

60.41

Turkey

54.099

Angola

43.02

Israel

52.5692

Guatemala

38.87

Puerto Rico

50.5256

Colombia

37.87

Greece

49.2222

United Republic of Tanzania

34.85

Guatemala

48.4953

Costa Rica

25.53

Spain

46.4206

Mexico

22.30

Côte d'Ivoire

46.0917

Banana

TABLE 1.2

5

(Continued)

Production Scenario Sl. No.

Productivity Scenario

Country

Unit (million tons)

Sl. No. Country

Unit (t/ha)

Viet Nam

20.45

Jordan

44.912

Rwanda

17.29

Egypt

42.8534

Papua New Guinea

12.47

Dominican Republic

42.0593

Source: FAOSTAT Database (2019).

India and China both increased their production between 2000 and 2015, nearly doubling their banana harvesting area and increasing yields by 48% and 83%, respectively. 1.3

MARKETING AND TRADE

Considering about the abundant development in provisions, worldwide exports of banana are projected at a record high of 19.2 million tons in 2018, excluding plantains. Ecuador and Philippines are the main patron or contributor in ascent of worldwide banana export market. Ecuador, the chief exporter of bananas worldwide, was expecting a 4% growth in supply to arrive at another raise of 6.7 million tons in 2018, ensued for favorable climate conditions and yield-improving innovations. Booked tax decreases under the EU-Andean arrangements in 2018, which encouraged passages to the EU market at a diminished pace of 96 EUR/t over time will profit Ecuadorian shipments. Ecuador is required to represent a volume portion of almost 40% of worldwide shipments in 2018. Analyzing India’s export market of banana during 2017 through Export Genius (An exim exchange information research firm) report, it has sorted out that however India being number one producer of banana, its export probability is moderately low because of higher homegrown utilization or domestic consumption. India trades most amount of bananas to Middle East nations in which the United Arab Emirates, Saudi Arabia, Oman, Kuwait, and Iran beat out all competitors. UAE and Oman recorded 31.58% and 19.68% share in estimation of banana imports from India, respectively.

6

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

1.4 COMPOSITION AND USES Nutrient contents of tropical fruits found in food organization tables are utilized for the appraisal of nourishing level, connecting diet to wellbeing, dietary arrangement, and food bundle naming and customer awareness. Precise information is required to anticipate dietary energy admission and under nourishment. For tropical organic products like banana, this is signifi­ cant, as they are regularly viewed as huge wellsprings of minerals, nutrients, and starches (Favier et al., 1993). Characteristic variation happens in the nutrient contents because of soil and climatic conditions, varieties grown, the phase of development at collect and physiological state when eaten. Generally, food synthesis tables for most nourishment are introduced as mean qualities, overlooking the regular natural inconstancy. It is presumably more helpful to know the scope of qualities found and the standard error or deviation. The pulp of plantain contains less water than that of banana (Table 1.3). During maturing there is transformation of starch to sugars in pulp, because of respiratory breakdown and peel color is firmly associated with the starch:sugar proportion. Starch declines from about 20–23% at harvest to 1–2% in ripe fruit. TABLE 1.3

Proximate Composition of Mature Banana and Plantain Fruit Pulp.

Nutritional Content (% Pulp Fresh Mass)

Banana

Plantain

Water (%)

71.3–75.7

64.1–66.7

Energy (kJ)

418

523

Protein

1.08–1.10

1.10–1.28

Lipid (g)

0.13

0.03

CHO (g)

22.2–26.56

31.20–33.39

Fiber (g)

0.11

0.43

Ash (g)

0.80–0.90

Minerals content (mg/100 g pulp)

P

K

Ca

Mg

Fe

S

Na

Banana

18–27

460–494

5–7

36–40

0.49

34

1

Plantain

21–32

393–440

4–14

32–35

0.54

24

1

0.87–0.90

Banana

TABLE 1.3

7

(Continued)

Vitamin content (mg/100 g pulp)

Vitamin Thiamine Riboflavin Niacin (B2) (B3) A (IU) (B1)

Pantothenic Ascorbic Acid (B5) acid (C)

Banana

88

0.044

0.045–0.07 0.69

0.26

5.1–10

Plantain

31

0.038–0.05 0.05–0.064 0.43

0.37

17.5–20

Source: Adapted from Stover and Simmonds (1987), Wenkam (1990), John and Marchal (1995).

Many African nations, Latin America, the Caribbean, and the Polynesian islands consider plantains to be a staple food, where people used to consume banana in different forms like fresh, cooked, steamed, roasted, and brewed (Pillay et al., 2002). The average global per capita consumption of banana and plantain is reported as 5.2 kg/person (Nayar, 2010), but it is signifi­ cantly much higher in tune of 239 kg/person in Uganda, 223 in Burundi, 180 in Rwanda, 141 in Gabon, and 131 in Samoa where it is revered as fruit equivalent (as per FAOSTAT Database, 2019), with a marginal incremental approach. Besides the fruits, the flower buds and inner core of the pseudostem are also used as vegetables in addition to their wide range of therapeutic uses. Bananas are also processed into puree, juice, fig, jams, canned banana slices (Thompson, 1995), and wine and beer in Africa (Olaoye et al., 2006). In India's traditional medicine, bananas are believed to be nature's secret to everlasting youth; in China and ancient Persia, banana is considered an ideal diet for obese and geriatric patients due to the low lipid and high energy values (Gasster, 1963). Bananas are low in salt and high in potas­ sium chloride, and thus it is a recommended dietary supplement to lower blood pressure. It is also effective against peptic ulcer, infant diarrhea, celiac disease, and colitis (Seelig, 1969). Banana can enhance production of hemoglobin in blood which helps anemic persons and banana being rich in tryptophan, which gets converted into serotonin in the body, helps to keep the mind relaxed. For expectant mothers, fruits are considered coolant. Being rich in fiber and pectins, banana helps to improve bowel movement. Benign amino acids that are useful for the kidney and the removal of gall bladder stone are also found in banana. Banana serves as a good source of lectins, which are sugar-binding proteins that can identify foreign invader pathogen and check their entry to the body. Banana roots also possess an antihelmintic effect (Uma et al., 2011). Banana leaves are considered hygienic dining plates and wrapping mate­ rial. Nowadays, leaf production is also considered an income source for

8

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

small-scale farmers in South India and Africa. The subterranean rhizome is used in a hybrid blend as animal feed. The banana’s pseudostem has proven to be a successful substrate for mushroom cultivation either alone or in combination with rice straw. The banana plant saps are also used as an indelible ink in the industry. Owing to optimum burst, tear, and tensile indices, banana fiber also finds its use in the pulp industry and as a base material in cottage industries for making handicrafts and for making a wide range of handicrafts, also being utilized for treatment purposes of industrial and municipal wastes (Uma et al., 2002). Banana fiber is derived from M. textilis having great tear and tensile strength that makes it extensively suitable for printing of Japanese yens and is also blended with cotton in various ratios for use in the textile industry. 1.5 ORIGIN AND DISTRIBUTION With vast diversity, utility, and spread, banana and plantain is a complex crop and addressing their origin is difficult compared to other crops. After their simultaneous and independent evolution across Asia, Polynesia, and Africa, metamorphosis of the earliest wild banana, a weedy, seeded, nonedible plant into a domesticated, parthenocarpic (nonseeded), edible tasty fruit occurred in a long evolutionary journey. Banana is one of the primitive crops to be domesticated by man mostly due to its various uses. Current forms of bananas are predicted to have originated in the Southeast Asian and Pacific West areas, where still their inedible, seeded, diploid ancestors habitat in natural forest vegetation. As a wild-seeded plant, banana must have been first recognized for purposes like fiber, roofing, and ropes. The earliest documentary evidence of banana is found in the Vedic period (approx. 1700 BCE). Buddhist sculptures of central India, stupas in Sanchi, carvings in Nalanda, and paintings in Ajantha and Ellora caves act as proofs of early cultivation of banana in human civilization. First mention of the banana in Chinese texts was done by a Chinese official in the T’ang dynasty (618–907), who wrote an Encyclopedia of Rare Things that includes the description of the banana plant. Plantains, too, have a long tradition of domestication, their entry to the continent of Africa is reported to be about 1500–2000 years ago and Phytoliths of Musa and Ensete unearthed in Cameroon are the first

Banana

9

archeological indication of a cultivated crop, dating back 3000 years in Central Africa (Mbida et al., 2000). At present dessert banana is widely cultivated in warm humid regions of Indian subcontinent, southern America, Caribbean islands, and south-eastern Asia. In case of plantains most cultivars are triploid, 73% of them are grown and eaten in West and Central Africa, and were formed from crosses between M. acuminata and M. balbisiana (Robinson, 1996). 1.6 BOTANY AND TAXONOMY The banana plant is a nonwoody tree-like enduring herb. One of the offshoots developing at the foundation of the plant called as the sucker takes over after the aerial parts of the parent plant fade away to the ground after the devel­ oping season showing its perennial character. Smaller masse of covering and spirally organized leaf sheath give a trunk the same design known as pseu­ dostem, while the “true” stem is created inside the pseudostem. The varia­ tions saw in morphological attributes is utilized to portray or characterize banana plants (Anonymous, 1996). The rhizome is an underground structure creating the roots. It is customarily categorized as a corm, and seldom as a bulb; however, the naturally right term is rhizome (Robinson and Galán, 2010). Primary roots of banana ascend from the outside of the focal chamber of rhizome though optional and tertiary roots start from the primary roots. In the transition phase from the vegetative to the reproductive stage, the straightened arch formed meristem zone gets curved and transcends the encompassing leaf bases. Bloom bracts supplant the leaves and after the arrangement of the blossom, the aeronautical or aerial stem begins its turn of events and bears the bloom and leaf upward, eventually arising at the highest point of the pseudostem (Skutch, 1932). Individual leaf shows up from the focal as well as the central point of the pseudostem as a rolled cylinder. As indicated by cultivar inclination the distal finish of the extending leaf sheath contracts into a petiole which is pretty much open. Leaf petiole formed into mid rib separates the leaf edge into two lamina parts. The upper and lower surfaces of the leaf are naturally named as adaxial and abaxial, respectively. Scale leaves are the primary rudimentary leaves created from a growing sucker. Foliage leaves are the developed one comprising of sheath, petiole, midrib, and blade, while recently emerged leaf remains rolled as a cylinder termed as “Cigar leaf.” Unfurling of moved leaf by and large requires around 7 days under good condition, yet may draw out dependent upon 15–20 days

10

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

in bad weather conditions. The white hued new leaves of banana are firmly snaked and for the most part fragile in surface. The tip augmentation of the leaf called as precursory appendage withers and tumbles off after emergence. Horizontal shoot found in close proximity to the parent plant usually created from rhizome is called sucker, synonymous to keiki (in Hawaii) and pup. Peeper is a kind of sucker which has recently arisen through the soil surface while the “Maiden sucker” is a completely full grown mature sucker having foliage leaves. Morphologically suckers are of two kinds, for example sword sucker with slender leaves and a huge rhizome and water suckers with expansive leaves and a little rhizome. Water suckers are of more fragile association with mother plant and accordingly do not form into strong successive plant. “Follower or ratoon” term indicates a sucker that is chosen for replacing the parent plant in the wake of fruiting. Botanically, the banana inflorescence is a thyrse, for example, an inflorescence wherein the main axis continuing developing yet the hori­ zontal branches with determinate development propensity or growth habit (Kirchoff, 1992). Banana inflorescence comprises of three sorts of blossoms, at basal bit female blossoms (forms into fruit parthenocarpically, i.e., without fertilization) arranged in two lines, at distal portion cluster of male blossoms (produces pollen of varying degrees of fertility) exist, and in the middle of them there is third kind of flower for example bisexual or hermaphrodite or neutral one (does not form fruit). Inflorescence is upheld by a stalk called as peduncle while the stalks upheld the individual male and female blooms that are named as rachis (Anonymous, 1996). Male blooms encased in bracts have kept themselves secure in male bud that is otherwise called chime having inclination of proceed with development even after the development of the organic product aside from some cultivar. Bunch the spellbinding term means all the fruits in general. The fruits that are arranged into hands are frequently called fingers and the quantity of hands relies on ecological condition, female bloom rate, and sorts of cultivar (Fig. 1.2). Till date the largest bunch, as per Guinness World Records, weighs around 130 kg. Linnaeus, in Species Plantarum (1753), first allotted logical terminology and scientific nomenclature to bananas by describing Musa paradisiaca L. Botanically, the whole entire cultivated bananas are grouped into the class Musa, which—along with two different genera, Musella and Ensete—are set in the family Musaceae and order Zingiberales. Cheesman (1947) built up a satisfactory and acceptable classification for the genus Musa where he assembled the species in the family Musa into four segments, namely, M. faction. “Eumusa” (M. sect. Musa), M. sect.

Banana

11

Rhodochlamys (Baker), M. sect. Australimusa, and M. sect. Callimusa. He demonstrated that “the groups have intentionally been called segments instead of subgenera trying to evade the ramifications that they are of equivalent position.” He further mentioned that his distribution may invigorate explora­ tion and recognizable proof monetarily significant undiscovered species of Musa family. Argent (1976) later depicted another Musa sect. Ingentimusa dependent on a single species, Musa ingens. With the assistance of established genomic characters the broadly acknowledged order of edible bananas was formulated by Simmonds and Shepherd (1955). They proposed the theory of banana advancement from wild and seedy ancestors, namely, Musa acuminata (2n = 2x = 22) and Musa balbisiana (2n = 2x = 22), originating from South-East Asia, following the development of series of seedless diploid, triploid, and tetraploid bananas. The subsequent genome groups were named AA, AB, AAA, AAB, ABB, AABB, AAAB, ABBB with the letters A and B addressing the commitments of M. acuminata and M. balbisiana, respectively. Ancestral types of banana and their contributing genome to build up the present genomic classifica­ tion resemble “A” genome from M. acuminata Colla, “B” genome from M. balbisiana Colla, “S” genome from M. schizocarpa, and “T” genome from Musa textilis. Certain quantities of clone developed in Philippine may have come from early hybridization between M. balbisiana and Musa textilis (T genome). Clones involving A and T genomes or even A, B, and T genomes have been recognized in Papua New Guinea (Robinson and Galán, 2010). Numerous molecular phylogenetic researches on the genus Musa showed that none of the five sections of Musa characterized by Cheesman and Argent recently dependent on morphology was recuperated as monophyletic. Just two infrageneric clades could be distinguished, which compared well to the basic chromosome numbers of n = x = 11 and n = x = 10/9/7, individu­ ally of which one clade involves species from Eumusa and Rhodochlamys segment, while the other contains species from Callimusa, Australimusa, and Ingentimusa segments (Li et al., 2010; Christelová et al., 2011). Häkkinen (2013) rebuilt Musa species into just two segments thinking about a sum of 70 species, namely, group Musa (Eumusa and Rhodochlamys) and sect. Callimusa (consisting of erstwhile Callimusa, Australimusa, and Ingenti­ musa), in view of the DNA analyses referred to above. The following 33 species are assigned to section Musa L. sect. Musa by Häkkinen (2013); species marked with an asterisk (*) were previously placed in Musa sect. Rhodochlamys.

12

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

1. Musa acuminata Colla

12. * Musa kattuvazhana

23. Musa schizocarpa

2. * Musa aurantiaca

13. Musa lanceolata

24. Musa shankarii

3. Musa balbisiana Colla

14. * Musa laterita

25. * Musa siamensis

4. Musa basjoo

15. * Musa mannii

26. Musa sikkimensis

5. Musa celebica

16. Musa nagensium

27. Musa thomsonii

6. Musa cheesmanii

17. Musa ochracea

28. Musa tomentosa

7. * Musa chunii

18. * Musa ornata

29. Musa tonkinensis

8. Musa flaviflora

19. * Musa rosea

30. * Musa velutina

9. Musa griersonii

20. * Musa rubinea

31. Musa yamiensis

10. Musa insularimontana

21. * Musa rubra

32. Musa yunnanensis

11. Musa itinerans Cheesman

22. * Musa sanguinea

33. * Musa zaifui

The following 37 species are assigned to the section Musa sect. Callimusa by Häkkinen (2013); species marked with an asterisk (*) or a plus (+) were previously placed in M. sect. Australimusa or in M. sect. Ingentimusa, respectively. 1. * Musa arfakiana

14. Musa haekkinenii

26. Musa paracoccinea

2. Musa azizii

15. Musa hirta Becc.,

27. * Musa peekelii

3. Musa barioensis

16. + Musa ingens

28. Musa sakaiana

4. Musa bauensis

17. * Musa jackeyi

29. Musa salaccensis

5. Musa beccarii

18. * Musa johnsii

30. Musa splendida

6. * Musa boman

19. * Musa juwiniana

31. * Musa textilis

7. Musa borneensis

20. Musa lawitiensis

32. * Musa troglodytarum

8. * Musa bukensis

21. Musa lokok

33. Musa tuberculata

9. Musa campestris

22. * Musa lolodensis

34. Musa violascens

10. Musa coccinea

23. Musa lutea

35. Musa viridis

12. * Musa fitzalanii

24. * Musa maclayi

36. Musa voonii

13. Musa gracilis

25. Musa monticola

37. Musa paracoccinea

Latest additions in the existing edition of banana species occurred in 2016 and 2014, respectively. Two new species, naming Musa paramjitiana sp. nov. (Musaceae) close to Musa balbisiana var. andamanica with few varying plant characters and M. indandamanensis, was described and illus­ trated, from India’s Andaman and Nicobar Islands (Singh, 2014, 2016). In 2017, it was found in a study that the newly published species of Musa, namely, M. indandamanensis and M. paramjitiana, are actually synonymized

Banana

13

under M. sabuana and M. balbisiana var. andamanica, respectively. It was further clarified from the critical study of types and specimens conducted with live samples collected from their natural habitat at the Andaman and Nicobar Islands and Northeast India (Hareesh et al., 2017). 1.7 VARIETIES AND CULTIVARS By and large for commercial aspects, bananas are classified into two types like dessert and cooking types (Table 1.5, 1.6 and Fig. 1.1). The cooking type bananas are described by starchy fruit and commonly utilized as vegetables as on unripe structure. Cultivars and landraces inside a genome are again assigned with different “Group” and “subgroups.” Wild accessions are demonstrated as “types.” Diplois are profoundly characterized by their slender pseudostems and more erect leaves, while the triploids are bigger, sturdier plants with increased fruit size. Triploid cultivars are ordered under three genomic groups namely, AAA, AAB, and ABB. Tetraploid cultivars are very few having robust pseudostem and dropping leaves, ordered under AAAA, AABB, AAAB, and ABBB genomic groups. Tetraploids are devel­ oped from fertilization of triploid egg cells by haploid pollens. The genome scoring methods depended on specific explicit of 15 char­ acters of both the ancestral species, for example, M. accuminata and M. balbisiana. These scoring methods accommodate a value of 15 (15 × 1) for wild acuminata and 75 (15 × 5) for wild balbisiana species. The scoring technique follows a score value distribution as resemblance to each character of acuminate, getting a score value of 1 while this value is 5 for each char­ acter matched with balbisiana species. The acuminata cultivar should score between 15 and 25 while unadulterated balbisiana should range from 70 to 75 and hybrids are between 26 and 69 (Table 1.4). TABLE 1.4

Genomic Group-Wise Important Banana Cultivars.

Sl. No. Genomic group

Cultivars belonging to this group

AA

Mati, Kadali, Anaikomban, Sucrier

AB

Neypoovan (safedvelchi, chinichampa, Rasagali), Adukkan

BB

Bhimkol, Attaikol

AAA

Gros Michel, Dwarf Cavendish (Singapuri, Basrai), Robusta (Harichal, Bombay Green, Giant Governor), Giant Cavendish (Shrimanti, Padarsi, Gandevi), Grand Naine, Red Banana (Agniswar, Anupam, Rathambala, Lalkela, Yeratti)

14

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

TABLE 1.4

(Continued)

Sl. No. Genomic group AAB

Poovan/Mysore (Champa, LalVelchi, Dudhsagar), Pome subgroup (Virupakshi; syn. Hill banana, Vellavazhai); Silk subgroup [(Rasthali; syn. Amruthapani, Malbhog, Martaman, Rassabale, Sonkel), Amrit Sagar, Chakarakeli]; Plantain subgroup (Zanziber, Moongli)

ABB

Bulggoe (syn; NallaNontha), Monthan (syn; Kanchkela), Pisang Awak (syn; Karpuravalli)

BBB

Saba, Cardaba

AAAA

Bodles Altafort

AAAB

FHIA-01(Gold Finger), FHIA-18, FHIA-20, FHIA-21

AABB

Pisang Awak, FHIA-03

ABBB

Klue Teparod, Swai (synthetic hybrid)

TABLE 1.5 Sl. No.

TABLE 1.6 Sl. No.

Cultivars belonging to this group

Important Cultivars of Different Countries. Country

Cultivars

Australia

Robusta, Williams, Cocos

Brazil

Robusta, Santa Catarina Silver, Brazilian

China

Dwarf Cavendish

Philippines

Common Dwarf, Lakatan

South Africa

Dwarf Cavendish, Golden Beauty

Taiwan

Giant Cavendish

Thailand

Bluggoe, Maricongo, Common Dwarf

USA

Dwarf Cavendish, Enano Gigante, Giant Cavendish, Ice Cream, Macho, Orinoco, Pisang masak hijau.

Features of Some Important Banana Varieties Grown over the World. Cultivar

Important Features

Cavendish

It is the most common cultivar in Europe, and it is consumed fresh as well as in smoothies, yogurts, and cakes. Also it is used in sweetening savory dish. It develops balanced sweetness and texture when still yellow with green tips

Creamily Sweet Reds

Red, short, delicate, and sweet fruits with a light raspberry flavor. Extra vitamin C and beta-carotene can be found in cream-colored fruits. Used as snack, in ice cream as a desert or even in savory dishes

Banana

TABLE 1.6 Sl. No.

15

(Continued) Cultivar

Important Features

Sweet Babies

Since a baby banana is only a one-third the size of a regular banana but exceptional for its immense nutritional richness. It is different from other bananas for its unique taste and texture. Baby bananas can be eaten raw or used in baby food, cakes, smoothies, and other desserts

Delicately Apple Manzanos (“Apple banana”)

Apple flavored sweet banana, lusciously different and a rich source of fiber, potassium, and vitamin C

Fabulously Fruity Prata

Most popular in Brazil. Yellow-colored bananas are somewhat square shaped with unique taste. It is best to eat it when it is brown and a little sloppy. Taste of the pulp quiet matches with kiwi fruit and citrus

Grand Naine

Globally accepted variety of Giant Cavendish subgroup with commercial significance and of premier export market. It gets vast acceptability for both dessert and processing purposes. It has a better pulp-to-peel ratio and has more market acceptability. This one is characterized by medium to tall-stemmed herb, with cylindrical stems. Each plant yields about 25 kg and it may attain a level of 32–35 kg in combination of 8–10 hands with 200–220 fruits/ bunch in the crop duration of 11–12 months. The fruit measures 15–21 cm in length and 12–13 cm in circumference

Robusta

This banana plant has a typical stature and brownblack blotches on the stem, having 8–10 hands/bunch with the weight of around 20 kg. Fruits with thick skin are 15–20 cm in length and 11–12 cm in girth

Red Banana

Synonymous as Lal Kela, Anupam, Chandrabale, Kembale, Chenkadali, Chevvazhai, Yerra Arati, and Agniswar. This common and expensive variety is grown commercially in different parts of South India. This elite banana cultivar gets its fame for its red peeled luscious flesh and distinctive taste. Robust statured plants are ranged 2.5–3.0 m in height. Fruit, pseudostem, petiole, and midrib are purplish red in color and have a good fragrance. Bunches range between 20 and 30 kg with 6–7 hands under optimum crop management conditions with 16–18 cm lengthy 70–90 robust fruits. Problem identified with this variety is its susceptibility to banana bunchy top virus (BBTV), fusarium wilt and nematodes

16

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

TABLE 1.6 Sl. No.

(Continued) Cultivar

Important Features

Poovan

This cultivar is medium statured and ranges 2.7–2.8 m in height. Characteristic green, shiny pseudostem with uneven pink–purple pigmentation makes it visibly different from other cultivars. Leaf is intermediate in habit, medium green colored with small brown–black blotches at the base of petiole. Peduncle is smooth, green and with very short hairs. Fruit borne in cluster of 12–16 fingers in 14–15 hands each. The bunch is densely arranged and weighed about 16–18 kg with 180–210 fruits

Monthan

Being moderately tall and robust, it can reach a height of 2.5–3.0 m. It carries a bunch of 18–20 kg within 12 months. Male flower of this variety is highly acceptable as vegetables. Considered one of the leading cultivars suitable for processing. The fruits are light green in color and have a valiant, knobbed, sturdy appearance with green peel. It can grow even under marginal condition having good salt tolerance ability. It is resistant to the Banana Bunchy Top Virus (BBTV), but susceptible to Fusarium wilt

1.8 BANANA BREEDING AND CROP IMPROVEMENT Bananas having diverse germplasms along with remarkable genetic differ­ ences traditionally cultivated in different regions all over the world despite their variations in genomic grouping still exist in the same group. Despite the significance of bananas as far as in terms of trade and commerce, there is exceptionally restricted data on the hereditary qualities for its agronomic significant attributes (Loh et al., 2000). In recent times, banana-breeding objectives are fundamentally limited on some significant viewpoints as portrayed by Robinson (1996): (1) Resistance against black sigatoka, races 4 of Fusarium wilt, burrowing to nematode and weevil borer and furthermore in decreasing the dependence on chemicals. (2) Increased dwarfness and stability comparative with “Grand Nain.” (3) Drought resistance to diminish dependence on irrigation. (4) Low temperature resistance (beneath 16°C) for the subtropical regions.

Banana

17

FIGURE 1.1 Glimpses of some important banana varieties. (A) Cheni Champa, (B) Octoman, (C) Peyan, (D) Pisang Rajah, (E) Pisang Ceylan, (F) Rasthali, (G) Ladisan, (H) Sabri, (I) Dwarf Cavendish, (J) Sakkarchyna, (K) Kothia, and (L) Grand Naine.

18

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

FIGURE 1.2 Characteristic bunch of few important banana cultivars of AAB genomic group grown in India. (i) Poovan, (ii) Nendran; (iii) Champa; (iv) Krishna vazhai; (v) Dudhsagar; (vi) Malbhog; (vii) Martaman; (viii) Chang Monua; (ix) Manohar, and (x) Kanai Bashi.

Banana

19

(5) Yield, harvest index and finger length to be better than “Grand Nain.” (6) Ripening, transport quality, and storability of fruits equivalent to or better than “Grand Naine.” Attempts were made on exotic cultivar assessment and selection at various research institutes working with banana and therefore Popoulu (AAB), Yangambi Km 5 (AAA), Big Ebanga (AAB) selected cultivars were released. Based on the investigation carried out by NRCB, Trichy on three hybrids (FHIA-01, FHIA-03, and FHIA-23) reported that FHIA-01 was substantiated itself as substantially more appropriate for handling alongside high sugar corrosive proportion and low polyphenol oxidation of the pulp which was liable for pulp carmelizing while FHIA-03 had more noteworthy agreeableness as cooking banana (Uma et al., 2006). Unconstrained spon­ taneous somatic mutants substantial freaks have assumed a critical role in the event of determination of specification (varietal improvement) and domestication of plantain and dessert banana. The wide ranges of bananas as well as the plantains that we cultivate and eat were dominatingly selected in ancient times from unconstrained mutations. From research outcomes it has been reported that more than six mutants have been perceived from the variety Nendran namely, Nana Nendran, Attu Nendran, Moongil, Velathan, Myndoli and Nenu Nendran, etc., while Harichal/Bombay Green, and Pedda Pacha Arati are the semi-tall sport of Dwarf Cavendish. Different examples of other banana mutants are Highate (AAA) and Cocos (AAA) are semi-dwarf mutants of Gros Michel (AAA); Motta Poovan (AAB) is a sport of Poovan (AAB); Ayiranka Rasthah is a sport of Rasthali (or Silk); Barhari Malbhog is a sport of Malbhog (or Silk); Krishna Vazhai is a natural mutant of Virupakshi (or Pome); and Sombrani Monthan (ABB) is a mutant of Monthan (ABB). Hybridization procedure in banana is difficult for its low pollen fertility, complexity in seed set and germination, but tremendous scientific effort and modern breeding techniques help to produce hybrids with three different crossing techniques like: I. 3N × 2N superior diploids, there is no chromozome decrease in the egg cells in this way yielding tetraploids. II. 4N reproduced tetraploid hybrids × 2N predominant diploids creating normal triploids III. 2N meiotic restoring clones × 2N prevalent diploids delivering natural triploids Another triploid combination namely, NPH-02-01 (AAB) was developed by Krishnamoorthy and Kumar (2005) between the cross of H 201 (AB) ×

20

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

Anaikomban (AA) which is not only parthenocarpic pome type yet in addi­ tion imperviously resistant to Fusarium wilt (race 1) and nematodes going with attractive yield attributing characters as like better bunch weight (19.00 kg) and hands (11.00). A fruitful attempt was made by KAU concerning Triploid and Diploid breeding, which prompted to release of two hybrids namely, BRS-1 (Agniswar × Pisang lilin) and BRS-2 (Vannan × Pisang lilin). It has been turned out for homestead cultivation in Kerala as it shows impervious resistant to Sigatoka leaf spot. Significant breeding work at the Fundacian Hondurena de Inves­ tigacion Agricola (FHIA) in Honduras is carried out for the development of improved diploids, those are again used as male parents in the crosses with female and fertile triploids for the production of tetraploids (Escalant et al., 2002). Major priority was given to in vitro ploidy breeding program to develop some improved potential diploid cultivars because production of diploid cultivars is not amiable to regular breeding strategies as on account of sterility in any case impervious to numerous stress with a decent yield potential ascribes. Hamil et al. (1992) achieved enlistment of autotetraploid by utilizing colchicine solution on in-vitro cultured explants of diploid Musa acuminata (AA) clone, SH3362. Improvement of commercial triploid cvs. Robusta (AAA), Rasthali Silk (AAB) through sexual hybridization is troublesome as these are female sterile. To resolve the previously mentioned problem, muta­ tion breeding was started in 1995 with such cultivars (Table 1.7). Kumar et al. (2004) detailed the capability of in vitro mutation breeding with cvs. Robusta, Nendran, Poovan, and Rasthali through gamma rays and EMS (ethyl methane sulphonate) and isolated numerous economic mutants. TABLE 1.7

Putative Mutants Obtained in Banana through Gamma Ray Induction.

Country

Parent Clone

Selected Clone

Selected Traits

Cuba

SH-3436

SH-3436-L 9

Height reduction

Parecidoal Rey

6.44

Height reduction

Lakatan

Lk-40

Height reduction

Latundan

LT-3

Larger fruit size

Sri Lanka

Embul

Embul-35 Gy

Earliness

IAEA

Grand Naine

GN35-I to GN35-VIII

Tolerant to toxin from Mycospherella fijiensis

Philippines

Banana

21

Somatic hybridization likewise effectively endeavored to tackle the problem of low seed setting in the significant number of the triploid culti­ vars and diploid crossings during creation of tetraploids. Regenerations of plants by protoplast culture were at first got accomplishment by the Bluggoe (ABB) cultivar (Sagi et al., 1995). Mutation breeding was recommended as a phenomenal elective alternative methodology for banana improvement. Since mutation gives an important valuable source of making variety in plant material, efforts have been made to stimulate it artificially by treating the corms, bits, corm-buds, suckers, and so forth. Lablanc et al. (1995) actu­ ated gynogenesis by irradiating pollen of M. balbisiana, M. ornata, and M. becarii. Conventional system to characterize banana plants by morphological descriptors has found such countless impediments. Lots of improved assort­ ments/varieties delivered have a complex genealogy which includes several wild species and landraces. Be that as it may, obstructions like immovable treatment, moderate to significant degrees of female sterility, and further­ more triploidy have made the identification of desired cultivars a main point of interest for banana improvement programs (Bhat et al., 1995). In case of developing proficient breeding schemes, extra steady information should be produced on the complex genome structure for hybrids as well as for cultivars. To this end, the characterization of indigenous germplasms will offer an exact method for forming taxonomic, phylogenetic, and heterotic groupings inside the family of Musaceae (Crouch et al., 1998). Cheesman (1948) first recommended that cultivated bananas originated through intraand interspecific hybridization between two wild diploid species namely, Musa acuminata Colla and Musa balbisiana Colla, every one of them contributing to the A and B genomes, respectively. The distinguishing proof program of Musa cultivars has generally been based on different combina­ tions of morphological, phenological, and floral criteria. Simmonds and Shepherd (1955) built up a scoring technique typically dependent on 15 diagnostic analytic morphological characters to differentiate M. acuminata clones from M. balbisiana cultivars and their hybrids into 6 genomic groups. The scientific categorization of developed bananas has for quite some time been an antagonistic issue and in light of the fact that it depends intensely on morphology, the literature shows numerous inconsistencies. For example, in view of molecular data based information, Pillay et al. (2000) recorded that the clones “Monthan Saba” and “Bluggoe” previously classified BBB group based on morphological attributes in any case, later it was demonstrated that really these two clones have a place with the ABB group. Comparative

22

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

occasion was found in occurrence of tetraploid “Klue Tiparot” (ABBB) which was again renamed as a triploid ABB (Jenny and Carreel, 1997; Horry et al., 1998). The difficulties related to the utilization of entire plant or botanical morphology have driven researchers to create different proce­ dures for the right identification of Musa species and cultivars. Onguso et al. (2004) revealed that various communities allude to similar nearby cultivars by various names and furthermore absence of clear clonal identity in the crop has brought about unnecessary duplication in cultivation, conservation, and research. But, in recent times, application of modern DNA finger printing techniques is suggested as one of the methods to select banana clones exactly and accurately (Robinson, 1996). Recommendation made available depicts that different DNA finger­ printing techniques have been utilized as more dependable, reliable alterna­ tive choice to study the genetic diversity and scientific classification as well as taxonomy of cultivated bananas which incorporate isozyme investigation (Bhat et al., 1992), restriction fragment length polymorphism (RFLP) (Bhat et al., 1994; Jarret et al., 1992; Kaemmer et al., 1992), rRNA spacer length heterogeneity (Lanaud et al., 1992), inter-simple sequence repeat (ISSR) markers (Godwin et al., 1997), sequence-tagged microsatellite sites (STMS) (Grapin et al., 1998; Kaemmer et al., 1997), and amplified fragment length polymorphism (AFLP) (Loh et al., 2000; Wong et al., 2001). Morphological and molecular characterization of the germplasms is an imperative requisite in the part of making the collection useful from the perspective of plant breeders. According to Nsabimana and Staden (2007) disadvantages of phenotype-based assays can be overcome by direct identification of genotypes with DNA-based markers. Molecular markers have been utilized commonly in Musa genotypes to asses ploidy (Oselebe et al., 2006), phylogenetic rela­ tionships (Jain et al., 2007; Nsabimana and Staden, 2007; Uma et al., 2006), and hereditary diversity or somatic diversity because of somaclonal variation (Lakshmanan et al., 2007; Bairu et al., 2006; Ray et al., 2006) or mutation induction (Hautea et al., 2004; Finalet et al., 2000; Toruan-Mathius and Haris, 1999). Polymorphis produced by RAPD analysis has been utilized for fingerprinting as well as classification of the Musa genotype. RAPD markers are typically alluringly liked as the techniques are too simple, extremely clear-cut, multipurpose, adaptable, quite modest, and ready to distinguish minute differences (Williams et al., 1990; Welsh and McClelland, 1990; Howell et al., 1994; Pillay et al., 2000). Linkage of RAPD markers to explic­ itly specific traits such as disease resistance has been conceivable through this procedure (Damasco et al., 1996) and RAPD-based fingerprinting has

Banana

23

been all the more anxiously, effectively, apprehensively, successfully applied to characterize diverse Musa germplasms (Bhat and Jarret, 1995; Onguso et al., 2004), analysis of Musa breeding populations (Crouch et al., 1999), and furthermore detection of somaclonal variants (Grajal-Martin et al., 1998). 1.9 SOIL AND CLIMATE Loamy, profound deep friable soil with characteristic of normal drainage and without compaction, is preferred for banana cultivation. Soils with poor permeation, percolation because of abundance of clay, rock, or sand must be avoided. Soils having pH somewhere in the range of 4.5 and 7.5 are vogue, albeit 5.8–6.5 is suggested. Soil textures ranging from sands to heavy clay are utilized. A granular soil structure is liked for better water movement and root development, with high organic matter and fertility guaranteeing significant returns. Most exported bananas are grown on profoundly fertile alluvial loamy top soils. Plantains are likewise best in this kind of soils; however, they will show improvement over the AAA dessert banana in degraded soils. Clearly, the “B” in their genome is liable for this versatility. Soil profun­ dity ought to be around 1.0–1.2 m deep. For better development moist soil with great soil drainage is fundamental; it does not endure standing water. Flooding for 7 days will kill most banana plants (Duarte, 1991). Banana will endure some saltiness: 300–350 mg/L of chlorine and up to 1500 ppm total salts. Banana accomplished a wide variety during the interaction of develop­ ment, regarding soil and climatic variation. With regards to world scenario significantly major banana growing territories are lying in between of the Equator and latitudes 20°N and 20°S. Bananas are grown fundamentally in tropical condition; currently it has spread into numerous subtropical environ­ ments with gentle winter, with relatively minute temperature variances from day to night and furthermore it proceeds from summer to winter season. The temperature ranging from 15 to 38°C prevails in the vast majority of the banana growing zones with an optimum temperature being ~27°C. The ideal temperature for dry-matter amassing or accumulation and furthermore for fruit ripening is accounted for about 20°C yet for the emergence of new leaves it is recorded about 30°C. Development ceases at 10°C and can lead to “chokethroat” disorders, where inflorescence emergence is hindered and poor fruit development happens. Though banana can survive temperatures under 15°C for short periods but temperatures below 6°C cause serious and

24

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

severe harm as well as occurrence of huge damage (Turner, 1994). It has been recorded and demonstrated that the harvest has a high water demand for its appropriate development and about 25 mm/week is viewed as the minimum for acceptable satisfactory growth. It has a good development in territories with 2000–2500 mm yearly precipitation, despite the fact that it can be cultivated easily in the regions with 600–1000 mm yearly rainfall with the assistance of drip irrigation system. Association of several physiological problems observed in colder subtropical environments is chokethroat, winter flower inception (referred colloquially as “November dump” in the southern half of the globe, inseparable from “May bundle” in the northern side of the equator), under peel discoloration (UPD), and growth cessation; these do not happen in the humid tropics. Moreover, the overall lack of wind, dust, storms, hail, or ice in the humid tropics implies that there are not many envi­ ronment instigated ranch debacles like those much of the time happening in the subtropics (aside from periodic floods and cyclones). This section on specific problems accordingly applies predominantly to banana-developing regions outside the humid tropics (Robinson and Sauco, 2010). 1.10

PROPAGATION

Seeds are generally used in breeding programs. Most of the world preferred cultivars have been confirmed to be female sterile. Suckers are used as planting material for their basal corm or whole corms. A sucker is a lateral shot with a basal corm and a small skewer that comes from the mother corm at the base of a vine. Normally small farmers use sugars or if few plants are required. Their height is difficult for suspenders, which makes it difficult to handle and carry. In comparison, disinfection is also inadequate to prevent the transport of insects, diseases, and nematodes. A young sucker that comes from the ground or a wide sucker with narrow leaves and a large corm is usually planted to the same depth with residual roots, and the excess leaves are cut back. Banana-exporting companies usually use corms from a plant that has not flowered and grow them in special nursery fields; these corms would weigh 2.5–5 kg. In other instances, 1.6–1.8 m tall sword suckers of 15–20 cm diameters at 20 cm from the soil are used. The suckers are dug out, and 15–20 cm of the pseudostem is held. If propagation material is scarce, large, older corms (bull heads) from flowering plants may be used for planting. Smaller corm bits may also be used. As part of good propagation steps,

Banana

25

pairing of corms to remove dark stains and any sort of root debris is to be done followed by dipping of pared corms in a fungicide, nematicide, and insecticide mixture for 5–20 minutes. A hot water dip at 56–58°C for 15–20 minutes or at 65°C for 12–15 minutes is used by major exporting firms. If pesticides are not available or are not permitted, merely paring the corms will help restrict transfer. Corms for planting should never be left on the field overnight; instead, they should be closely wrapped or transported in a trailer or truck to prevent reinfestation by banana weevil. 1.10.1

IN-VITRO PROPAGATION

Planting material of banana produced following in vitro techniques has been used commercially in most countries as a substitute to usual planting mate­ rial from 1985 onward. In certain Mediterranean and subtropical countries, in vitro planting material is now extensively used. 1.10.1.1 ADVANTAGES OF USING IN VITRO PROPAGATED BANANA PLANTS In case of in vitro propagation, 100% establishment rate is found which resulted in that there are no more replacements except somaclonal variants that are discovered after planting. No injury to root system will happen in this system; therefore, steady growth continues immediately after planting. Thus, it has been found that in vitro plant will have about 10 functional leaves even prior to their well establishment in field soil. As a result, these types of plants can be established more successfully in the field during each and every month of the year while most of the traditional suckers cannot estab­ lish properly during a winter season, and many more deaths occur if planting overlaps with wet summer conditions. In vitro plants in bags can be specially chosen for homogeny of size and shape. Uniformity/homogeny in flowering is one of the main characters of these plants and can all be harvested over a very short period making timing of the crop more accurate. Hwang and Ko (1987) opined that in vitro plants grow much faster along with larger pseu­ dostems and produce heavier bunches than that of the conventional suckers in first crop cycle. Nematodes, fungal, and bacterial infections are not found in plantlets grown in vitro. In vitro material, if planted in a treated soil, posi­ tively ensures less requirement of use of nematicides and fungicides.

26

1.11

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

LAYOUT AND PLANTING

The entire land should be prepared after thorough plowing and leveling done in the month of April–May. Usually, plantation is done in rainy season, that is, in the month of June–July. As well it can be planted in August to November or March to April. Before the plantation the land green manure crops such as dhaincha (Sesbania aculeata), cowpea (Vigna unguiculata), and others can be cultivated and buried in the soil. The plot must get a minimum of four to six plowing and then subject to weathering for 2 weeks. Use rotovator or harrow to break the clods and build a fine tilth in the soil. During final land preparation a basal dose of farmyard manure (FYM) should be applied and mixed into the soil. Topsoil mixed with well-decomposed FYM at 10 kg, 250 g of neem cake, and 20 g of carbofuron should be refilled in 45 cm × 45 cm × 45 cm pits. Azospirillum and Phosphobacteria both are applied in each and every pit with a dose of 20 g of each during planting and after that on 5th month after planting. Pre-emergence weedicide like Fluchloralin at 2 L/ha is sprayed done by a high-volume sprayer. Another alternative method practiced, that is, furrow planting is a form of planting that is done in a row. Depending on the soil strata, the appropriate form, positioning, and depth at which the plant must be planted will be chosen. Before planting Hill Bananas, the jungle must be cleaned and contour stone walls built. Traditionalist banana farmers sow the plant at a high density of 1.5 m 1.5 m; however, plant growth and yields are low due to increased competition for sunlight. The planting distance should be above the range of 2.1 m × 1.5 m in regions such as north India, the coastal belt, and where the humidity is very high and the temperature drops to 5–7°C (Table 1.8). TABLE 1.8

Standard of Planting Geometry for Different Banana Cultivars.

Varieties Grand Naine, Dwarf Cavendish

Spacing

Number of Suckers/ha

1.5 m × 1.5 m

4440

1.8 m 1.8 m

3086

Rasthali, Poovan, Ney Poovan, Karpooravalli, Red Banana, Monthan

2.1 m × 2.1 m

2267

Hill Banana

3.6 m × 3.6 m

771

Robusta, Nendran

The planting time plays a pivotal role in banana plantation, so that the time of planting must be adjusted consequently to prevent drought and

Banana

27

high-temperature effect during bunch emergence (i.e., imprecisely 7–8 months after planting). 1.11.1

HIGH-DENSITY PLANTING IN BANANA

High density planting is in a horticultural manner by which plants can be planted in numbers ranging from 4444 to 5555 per hectare, with a yield of 55–60 tons per hectare or even more (Table 1.9). Conventionally, general cultivators used a square or rectangular planting pattern. Planting three suckers per pit for Cavendish varieties at a spacing of 1.8 × 3.6 m (4600 plants per ha) and 2 × 3 m (5000 plants per ha) for Nendran varieties is also practiced. TABLE 1.9 Comparison between Planting Geometry Followed in Normal and HDP of Important Banana Cultivars. Varieties

Normal spacing Spacing (m) Population/ ha

High density planting Yield (t/ ha)

Spacing (m)

Population/ ha

Yield (t/ ha)

6944

174.39

Robusta

1.8 × 1.8

3086

114.36

1.2 × 1.2 1.5 × 1.5

4444

145.44

Dwarf Cavendish

1.8 × 1.8

3086

102.34

1.2 × 1.5

5555

166.66

Poovan

1.8 × 1.8

3086

31.50

1.5 × 1.5

4444

37.80

1.12

IRRIGATION

It has been well documented from researches of several scientists that banana plant claims about 900–1200 mm of water in its entire life cycle through natural precipitation (rainfall) as well as from supplementary irrigation. Maintaining optimum moisture level or water retention at all stages of the growth is intensely or severely crucial. But, more crucial thing is to have a good drainage system in banana plantation to remove excess water from the plant's root zone to promote improved growth and productivity. Irrigating the plant every 3–4 days during the hot summer months and every 7–8 days during the cooler months is usually recommended. However, if irrigation is needed during the rainy season, do so; otherwise, do not irrigate cropping land because excessive irrigation or water saturation in the root zone of the

28

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

plant can cause root zone congestion or condensation due to the removal of air from soil pores, affecting plant establishment and development. In banana plantations, many methods of irrigation are used, including flood or furrow irrigation, trench irrigation, drip irrigation, and fertilization, each with its own set of benefits and drawbacks. Being a delicious, succulent, evergreen, and shallow rooted crop it requires enormous amount of water for thriving the profitability level up to a stature. Water necessity of banana has been worked out to be 1800–2000 mm for every annum. In all, around 70–75 water systems are allowed to the crop in all its entire life cycle. Importance and relevance of drip irrigation and mulching techniques has reported to be substantially more beneficial in banana cultivation regarding improvement of water use effectiveness or efficiency. In drip irrigated banana orchard, water is saved up to 58%, maturity advances up to 1 month, and yield expanded by 23–32% which has been verified by a number of scien­ tists (Table 1.10). Next to each other, the drip irrigation likewise empowers effective fertilizer application through the fertigation method. Drip irrigation system might be given in a schedule as like at 15 L/plant/day from the time of planting to fourth month, 20 L/plant/day from fifth month till shooting stage, and 25 L/plant/day from shooting stage to only 15 days preceding harvest. Two sorts/types of drip irrigation system continued in banana are single-line system (pertinent when the planting geometry is followed at 1.5 × 1.5 m spacing and here one horizontal/lateral line and one dripper per plant is used) and double-line system (appropriate when the planting calculation is followed at 1 × 1.5 × 1.8 or 2.1 or 2.4 m spacing as distance between the lines, between two plants, and between two double lines, respectively. Here one lateral and one dripper for two plants are orchestrated). TABLE 1.10 Drip Irrigation Schedule for Banana. Sl. No. Crop growth STAGE

Duration (weeks)

Quantity of water (L/ plant)

1.

After planting

1–4

4

2.

Juvenile phase

5–9

8–10

3.

Critical growth stage

10–19

12

4.

Flower bud differentiation stage

20–32

16–20

5.

Shooting stage

33–37

20 and above

6.

Bunch development stage

38–50

20 and above

Banana

1.13

29

NUTRIENT MANAGEMENT

Growth rate of banana is faster than others and it requires generally enor­ mous quantity of nutrients for its higher qualitative yields (Table 1.11). Lahav and Turner (1983) reported, according to assessment, that 50 tons of banana from one hectare of land eliminates 320 kg N, 32 kg P2O5, and 925 kg K2O each and every single year. Application of inorganic fertilizers however increases the yield, probably yet it could not be able to hold up the fertility status of the soil (Bharadwaj and Omanwar, 1994) and have caused a few undesirable consequences and results in the delicate soil eco-system, prompting deliberate decrease in profitability level. In recent times, several researchers directed and suggested coordinated methodology of supplement integrated approach of nutrient management in banana to hasten yield possibility, as RDF100% (200:100:300 g N:P2O5:K2O + 20 kg FYM per plant) + PSB (20 g) + Azospirillum (20 g), as detailed by Pattar et al. (2018). Banana has been found to react well to potash spray provided through muriate of potash (MOP) or potassium dihydrogen phos­ phate (KH2PO). The combined impact of these supplements, urea, sulfate of potash (SOP), and cowdung as a post shooting applicant in banana has been evaluated earlier at Indian Institute of Horticulture Research, Banga­ lore (Adinarayana et al, 2016). TABLE 1.11 General Fertilizer Recommendations for Orchard Land and Wetland Banana. Details

N (g/ P (g/plant) plant)

K (g/plant) Micronutrient

Orchard land Varieties other than Nendran

110*

35*

330*

Nendran

150

90

300

Nendran

210

35

450

Rasthali

210

50

390

Poovan, Robusta

160

50

390

Wetland

At 3, 5, and 7 months after planting, foliar applications of ZnSO4 (0.5%), FeSO4 (0.2%), CuSO4 (0.2%), and H3BO3 (0.1%) help to improve banana yield and efficiency

Apply 50% more fertilizers to tissue culture bananas at the 2nd, 4th, 6th, and 8th months after planting.

*

30

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

1.13.1

FERTIGATION IN BANANA

Fertigation is the interaction where fertilizers are applied through irrigation system framework. Completely solvent nitrogen and potassium used to feed at the rate of 150 g for every plant is sufficient to meet the nitrogen and potassium for obtaining adequate yield. Use of nitrogen as urea and potas­ sium as muriate of potash (MOP) through this framework system could be profitable. These fertilizers are permeable into the system subsequent to shaping a fertilizer solution in the tank. The fertilizers might be endowed into the system either on a consistent schedule of daily basis or in a customary regular interval of per week and it could be stopped 10–15 days before the harvesting. Several formulations of water-solvent fertilizers are now acces­ sible on the local markets. A very definite determined specified formulation for banana crop indispensably dependent on the crop growth stage can likewise be chosen for fertigation (Table 1.12). TABLE 1.12 Commonly Followed Weekly Fertigation Schedule for Banana. Sl. No.

Crop stage

Weeks after Planting

Urea

Total (g/ plant)

1.

Establishment stage

9–18 weeks (10 weeks)

15

150

MOP Total (g/ plant) 8

80

2.

Vegetative stage

19–30 weeks (12 weeks)

10

120

10

120

3.

Shooting stage

31–40 weeks (10 weeks)

7

70

12

120

4.

Development and 41–46 weeks (5 weeks) harvesting stage

Nil

Nil

10

50

–

340

–

375

Total

1.14 TRAINING AND PRUNING Training practices to give plants alluring shape is not rehearsed in the case of banana mostly because of its pseudostem-based developing propensity or growth habit and cyclic leaf emergence. Other than the removal of the male inflorescence, no other vegetative pruning is ordinarily followed. Wilted styles and perianths persisting toward the end of the fruit are typically eliminated at the packing station after collection through harvest; however, sometimes these are taken out by hand 8–12 days later of the bunch emer­ gence, to reduce fruit scarring and disease (cigar-end rot). Early evacuation

Banana

31

or removal or expulsion of at least one hand from the distal end of the bunch is politely practiced to expand fruit size by diminishing between finger and hand rivalry. This hand expulsion is done by the export organizations for dessert bananas and plantains to accomplish better calipers (fruit diameter— size) in the remaining fruit. Bunches tumbling from the plant or the entire plant falling over can prompt significant hand damage and can lead to rejec­ tion of the affected fruit for trade. Lodging is due to poor corm anchorage, poor planting material, or very large bunches. The issue is decreased if single or double shafts/poles are wedged against the throat of the plant under the curvature of the bunch peduncle or twine guys are stretched out from this equivalent point the other way of the fruit bunch and tied for attachment to bring down positions on close by plants. 1.15

INTERCROPPING AND INTERCULTURAL OPERATION

Intercrops can easily accommodate in the field of the banana plantation at the early stage of growth. Mixed cropping of banana, arecanut, and coconut is generally practiced in some belts, especially in the coastal belts of Tamil Nadu in India. Different types of intercrops like maize, brinjal, colocasia, chillies, turmeric, spinach, bhendi, radish, cabbage, cauliflower can be followed in the banana plantation based on climatic conditions. Banana plays a pivotal role as a shade plant in coffee, cocoa, rubber, young mango, and orange plantation of different parts of the state. For better growth and development of the plant, spade digging should be given at bimonthly intervals and also earthing up should be done periodically. Another thing to do with priority is periodical removal of side suckers at regular interval. The dry and diseased leaves are to be expelled and also burnt to manage the stretch out the severity of leaf spot diseases. Male flowers should be removed 1 week after the opening of the last hand in case of Robusta banana to elude “Cigar end rot.” Similarly, flower remains must be removed a week after the last hand’s opening. At the flowering stage the plant may be propped. The peduncle should be topped with flag leaf to prevent end rot of main stalk. To protect the plants from sunscald, bunches may also be covered with banana leaves. 1.15.1

DESUCKERING

Evacuation or in terms of removing all of the suckers from the mother plants up to flowering and subsequently keeping only one follower afterward is

32

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

the excellent desuckering practice. Desuckering or pruning generally is the practice of removal of unwanted suckers. Here, newly grown suckers have to be cut off or destroyed at their heart position without separating the sucker from the mother one. In some cases, after digging the sucker three to five drops of kerosene is poured into the cavity. Destruction of suckers by using crow bar with a chisel-like end is general practice in South India. 1.15.2 TRASHING It is the act of expulsion of undesirable material from banana field as dried, diseased, and rotted leaves, pseudo stem after harvest, male bud, last end of inflorescence, and wilted botanical parts especially floral sections. 1.15.3

MATTOCKING

Soon after harvesting of the bunch, the plant stem ought to be cut in stages at any rate following 30–45 days to encourage activation of the supplements basically nutrients from the mother for the growth of ratoon plant. This prac­ tice of keeping certain portion of stump about 0.6 m height for nourishment of second-generation crop is generally termed mattocking. 1.15.4

BUNCH COVERING

Covering of the banana bunch isn't just the actual physical protection technique yet additionally it improves the perceptible quality of fruit by advancing skin coloration and diminishing blemishes, anyway it can likewise change the micro-environment for advancement of fruit growth that can have a several gainful beneficial consequences for internal fruit quality. Bunch cover can likewise debase the frequency level of infection, which may arise from insect pest, disease, mechanical damage, sunburn injury to peel, fruit cracking, agrochemical residues on the fruit, and furthermore those sorts of harm brought about by birds (Fig. 1.3). The covering of bunches has now taken place as a huge cultural practice in the arena of commercial banana production. The suggested sort of bunch cover shifts variously as indicated by the natural conditions. Bunch covers specified for banana should have appropriate measurements like made up of low thickness polyethylene (5–40 µm) and are 81.3–91.4 cm wide and of 1–1.5 m long. The slender thin bunch

Banana

FIGURE 1.3

33

Difference in resultant banana bunch grown with and without bunch cover.

34

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

covers are significantly and logically intended to be utilized just once yet the thicker pack covers can be re-utilized; however, the evacuation cycle of removal process is tedious and it hushes up unwieldy to eliminate it securely without evasion of harming the plastic sheet. Most of the commercially available bunch covers in the market are white colored or translucent blue. Silver-colored plastic may likewise be found in the market which reflects heat (Santosh et al., 2017). 1.15.5

REMOVAL OF MALE BUDS (DENAVELLING)

Removal of male bud after the end of female phase is referred to as “Dena­ velling” or “Tipping” which aids fruit growth and raises bunch weight. Male buds are taken out from the last one to two small hands with a well put cut together keeping a solitary single finger in the last hand. The infertile male flowers of banana generally protected under reddish scale leaves thus formed a large heart-shaped flower bud, tending to persist even after the fertile blossoms have formed and shaped into a bunch. Along these lines, it is important to eliminate the male bud as and when the bunched is shaped and also formed; or, more than likely it is probably going to go through a portion of the food, which would somehow or another go to the improvement of fruits. This practice is additionally suggested for preventing fingertip disease and thereby improving the appearance of the bunch. 1.15.6

DEHANDLING OF FALSE HANDS OF BUNCH

The incomplete hands of the bunch which are not fit for quality production need to be removed soon after bloom. The false hands are also needed to be removed. Removal of these incomplete hands as well as the false hands helps to improve the weight of the other hands. 1.15.7

PROPPING

Propping is a necessary intercultural operation to give the plant proper shape and size and avoid lodging. It aids in the growth of a bunch in a consistent manner. This could be done by placing bamboos in a triangle against the stem on the leaning direction.

Banana

1.15.8

35

REMOVAL OF FLORAL REMNANTS

The persistent dried floral parts may provide shelter of fungal spores and help in spreading different fungal pathogen, and thus need to be removed from the tip of the fruit or finger. 1.15.9

PEDUNCLE WRAPPING

As peduncle is connected between the developing bunch and the plant for nutrient supplement and water, taking consideration for peduncle is an important activity during the bunch maturation period to evade scorching injury. Immature ripening and falling of bunches is the sign of affected peduncle. Wrapping the peduncle with leaf trash or flag leaf during hot summer days is necessary to avoid the direct effect of heat generated for exposing to scorching sun. 1.15.10 EARTHING UP Earthing up of banana plantation is done 2–3 months after orchard estab­ lishment; it assists with creating uniform establishment of the plant and furthermore assists with dodging water logging at the base of the plant which moreover protects the plant from soil or water-borne infections. 1.15.11 WEEDING Weed infestation is one of the serious hindrances in banana orchard, periodical weeding is necessary to check the plant weed competition that in return gives optimum productivity of the crop. Application of different pre-emergence and post-emergence herbicides may give better results if manual weeding is not possible. Mulching (jute/plastic) may provide better result to check the weed population as well as to conserve the soil moisture. 1.15.12 REMOVAL OF DEAD LEAVES Sanitation of orchard is the prerequisite to obtain quality production. As dead leaves serve as a secondary source of infection for different pathogen,

36

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

it needs to be ensured to remove all the dead leaves keeping at least 6–8 healthy leaves/plant to ensure maximum bunch development and optimum harvested banana green life. 1.15.13 GROWTH REGULATOR APPLICATION Application of plant growth regulators (PGRs) like 2,4-D (25 mg/L) during last hand has helped to improve the grade of the bunches. The same spray is also applicable to develop seedless banana in certain varieties like Poovan and CO-1. To increase the yield potentiality CCC @ 1000 ppm at 4th, 6th months after planting and plantozyme @ 2 mL/L at 6th and 8th months after planting may also be recommended. 1.16

FLOWERING AND FRUIT SET

Banana inflorescence starts its development inside the pseudostem and at the end of vegetative stage it comes up as inflorescence from apical meristem, a flattened dome in which the main meristem lies deep inside. Flowering is only possible after the phases of broadening of the apex by both division and expansion of cell. Floral initiation indicates its sign as meristem becomes convex and rises above the surrounding leaf bases. Flower bracts appear as a replacement for leaves. During the initiation of the inflorescence an immense increase in mitotic activity deep in the corpus and thickening of the tunica has happened. As a result of all this activity, finally, we find a stem with elongated internodes, nonencircling bracts in place of encircling sheaths, and a regular system of axillary lateral branches—the flowers (Simmonds, 1966; Stover and Simmonds, 1987). By figure, before floral initiation, the meristem undergoes production of a leaf and a lateral bud (phytomer) every 10 days, but after floral initiation it produces a bract and up to 20 flower initials every 1–2 days. The axis of the inflorescence, which is terminal on the corm, is located at the distal end of the aerial stalk. Banana inflorescence is typically a raceme or spike comprised of cymose clusters of flowers at nodes enclosed in colored bracts. Three types of flowers are positioned in the same inflorescence in a synchronized way as female flowers are within the basal (proximal) bracts and the male flowers in the apical (distal) bracts; the intermediary clusters or neuters are in transitional position. Musa plants are monoecious as they predominantly bear unisexual flowers. Geitonogamous pollination may

Banana

37

take place between inflorescences on the one clump or mat. In the juvenile inflorescence, distinguishing factor for nodes of male and female flowers is characterized by a sharp reduction in ovary length from one node to the next. The principal biochemical processes that ultimately are responsible for the formation of different types of flowers must take place much earlier in the sequence of floral differentiation. Male and female flowers are differentiated on the basis of their ultimate fate as female ovary is larger having a massive style that exceeds the perianth in length, and the stamens are reduced to staminodes whereas in the male flowers the ovary is small and in many culti­ vars and species they develop an abscission zone at their base and are shed after few days of anthesis. The female flowers are without such abscission zone; however, the style and staminodes may abscise, leaving a calloused scar at the top of the ovary (Stover and Simmonds, 1987). Depending on genotype, environment, and edaphic condition, the inflorescence bears 1–30 nodes (or hands) of pistillate female flowers, followed by 0–4 hands of neutral flowers or pseudohermaphrodite hands. The remainder of the inflorescence contains staminate flowers, comprising of 150–300 hands. There is a tendency of the apex to produce male flowers continuously long after the female fruits have rotted. Development stops just after the bunch emerges from the top of the pseudostem. It happens in some clones, especially among plantains where the apex is short lived. Exception­ ally, the horn plantains are characterized by the absence of male flowers at maturity (Simmonds, 1966; Stover and Simmonds, 1987; Swennen et al., 1995; De Langhe et al., 2005). Nature of the blossoming upgrade is obscure and stays the subject of significant theory or speculation. It is probably not going to be temperature or photoperiod related, in light of the fact that flowers are initiated in every month all year long in the subtropics, where large temperature and photoperiod gap or fluctuations prevail. Though several conflictions exist, it is presumed that inflorescence can be initiated after the production of 25–50 leaves. There might be a readiness to flower’s communication in which the rhizome more likely than not arrived at a basic critical phase of develop­ ment and a specific “minimum functional leaf area” probably must have been created. The trigger for flower initiation commencement could then be hormonally induced. Recent perceptions (Hernández et al., 2008) demon­ strate a buildup of gibberellic acid (GA3) in the rhizome after emission of leaf 21 (flower inception at leaf 27) on plantain (AAB cv. Hartón). This may demonstrate a job of GA3 in the cycles of meristematic change and genuine stem elongation; however, this hypothesis actually must be tried and

38

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

confirmed. In a new report by Chaurasia et al. (2017) on cvs. Stupendous Nain (AAA genotype) and Hill banana (AAB genotype), it was conceivable to confine the 12 FLOWERING LOCUS T (FT) and two TWIN SISTER OF FT (TSF). This study likewise proposes the expression at any rate of three genes in particular MaFT1, MaFT2, and MaFT5 (and somewhat MaFT7) elevates only before the inception of flowering. These four genes and five others (MaFT3, MaFT4, MaFT8, MaFT12, and MaTSF1) could restrain the deferred flowering imperfectionally defect in the Arabidopsis ft-10 mutant and responsible for actuating early flowering upon over-articulation in the Col-0 ecotype. Connections of relationship of banana FTs vis-à-vis Arabidopsis may likewise be executed through the clues got from the inconspicuous stuble amino acid changes in these FT/TSF-like proteins. Several extraordinary data of this study encourage researchers to work regarding flowering regulation in banana by improved resource management and to decrease misfortunate losses through abiotic stresses and advocated supporting banana flowering is directed by a minimum of three homologues of FLOWERING LOCUS T. 1.16.1

POLLINATION

About 4000 pollen grains are needed to cover the stigmatic surface of the female flower for effective pollination (Dodds, 1945), which is roughly about 20–40 times of the ovules in an ovary. The pollen tubes transverse the entire length of the style after 12 h of pollination. The length of the style is 30 mm, so the rate of development is 0.33 mm/h. Via the micropyle, the pollen tube joins the ovule. The styles abscise about 30 h following the maturation of their receptive surfaces. Fertilization must be done within 24 h of flower opening because after this stipulated time period flowers start to crumble. 1.16.2

POLLEN GERMINATION

Till now, little information is available regarding banana pollen germination. In India, pollen germination of 18 tetraploid (AABB) banana hybrids in in vitro condition was carried out by Krishnamoorthy and Kumar (2005) and their findings concluded that 4–17% germination was noted; however, 84% pollen germination was found in diploid banana (Nyine and Pillay, 2007) in Uganda. Percent germination of pollen is not related to the pollen production

Banana

39

of the plant; thus, amount of germinable pollens could not be predicted based on the amount of pollen production. 1.16.3

POLLINATORS

Several pollinators are associated with banana pollination. Though bird and bats are the key pollinators but several other pollinators are also associated with it which includes tree shrews (Tupaia sp.) and bees (Trigona sp.). In Musa spp. the male flowers have shorter flowering time than female flowers and as bananas produce flowers throughout the year, vertebrate pollinators are attracted by them easily. The timing of anthesis and the crest nectar production by flowers are steady with pollinators being present during the daytime (birds) or at night hours (bats). Seed set in Musa acuminata ssp. halabanensis (chiropterophily) and Musa salaccensis (ornithophily) was pollinator limited (Itino et al., 1991). Equal pollination by birds and bats was noted in Musa itinerans in southern China (Liu et al., 2002). 1.16.4 FRUIT SET The banana fruit can be characterized botanically by a berry, but is produced from a lower ovary. This epidermis and aerenchym coating is created from the exocarp, the mesocarp contains the pulp and the endocarp is contiguous to the ovary cavity and is limited to the inner epithel. For the growth of fruit, pollination is important in wild grain bananas, where mature fruit has an overall black seed surrounded by sweet pulp from ovary and septa areas. It is unlikely to grow seeded bananas if they are shielded from pollination. On the other side, the vegetative parthenocarpy means edible bananas produce where there is no pollination to grow the mass of edible pulp. The ovarian cavity has three locules. Pollen sterility is caused by triploidy and at least three complementary mainstream genes and modifier genes have resulted in female sterility. These sterility genes have been selected for fruit edibility in wild populations. In banana, ovules are increased by 50% of their initial size within first fortnight after anthesis, and after that they gradually shrink and growth of ovary reduces. In some instances, fruit growth in parthenocarpic bananas with seeds (“Pisang Awak” ABB) has also been observed and it may be due to the stimulus of developing seeds, whereas report is also available on fruit growth only for stimulus of pollination even without development of seed

40

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

(Israeli and Lahav, 1986). There are periclinal and anticlinal divisions from about a month and a half (6 weeks) before inflorescence emergence (anthesis) to about a month (4 weeks) after emergence. This division is followed by cell expansion for about 4–12 weeks after rise. Skin mass increases quickly in the initial 40 days in the wake of blooming, with the fruit pulp not starting to create until day 40. Starch amassing parallels finger length and diameter measurement increases (Lodh et al., 1971). The fruit takes 85–110 and 210 days from inflorescence emergence for maturity in the tropics and in the cooler subtropics or under overcast conditions, respectively. 1.17

RIPENING, FRUIT GROWTH, AND DEVELOPMENT

The life span of a banana during its green state is limited to the time between harvest and the visible phase of the respiratory climacteric cycle. From the commercial perspective, main consideration ought to be paid to drag out this period as far as might be feasible and this is accomplished from various perspectives like harvesting at early stage of fruit maturity, providing transportation facility of low temperature control (13°C). It is also possible to increase the preclimacteric phase by hormone therapy (gibberellin) or by storage in a modified/controlled environment (CA) as well as ethylene scrubbing. The respiratory peak (climacteric) is recognized by quick O2 take-up and CO2 evolution to a greatest pace of 250 mg CO2 kg/h from a preclimacteric low of around 30 mg CO2. Presumption of time prerequisite to touch the pinnacle of preclimacteric state is certainly not a single factor subordinate phenomenon, rather it relies upon temperature, humidity, and ethylene concentration. It is evidenced from different findings that the accel­ eration of ripening process takes place when the respiratory maximum is attained, whereas the respiration rate diminishes progressively to attain at zero at the physiological demise of the fruit. Once started or just initiated, the climacteric is irreversible. 1.17.1

RIPENING PHYSIOLOGY

Ripening of any fruit is a resultant of several physiological processes. During progression of fruit maturity several conspicuous changes take place concurrently and ultimately make the fruit a ripe one. Out of so many physi­ ological changes, tissue softening commences first in the ripening process, when starch is converted into sugars in both the pulp and the peel, causing

Banana

41

the strength of the cell walls to decrease, cracks to form, and the cells to collapse and degenerate. Furthermore, elevated concentrations of soluble pectic polysaccharides and uronic acid, as well as their associated enzyme activities, are seen. Color changes in the peel of the fruit from dark green to light green and afterward to yellow as chlorophyll is separated or broken down. In course of color change, the pulp becomes more soft and sweet as concentration of sugars tends to be in higher site than starch and in this phase a characteristic aroma developed. All these changes are dependent on several numbers of enzymes. Finally, due to progression of ripening process, the peel becomes spotted brown colored and afterward totally brown colored and the pulp loses its firmness, white surface to get brown colored and thick geltinous. There is a color graph for ripening bananas in the retail trade that contains seven stages. Here, “Stage 1” denotes hard green organic product with starch content of significant level and “Stage 7” marks delicate yellow fruit with brown-colored specks and high sugar content. The term of “green life” compares to the shading Stage 1 to the furthest limit of Stage 3, though the span of “shelf life of realistic usability” relates to the color Stage 4 (natural product more yellowish than green) to an extended limit of Stage 7. This, thus, relies upon capacity temperature and infectious like disease prevention. 1.17.2 ARTIFICIAL RIPENING If mature banana fruits are allowed to ripen naturally these will ultimately soften and most of the cases develop dull and unattractive peel. To solve these problems of natural ripening, in commercial aspect bananas are subjected to artificial ripening treatment with exogenous ethylene. These also additionally serve the purpose to get a firm pulp texture, good flavor, bright yellow peel color, and uniform ripening. In recent times, banana traders' expertise was used in ripening the banana in closed chambers with air renewal/recharging, controlled temperature and moistness, ethylene injectors, and outfitted with specialized devices for observing and measuring CO2, temperature, and relative humidity. The ripening interaction comprises three phases, that is, (i) temperature increase, (ii) ethylene infusion, and (iii) ventilation while diminishing temperature. At a convergence of 1000 ppm and at the optimal beginning temperature, ethylene gas is administered to green fruit. After that, the rooms are fixed for 24 h before the doors are opened, air is re-established/ renewed, and the rooms are ventilated day by day to remove CO2 that has been collected during the ripening cycle, while temperatures are gradually

42

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

dropped. When the fruits reach color Stage 4, the pulp temperature should be at 13–14°C, and the fruits are removed from the chamber. During the whole ripening phase, relative mugginess should be maintained at 95%. 1.18

HARVESTING AND YIELD

After passes through the development and maturation stages, fruits of banana enter into the ripening stage where special experience and care should be needed to judge the optimum harvesting stage. After harvesting if the bunches are handled carefully and transported to the market safely with modern packaging, there is an obvious opportunity for premium return. So, harvesting of banana bunches at optimum stage, proper handling during transport, optimum packaging, and good storage facility are prerequisite to safe disposal of fruit in market. 1.18.1

FRUIT MATURITY STANDARDS

Principles of fruit maturity rely upon a few components like cultivar, agro­ ecological circumstance of grouping spot, distance of transport, inclination of the customer, and so on. For instance, fruit could be harvested at completely mature stage for immediate ripening and local business. For on-location showcasing or short-distance transport of green fruit, 90% of complete maturity might be used, whereas 75% maturity is commonly used for medium-distance delivery by truck. Exporters and growers judged the 75% maturity with characteristic “3/4 round” finger, that is fingers still having articulated ridges but with convex planes between them. Banana bunches of under 75% maturity are liked for significant distance transport by ship. This strategically techniques of maturity judgment verifications is required as permitting fruit to get over matured during warm climate can lead untimely premature ripening during transport. Similarly, too soon or early harvesting of immature bunch in cool climate can lead to a few kilograms loss of bunch weight and expanded maturity as well as ripening necessities. Among the developed and tested approaches to determine the optimal harvest stage, majorities are ruinous, harmful, unfeasible, impractical, or subjective. As an example, consider the pulp-to-peel ratio, and an immovability firmless index of fruit skin. Till date the “3/4 round” index continued in numerous subtropical nations is sealed good for the nearby market shipment; however, it is difficult to keep up its precision accuracy and consistency. Be that as it

Banana

43

may, the most adequate functional and target strategy for normalizing harvest maturity is with a mix of phenology (expected bloom rise to harvest dura­ tion span (E–H)), shaded strips, and caliper estimation of finger diameter measurement. This strategical methodology, first rehearsed in global organi­ zation manors of Central America, is presently regular in many locales where fruits go to top notch trade markets or export market. Bunch coverings made up of colored polyethylene strip or woolen thread are placed 14 days after flowering, affixed to the peduncle. Every week another color tone is utilized on new blossoms, at that point, following 2 months, the shading succession is rehashed. The main benefit of this procedure is that week-by-week bloom checks can be made dependent on the quantity of labels utilized, and these tallies structure the premise of yield anticipating. Second, harvest control and arranging plans are made simpler. In the tropics, normal E–H ranges between 98 and 115 days (Stover, 1979). As a result, 91 days after flowering during the hottest season, bunches with the matching precise color code are tested with a caliper for harvest maturity (finger diameter), and a few of bunches may be cut. As top hands mature snappier than basal hands, caliper estimation is constantly made on the center finger of the external whorl of the second hand to have a normalized standard estimation. As indicated by proper color accomplishment of bunches, consecutive cutting of bunches will be done at 98 and 105 days. Further, the selected bunch as indicated by colored code is checked with the caliper estimation that should be in the range of 31 and 41 mm. During fruit development period, when the cool environment prevails the main caliper estimation might be done following 105 days because of a more extended E–H. Regarding market inclination, the USA market favors marginally more full fruit than the European market, inside the 31–41 mm caliper range. Another opinion on harvest index fixation by Ganry (1978) stated that prediction of harvest date might be done with the help of calculating “total daily temperature” (TDT) only if we nullify the possibility of occurrence of edaphic and phytopathological constraints. For Cavendish cultivars, TDT is calculated using a 14°C threshold, which is the growth limit of lowest mean daily temperature. TDT is calculated following the given equation: TDT = ∑ [(daily Tmax + daily Tmin/2) – 14 where Tmax = maximum temperature and Tmin = minimum temperature, for a given day, respectively. According to findings of several experiments, a TDT temperature of 900°C (measured from the first female hand open to the emergence stage)

44

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

is optimal for banana bunch harvesting (three-quarters round stage with a 34-mm caliper measurement), whereas TDT of 1200°C is used as an indi­ cator for the full round stage. In France and West Indies, farmers practice both TDT and caliper measurement for more accuracy (Lassoudiere, 2007). Flawlessness or precision of the TDT relies on the use of a sophisticated digital thermometer or temperature sensor, as well as a weather instrument shelter/cover (Ganry and Chillet, 2009). In Indian conditions, banana bunches usually take 90–120 days to develop after shoot initiation though a clear difference on time requirement exists for tall and dwarf cultivars for harvesting the bunch after planting; it is 14–16 months and 11–14 months for the first and second categories, respectively. For commercial dessert bananas all through the world, the harvest strategy follows a comparable method example, with minor variations. Exportable bananas like Grand Naine, Cavendish have yield potentiality in the range from 50 to 100 t/ha, though these cultivars generally produce 65–70 t/ha. Otherwise, yield of banana varies in a wide range for difference in cultivars and area of production. 1.19

PACKAGING AND TRANSPORT

First-grade bananas are packed into cardboard containers as entire hands, bunches or singles, and the stuffed container mass can range from 12 to 18 kg, contingent upon nations and markets. In India, CFB solid boxes with 13-kg limit are ordinarily utilized in banana transportation. Containers like cartons should be comprised of required determination of which powerbearing capacity of palletization and arrangement of ventilation to keep a uniform temperature during refrigerated shipment is cared most. Pack­ aging of hands or bunches ought to be done in a perfect, normal example to lessen development and scraping; hence, containers should be full yet not overfull. Cushioning pads (as a rule of general that kraft paper or plastic) are embedded to ensure protection of fruits in between the concerned rows. Polyethylene film liners are regularly utilized in export fruit containers like cartons to limit water misfortune and to give a protected safeguard from scraped area harm during transport. To remove oxygen, air may also be sucked out from the liner. Banana export markets in the EU are particularly demanding in terms of fresh fruit use. EU Directive 2257/94 (EURlex, 2010) is carefully followed with respect to fruit quality, presentation, and stamping, for Cavendish bananas imported to EU markets.

Banana

45

1.19.1 TRANSPORTATION In major banana-exporting countries, refrigerated trucks are generally used to transport fruit to ships, where pallets are carried to refrigerated holds. Refrigerated transportation is fundamental to keep green fruit from starting the ripening interaction before landing in the destination. Fruits ought to be set into the cold chain inside 24 h of harvesting (generally called the “cut to cool” period), yet the compelling outcomes acquired on the off chance that it is finished within 8 h time span. As concern the varietal reaction, it was seen that 13–14°C is ideal to forestall ripening without causing chilling injury for Cavendish bananas, and 10–12°C might be better for bananas of the “Prata” subgroup. Evidently, the B genome provides better cold resistance both in the field and during transit (Lichtemberg, 2001). Reestablishment of air to dodge ethylene accumulation is fundamental during transport. The recommended rate of air renewal is 30 times the capacity of the container/h (Lassoudiere, 2007). Prior to stacking the refrigerated container (reefer), ventilation and refrigeration should be started. Reefers ought to likewise be stacked in the boats as fast as these could really be expected. While stacking the boat, just as during ocean transport, temperature and ventilation levels should be looked after effectively. On landing in their destiny, palletized containers are quickly moved by street to ripening rooms and afterward to the wholesale dispersing specialist agents in America and Europe or somewhere else. 1.20 1.20.1

POSTHARVEST HANDLING AND STORAGE DEHANDLING

Dehandling is a process of making a gentle cut close to the stem with the help of clean and sharp banana knife. Not long after dehandling, the fruits are put with the crown confronting topsy-turvy onto a leafy layer for depleting the latex. To prevent the occurrence of crown disease, the hands are dipped in 0.1% solution of Benlate or Thiabendazole. 1.20.2

STOWING

Stowing is characterized as a course of action of banana packs in columns with the cut closures of pedicle confronting upward, expected to clear the spread of microbes conveyed from field in inactive condition or pervasive

46

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

under nearby local condition of storage. For the most part Stowing is carried out at two phases, first not long after harvest bunches are restowed in the field over a bed made of banana leaves and afterward they remain stowed in this condition still it is prepared for shipment in a carriage. This process of stowing is also recommended to follow even in transport and at the whole­ salers’ godown ahead of conveying to ripening room. 1.20.3 ARRANGEMENT OF PACKING Horizontal arrangement of fruits in the box is made, ideally, in two rows, with the crown end facing the box side and the fruit tips facing the middle of the box, which is said to be the safest place for safe shipping. However, for singlelayer packaging, it is best to keep the hands upright by holding the tips up and the crown down. In advanced state of packing to create modified atmosphere inside the box, practice of using cushioning pads or kraft paper at box’s bottom and covering of fruit with LDPE liner of 100 gauges should be followed. 1.20.4

PRECOOLING

Precooling assumes a huge part in expanding the storage life of the fruits, where the fruit is bound for the distant and export market. Following bunch harvesting within 10–12 h precooling of the produce ought to be done. Followed by precooling, bunches are subjected to forced air cooling for 6–8 h to bring back the fruit pulp temperature to 13°C from 30–35°C field temperature, at 85–90% RH. For storing reasons the crates ought to be promptly/immediately moved to cold rooms where the shelf-life of the produce could be expanded. 1.20.5

STORAGE

Guaranteeing the rules identified with harvest maturity of bananas could be exported effectively via ocean shipment. To accomplish this, storage conditions of 13°C and 85–95% relative humidity should be given. Failure of maintaining the storage temperature below 13°C leads to chilling injury followed by surface discoloration, dull color, uneven ripening, and browning of flesh of the fruit. Contingent upon the kind of cultivars, storage life at 13°C differs from 3 to 4 weeks or about a month. Low-temperature storage

Banana

47

combined with controlled environment storage shows correlative and complementary benefit for further extension of storage life. By keeping up proper controlled atmosphere storage condition of 5% O2 + 5% CO2 at 12°C to 13°C fruits of banana (cv. Robusta) could be stored for almost 2 months, in a green, unripe state. 1.20.6

RIPENING ROOM

To ensure proper ripening, green bananas are first placed into boxes or cushioned plastic crates at the optimal temperature. Any change in the prescribed temperature will harm the fruit during the forced ripening period. The ripening space should be locked, sealed, and airtight, with temperatures ranging from 16 to 180°C and humidity levels ranging from 85% to 90%. The temperature in the ripening chamber is regulated and managed using a thermostat. The ripening room should be supplied with ethylene gas at a concentration of 100 ppm (0.01%). Ethylene acts as a catalyst in the ripening process, kicking off the hormonal process needed for ripening. After 24 h, the ventilation port of the room should be opened to clear the ethylene gas and carbon dioxide emitted during the initial ripening process. After a closed 24 h treatment, the temperature of the ripening drops to 18°C and then steadily drops to 15°C for 3–4 days. 1.21

PROCESSING AND VALUE ADDITION

Bananas and plantains are cultivated in over 130 countries worldwide (in both tropics and subtropics); among them in some of the countries it is considered staple food crops. Countries such as India, Uganda, Brazil, and China, where bananas are consumed locally, do not have significant export opportunities (Pillay and Tripathi, 2007), but they experience huge loss due to improper storage and other marketing-related problems. There exists the opportunity to go for processing and value addition to tackle the postharvest loses. Among different processing options, most recent and must adopting technology may be the production of flour from ripe and unripe fruits and to mix the flour into various innovative processed products such as fiber-rich bread (Juarez-Garcia et al., 2006), cookies that can be digested easily (Aparicio-Saguilan et al., 2007), and fruit’s edible films (Sothornvit and Pitak, 2007). One of the most preferred by-products obtained from banana and plan­ tain is chips which has a widespread acceptability in many banana-growing

48

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

countries. In Bangladesh many fast food outlets use chips as their most popular snacks (Molla et al., 2009) and in Nigeria also banana chips get immense popularity (Onyejegbu and Olorunda, 1995). Aseptic canning is used to treat puree derived from ripe fruits of all banana varieties in which peeling, homogenization, centrifugation, air exhaustion, and lastly steriliza­ tion are the sequential steps to be carried out. After sterilization, the puree is packaged without contamination into vacuum-sterilized cans that are sealed in a steam environment (Sole, 1996, 2005). Another by-product resulting from fully ripe banana pulp is banana powder. Pulp is conveyed through a colloidal mill which converts the pulp into a finely grinded paste. To enhance the color of the final product an addi­ tion of approximately 1–2% potassium meta-bisulfite solution is advocated. Lastly, the solid recovery is performed through spray or drum drying of finely grinded pulp paste. Nowadays banana figs as a means of processed product gained huge consumer acceptability and are considered one of the best means of prolonging shelf life of banana. These banana figs were dried or dehydrated pulp having a fig-like sticky consistency and in taste it is on sweeter side. Originally, banana figs were created by sun drying in the tropics; recently hot air circulation in tunnel or cabinet dryers came up as the best means of drying. Banana flakes and purees are looking similar, but the flakes are prepared by drying the puree in large chrome-plated drum dryers. Among beverages wine, juice, etc. are also processed as value-added products. Bananas and plantains are commonly used as high-fiber sources, with the majority of the fiber concentrated in the dried petioles and leaf sheaths that comprise the pseudostem. Fiber yield ranges from 0.6% to 1.0% depending on the cultivar and method of extraction (Uma et al., 2002). In the main banana-producing countries, the production of starch from discarded bananas generates income side by side creating huge employment possibilities (Zhang et al., 2005). Unripe bananas are rich sources of starch and it quantifies up to 70–80% of its total dry weight (Guilbot and Mercier, 1985; Waliszewski et al., 2003). The starch content of banana is in equivalent range with the endosperm of corn and the flesh of white potato. 1.22

PEST, DISEASE, AND PHYSIOLOGICAL DISORDERS

Banana and plantain are vulnerable to a large extent of insect pests and pathogens. Some insect pests and pathogens are a bit serious and epidemic that can easily spread with the planting materials. After establishment, these

Banana

49

remain persistent and practically difficult to manage. There are several insect pests causing injury to the banana plants at various developmental periods of plant growth, thus reducing the yield potential of successful banana cultiva­ tion. Worldwide most prevalent pest and diseases of banana are described in the following tables along with their characteristic symptoms and remedial measure (Table 1.13 and 1.14). TABLE 1.13 Important Insects of Banana with Their Effective Control Measures. Pest

Characteristic symptoms

Management

References

Banana rhizome weevil (Cosmopolites sordidus Germar)

Larvae of the weevil first start its activity on damaging the rhizome and occasionally the pseudo stem. After hatching, the grubs bore into the rhizome by making tunnels where pupation occurs. During monsoon, plants become weak, ultimately rot and fall down

Addition of cover crop, inclusion of fallow in rotation sequences, mass trapping, use of biological control agents beside sucker treatment, and spraying and drenching around the base of the tree with Chlorpyriphos 20 EC (FP 2.5 mL/L) are the effective measures to control this pest

Gold et al. (2001), Tinzaara et al. (2005)

Giant banana stem borer Castniomera humboldti Boisduval and The banana stem weevil Odoiporus longicollis Olivier (quarantine pest of Australia)

Stem borer prefers to attack growing tip and kills seedlings and used to tunnel into standing corms and thus damages the corm tissue. Adult stem borer have characteristic nature of feeding on stem and suckers during night while remaining hidden during daytime. Plants that have been infected by the stem borer grow weak and finally decay

Avoidance of infested Pinese (1999), banana suckers; destruction Shankar et al. of places and structure made (2016) by the adult borers to hide or shelter; use of borer-resistant varieties like Basrai, Chitti, Kadali, Kunnan, Poovan, Poomkali, Sawaii, etc. for commercial cultivation; sucker treatment with Quinalphos emulsion (0.1%) or Chloropyriphos solution (0.05%) prior to planting and spraying of dimethoate 30 EC or Fenitrothion 50 EC @ 5 mL in 10 L of water around the base of the seedlings are some of the best integrated approach to escape weevil/borer problem in banana

50

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

TABLE 1.13

(Continued)

Pest

Characteristic symptoms

Management

References

Burrowing nematode (Radopholus similis)

Nematodes are well known for their destructive damaging ability on root and rhizome tissue. Damaged tissue becomes necrotic and plants are starved for water and nutrients uptake, become stunted with reducing bunch weights, that retards harvest. Severe damage declines the plant anchorage, which eventually results in plant toppling

Plantains in general are vulnerable, though some resistance can be found in dessert bananas such as ‘Silk’ and ‘Mysore’ groups along with few of the synthetic diploids of acumi­ nata such as H-59, H-65 and H-109. Application of nematicides (fenamiphos, fosthiazate, oxamyl) also recommended

Sarah (2000); Shankar et al. (2016)

Banana Thrips and Banana Tinged/ Lacewing bugs

Banana thrips and lacewing bugs develop almost similar type of characteristic symptoms. Both pests like to feed flower tips and fruit even prior to the bunch initiation and continue till 2 weeks after emergence. Infested fruit develops gray-brown roughening on the surface that ultimately turns corky and cracked at advanced maturity stage

As effective remedial Shankar et al. measures, embedding (2016) dichlorvos-impregnated plastic strips within the cover and removal of the male bud in earliest possible time may be done

Other pests of banana in different growing regions: Banana Moth—Opogona sacchari is native to Africa Peel-Scarring Beetles—Colaspis spp. Banana aphid—Pentalonia nigronervosa Coquerel Banana Fruit sucking Moth—Eudocima fullonia Fruit flies—Bactrocera musae Whitefly—Aleurodicus dispersus Russell Banana scab moth—Nacoleia octasema Sugarcane bud moth —Decadarchis flavistriata Walsingham Banana skipper—Erionota thrax L (Endemic to Papua New Guinea)

Banana

TABLE 1.14

51

Important Diseases of Banana with Their Effective Control Measures Fungal diseases

Disease

Symptoms

Management

References

Sigatoka diseases of banana (Causal organismMycosphaerella fijiensis (Black Sigatoka), M. musicola (Yellow sigatoka/Sigatoka)

Pale yellow streaks (Yellow Sigatoka) on upper leaf surface while lower surface witnesses the dark brown streaks in Black Sigatoka, each measuring 1–2 mm long, which overlaps to form necrotic lesions with light gray centers encircled with yellow halos

Remove the damaged plants and other debris, application of adequate nutrients, and good cultural practices like detrashing (deleafing); ensuring proper drainage and canopy aeration; resistant/tolerant culti­ vars are basic options to eradicate sigatoka disease. Chemically, it is controlled by application of prophylactic fungi­ cides like mancozeb or chlorothalonil combined with benzimidazole or triazole which have systemic action

Mourichon et al. (1997), Marin et al. (2003)

Fusarium wilt/Panama disease (Causal organism— Fusarium oxysporum Schlecht. f. sp. cubense (Foc).)

The fungus produce characteristic wilting symptoms by primarily infecting the roots of the plants, inhabiting in the vascular system of the rhizome and pseudostem within 5–6 months after planting, and the symptoms are observed both internally and externally. “Spiky” appearance of the plant with erect youngest leaves is one of the distinguishing characters of Fusarium wilt

Flooding which creates Stover (1962), Moore et al. anaerobic condition is successful in managing (1995) the disease at least for the first cycle of the crop Application of calcium compounds and phos­ phate to amend the soil for preventing growth of fungal inoculants Application of Bio control agents like, Trichoderma, Pseudomonas, Streptomyces, followed by nonpathogenic Fusarium (npFo) [both of endophytic and rhizospheric origin] are effective against Fusarium wilt

52

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

TABLE 1.14 (Continued) Bacterial diseases Disease

Symptoms

Banana Xanthomonas wilt, BXW (banana bacterial wilt-BBW). Also known as kiwatoka (Uganda) and Unyanjano wamigomba (Tanzania) caused by Xanthomonas campestris pathovar musacearum (Xcm)

As diagnostic symptom of bacterial wilt, yellowing and flaccidity on the oldest leaves, which later become necrotic and collapse at the base of the petiole is seen. Further, the characteristic symptoms are witnessing bacterial yellow ooze at vascular bundles and rusty brown spots in the pulp. Finally, the wilt affected pseudostems in progression of time commences death

Management

Practice of de-budding (removal of the male bud) is very effective in preventing the disease incidence since the incidence starts primarily from male bud. Introduction of Pflp and Hrap genes to East African bananas from sweet pepper using genetic engineering to Infected banana plants exhibit Moko diseases (including Bugtok) massive yellowing and wilting develop transgenic bananas resistant to caused by Ralstonia of leaves with vascular solanacearum discoloration in the pseudostem, BXW are in progress. In fields infested with leaf sheaths. Beside these, biovar 1, race 2 early fruit ripening or detained Xcm or Ralstonia, routine cleaning and fruit development, blackening sanitation practices of fruit, as well as fruit pulp should be followed dry rot are also observed as to disinfect garden/ characteristic symptom on field tools using moko affected banana plant a 20% solution of Discoloration and shattering Blood disease sodium hypochlorite (Indonesia) “Blood of the male flower bud and (NaOCl). Crop disease bacterium” peduncle is observed in rotation with velvet Ralstonia affected plant. When a bean (Mucuna (Ralstonia sp.) cut is made, it causes a reddish pruriens) for one or identified strain staining of vascular tissue all Ralstonia syzygii two cycles has been subsp. celebesensis over the plant, resulting in effectively imple­ reddish-brown bacterial ooze. mented to reduce Here the damaged plant's older R. solanacearum leaves become yellow, followed count in the soil by withering, necrosis and of badly affected ultimately the plants collapse. banana farms in While, younger leaves get Costa Rica. Dazomet bright yellow color before (Basamid®granular becoming necrotic and dry 97%) is an alternate soil sterilizer that effectively controls Moko/Bugtok disease

References Ploetz et al. (2003), Biruma et al. (2007), Blomme et al. (2017)

Banana

TABLE 1.14

53

(Continued) Viral diseases

Disease

Symptoms

Banana Streak Virus (BSV)—first reported on Musa (AAA group Cavendish subgroup) “Poyo” from Cote d’ Ivoire

Necrotic streaks and periodical expression of symptoms are key identity of BSV. Most isolates produced discontinuous or occasionally continuous chlorotic or yellow dots or streaks which become necrotic, run from the midrib to the leaf margin

Management

A strict quarantine and certification program for banana planting materials is one of the prerequisite to combat the impact of viral diseases on banana industries. Eradicating the Development of intermittent, Bunchy top virus episomal form of disease (BBTV)— dark green dots and streaks of first reported in Fiji varied length on the leaf sheath, BSV using antiviral compounds such as petiole, veins, and midrib are and subsequently in Taiwan at about visible characteristic symptom adefovir, tenofovir, and 9-(2-phosphono­ 1900 and Egypt in excepting few cultivars. methoxyethyl)­ Emerging leaves of affected 1901 2,6-diaminopurine plant are shorter in length, brittle in texture, and narrow. In (PMEDAP) has been reported infected plants flower produc­ tion is disrupted and if bunches Two recently devel­ are formed due to late infection, oped banana cvs. fingers developed in those “Tinawagan Pula” bunches not reach to maturity and “Tangongon” Foremost observable symptom through gamma Banana bract irradiation mediated of this virus infection is mosaic virus vitro mutagenesis production of spindle-shaped, (BBrMV), a showed putative pinkish to reddish streaks potyvirus, of the resistance to BBrMV. family Potyviridae, on the midrib, peduncle and Wild and unattended pseudostem. Similar spindle was discovered shaped streaks along with mild patches of banana in the Philippine prescribed to remove island of Mindanao. mosaic streaks have also been to lower the popula­ observed on bracts, peduncle, tion density of causal and fingers. In some cultivars vectors. Application (like Nendran), characteristic symptom developed as leaf with of herbicides, such as fernoxone or 2,4-D, altered orientation giving the appearance of “Traveler’s Palm along with systemic (Ravenala madagascariensis), insecticides, has been recommended to kill having spindle-shaped mosaic the infected plants patterns on both upper and and to prevent the lower leaf surfaces. spread of vector from the treated plants

References Selvarajan et al. (2007), Magnaye and Espino (1990); Robson et al. (2007), Helliot et al. (2003); Tripathi et al. (2016)

54

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

1.22.1

PHYSIOLOGICAL DISORDERS

1.22.1.1 CHOKE THROAT If severe low temperature prevails for longer time, it affects bunch forma­ tion and results in improper bunch emergence. As in this case, the distal part of inflorescence comes out and the basal portion becomes shrinking at throat. It is called choke throat. In this situation leaf yellowing first occurs and under adverse conditions the leaves turn necrotic. Here, an extended bunch maturity period of 5–6 months than normal 3.5–4 months has been observed. These symptoms are more or less similar for November dump which develops mostly at the prevalence of certain extreme low tempera­ tures ( Pb > Cu > Ni > As > Cd > Hg which yielded fruit which are containing heavy metals, such as Zn > Cu > Ni > Cr > Pb > As > Cd > Hg. A positive correlation in Zn, Cu, Ni, and Pb content and a negative correlation in Zn, Cu, Ni, and Pb content between fruit and soil were observed. Heavy metals content of the tested soil and fruit samples as evaluated by single pollution index and comprehensive pollution index method is in a safe limit and satisfies all safety standards. This also indicates that the tested citrus orchards can develop pollution-free citrus devoid of any residual metals. Panigrahi et al. (2017) studied for 7 years on the effect of surface soil run off came to the conclusion that runoff of the top fertile soil in rainy season followed by a lower soil water content in the root zone of plants during post-rainy period is one of the major causes for low citrus productivity and a significant decline of citrus orchards in tropical and subtropical regions. They adopted varied rainwater conservation techniques (RCTs) and studied their long-term effects on the nutrient loss and yield of citrus orchard. Adop­ tion of staggered trench (ST) and continuous trench (CT) with and without grass mulch (GM) was effective in conserving rainwater, soil, and nutrients (N, P, K, Fe, Mn, Cu and Zn). This positively influenced the vegetative growth, leaf nutrient content, fruit yield, and fruit quality of citrus plants. Available nutrients and organic carbon content in soil were significantly improved in mulched plots. They concluded that the integrated utilization of CT and GM was successful enough to reduce rainfall runoff, reduced soil nutrient leaching. This resulted in higher yield. The water use efficiency was also improved by adopting such standard practices (Panigrahi et al., 2017). The effect of low pH was observed on Citrus sinensis and Citrus grandis based on concentrations of nutrient elements in root, stem, and leaf. Seedling growth, leaf gas exchange, pigment concentration, ribulose-1,5-bispho­ sphate carboxylase/oxygenase activity and chlorophyll a fluorescence, relative water content, total soluble protein level, and H2O2 production and

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

electrolyte leakage in roots and leaves were also observed. pH 2.5 signifi­ cantly suppressed seedling growth and numerous physiological parameters were transformed. pH 3 somewhat inhibited seedling growth. pH 4 had virtu­ ally no impact on seedling growth. Seedling growth and many physiological parameters attained their maximum at pH 5 with negligible seedling death. H+ toxicity unswervingly served mutilation to citrus roots, affected the uptake of mineral nutrients and water, diminished the uptake of nitrogen, calcium, potassium, phosphorus, and magnesium. Leaf CO2 assimilation was affected, diminished photosynthetic ETS augmented creation of ROS. Mottled bleached leaves lacking enough chlorophyll occurred in C. grandis seedlings. Mandarin was slightly more tolerant to H+ toxicity than pummelo (Long et al., 2017). In a study conducted by Tubiello et al. (2002) by using two different GCM scenarios in the United States, the total citrus production increased significantly due to climate change. The overall citrus yields increased by 20–50%, whereas the use of irrigation water decreased as well. Total crop loss due to freezing condition was projected to be lowered by 65% in 2030 and 80% lower in 2090. Iglesias et al. also projected that citrus crop is least affected by changing climate scenario while conducting research trial in different locations of Spain. 2.11

PROPAGATION AND ROOTSTOCK

Citrus is a broad group of plants consisting of several species. Different species have different methods of propagation. Budding is also an impor­ tant method of propagation of citrus. Different species of citrus responds to different rootstock in a different manner. Even different variety of same species has different need of rootstock. Budding is practiced in the case of sweet orange and grape fruit. Acid lime, sour lime, Mexican lime, Rangpur lime, and Kagzi lime is propagated by seeds. Sweet lime or Indian lime and Tahiti lime is propagated by ground layering/air layering. Pummelo is commercially propagated by air layering and T-budding. Air layering is also practiced in the case of limes and mandarins (Barlass and Skene, 1986). 2.11.1

SEEDS

Seeds are the major tools for propagation in lime. Seed propagation is the most ancient and natural mode of propagation. The advantage with

Citrus

111

polyembryonic species of citrus is that the nucellar seedlings obtained by sexual reproduction are true to the type to that of the mother plant (Iglesias et al., 1974). It is of utmost importance that zygotic seedlings must be identi­ fied on the basis of morphology in the earlier stage only and removed from the uniform nucellar seedlings. This would help to maintain clonal unifor­ mity. Fresh and disease-free fruits are harvested from the tree and seeds are extracted from it. The seeds are recalcitrant in nature and should be planted very soon after extraction. Seeds are sown in the month of May–June and September–October. Seeds germinate in 15–20 days after sowing. In next 30 days, a pair of leaves emerge out. After 2–3 months, seedlings with a pair of leaves is planted in raised bed as nursery. 2.11.2 AIR LAYERING Air layering is adopted as a commercial method of propagation in pummelo, limes, and mandarins. For air layering to be done successfully, a stem is selected with sufficient carbohydrate reserve and the thickness of the stem should be more than that of a pencil. Then the outer bark and phloem is removed but the cambium is kept intact. Later, the layered portion is tied with sphagnum moss and wrapped with polythene. After 1–2 weeks, roots are developed from the layered part. The portion is cut and is planted to obtain a plant which is true to the type healthy plant. In this nursery stage, only the lesser vigorous and nonuniform sexual seedlings are eliminated. After 1–2 years, when the seedlings are 40–60 cm tall, then they are transplanted to open field condition. 2.11.3

BUDDING

It is a method of budding in which an incision is made on the rootstock and a healthy bud is inserted in it. The bud is tied and is allowed to form association with the rootstock. After that the composite plant is allowed to grow. Citrus is propagated by T-budding and shield budding. T-budding is a method of propagation mainly followed in mandarin. Pummelo and grape fruits are also propagated by T-budding. This is done in the season when the sap flow is low in the month of May–June and October– December. The bud that would be inserted should be free from chimera and sports, have good vigor and free from latent viruses. The mother plant from which bud is extracted is needed to be indexed for potential disease threat by tristeza, mycoplasma, psorosis, and exocortis.

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

2.11.3.1 RAISING OF ROOTSTOCK FOR GRAFTING AND BUDDING Rootstock is raised just like the traditional method of seed propagation. Rootstock is chosen very judiciously and ensured that the rootstock not only induces desirable qualities but also make the plant system resistant to several biotic and abiotic stresses. Commonly used citrus rootstock and resistant rootstock are listed in Table 2.25 and 2.26. Xu et al. (2017) observed that grafting significantly affected the expression of microRNAs and their target genes in both scions and rootstocks. In the scion, grafting augmented the expression of microRNAs and repressed those target genes expression responsible for plant growth and development, stress response, and hormone signal transduction. In the rootstock, grafting suppressed the expression of mi-RNAs related to the increased vigor of rootstock, improvement in root growth and development, and a better stress response. Candidatus Liberibacter asiaticus is responsible for the cause of citrus huanglongbing disease (citrus greening). This was reduced by leaf-disc grafting which is a new method of grafting in which a disc of leaf tissue is replaced with a similar disc from a diseased plant. This is done in young plants which are less than 1 years old (Zambon et al., 2017). Balal et al. (2017) compared the effects of chromium (Cr) toxicity on the photosynthesis rate, antioxidants, biomass development, reactive oxygen species, and nutrient concentration in Kinnow mandarin plants when they are grafted on diploids (2×) and tetraploids (4×) of P. trifoliata [L.], Citrus reshni, and C. limonia Osbeck, respectively. The kinnow mandarin plants which were grafted on tetraploid (4×) rootstocks exhibited significantly extraordinary tolerance to chromium toxicity. The tetraploid rootstock plants maintained a superior biomass gathering and less reduction in the overall photosynthetic activity, stomatal conductance, transpiration rate, water use efficiency, and activities of antioxidant enzymes. Tetraploid plants showed a lesser lipid peroxidation and lesser formation of reactive oxygen species. Neither does it affect the plant absorbance of Ca, Mg, P nor K. the presence of chromium was higher in roots but was not allowed to get translocated in the stem. QingPing et al. (2017) evaluated eight rootstocks for their resistance and tolerance toward acidity and alkaline in South China. Shiikuwasha, Shantou Suanju, and Ni 8047 exhibited inordinate tolerance to acidic soil (pH: 3.5) whereas Niedu Yeju and Daoxian Yeju were susceptible to acidic soil. “Goutou” sour orange, Zhuju, and Shiikuwasha overcame good suppleness

Citrus

113

toward alkaline condition. Niedu Yeju and Daoxian Yeju were sensitive to higher pH in the soil. Among all, Shiikuwasha exhibited improved toler­ ance to both acidic and alkaline pH and have an outstanding potential to be used as rootstock for breeding material. XiaoKe et al. (2017) studied about a new rootstock C. junos known as “Pujiang Xiangcheng” in China. This species showed high early fruiting, stabilized yield, resistant to cold, tolerant to alkaline soil. It is very tall and strong with resistance to cold and frost. McCollum and Bowman (2017) while evaluating the rootstock for Ray Ruby grapefruit found that Sour Orange and citrumelo when employed as a rootstock yielded the largest fruit while US-897 (semi-dwarfing rootstock) yielded the smallest sized fruit. Peel thickness was more in the case of sweet orange as rootstock. TSS was observed maximum in “US-897” and the least in x639 and US-852. US-942 and US-897 rootstock gave the best quality fruit when used as rootstock with grapefruit. TABLE 2.25 Rootstock Seldom Used in Budding (Anon, 2019). Sl. No.

Plant

Rootstock Preferred

Reason of Preference

1.

Citrus group

Adajamir (C. assamensis)

Resistant to greening

2.

Lime and lemon

P. trifoliata (Trifoliate orange) Resistant to cold, dwarf in nature, resistant to Phytophthora, resistant to tristeza and nematode

3.

Lime and lemon

C. unshiu (Japanese mandarin) Resistant to freezing condition

4.

Lime and lemon

Rangpur lime (C. limonium)

5.

Lemon var. Verna Sour orange

6.

Lime and lemon

Rough lemon (C. jimbiri)

Resistant to tristeza virus, saline condition

7.

Sweet orange

Citron (C. medica)

Resistant to citrus canker

8.

Mosambi

Rangpur lime

–

9.

Satgudi

Rough lemon (C. jimbiri)

–

10.

Blood red

Karna khatta

–

11.

Mandarin

Troyer citrange

HDP (1.8 × 1.8 m)

12.

Mandarin

Rangpur lime

–

13.

Grapefruit

Troyer citrange

Dwarf

14.

Grapefruit

Oroblanco

High TSS and optimum acidity in organic system

Vigorous and hardy Drought tolerant and Regulated Deficit Irrigation (RDI)

Jatti khatta

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

TABLE 2.25

(Continued)

Sl. No.

Plant

Rootstock Preferred

Reason of Preference

15.

Mandarin

Cleopatra mandarin

Tolerant to tristeza, exocortis, and xyloporosis

16.

Sweet orange, mandarin, and lemon

Sour orange (C. aurantium)

Cold-hardy

17.

Orange and mandarin

African Shaddock × Rubidoux – trifoliate

18.

Orange and mandarin

Benton citrange

19. Orange and mandarin

–

P. trifoliata × C. sinensis Borneo Red

Tolerance to the tristeza virus and resistance to soil-borne diseases

20.

Orange and mandarin

Bitters C-22 citrandarin (Citrus sunki)

Less susceptible to granulation, tolerant to Phytophthora para­ sitica, can grow in calcareous soil and good tolerant to viruses

21.

Lemon and orange

Carpenter C-54 citrandarin

Less susceptible to granulation, tolerant to freezing, slightly tolerant to P. parasitica, can grow well in calcareous soil and good tolerant to viruses

22.

Lime, Lemon, and orange

Furr C-57 citrandarin

Plant is tolerant to tristeza virus, somewhat tolerant to Phytophthora sp., and can grow in calcareous soil

23.

Lime, Lemon, and orange

C-32 citrange trifoliate hybrid

Low seed count

24.

Sweet orange

Citradia hybrid (CRC 1437)

Cold and frost tolerant

Citradia hybrid (CRC 1438) 25. Sweet orange 26.

Grapefruit seedling

Goutoucheng sour orange

The fruits are tristeza resistant and salt tolerant

Grapefruit seedling (CRC 343) High-yielding, cold-hardy and somewhat virus tolerant

Citrus

115

TABLE 2.25

(Continued)

Sl. No.

Plant

Rootstock Preferred

Reason of Preference

27.

Orange and mandarin

Rusk citrange

Cold-hardy and somewhat nematode tolerant

28.

Orange

Seville sour orange

Resistant to the tristeza virus

TABLE 2.26

Rootstock Resistant/Tolerant to Diseases and Stress.

Sl. No. Rough lime Trifoliate orange Sour orange Sweet orange Rangpur lime Sweet lime Cleopatra mandarin Troyer citrange Grapefruit

Exocortis T S T T S S T

Gummosis S T T S T T T

S T

T S

Xyloporosis Nematode Tristeza T S T T T T T S S T S T S S T S S S T S T T T

S S

T S

Salt T S T T T T T T S

T—Tolerant. S—Susceptible.

2.11.4

MICROPROPAGATION OF CITRUS

Micropropagation is a very fast, reliant, and rapid multiplication technique that is seldom used in citrus. Propagation by traditional method is slow and is huge time-oriented and rapid rate of multiplication is not possible. Citrus is also highly affected by virus and other latent microbes. There is also a huge demand of true to the type and genuine planting material. Considering these factors, micropropagation seems to be the best method of propaga­ tion. Micropropagation ensures rapid production of clean and clonal plants (Chaturvedi, 1979). Micropropagation involves the production of clean and clone plants through techniques, such as shoot meristem culture and micrografting (Parthasarathy et al., 2001). Citrus production in orchards is steadily declining due to spread of virus infection (Chaturvey et al., 2001). Huge number of diseases in citrus are due to virus and virus-like organism that enters due to the use of affected bud wood and stock (Roistacher, 1991).

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Spain is one such country which has obtained its world dominance in citrus production and quality by adopting micropropagated citrus plants (Navarro and Juarez, 1977; Navarro, 1992). 2.11.4.1 SOMATIC EMBRYOGENESIS Many viruses which are affecting citrus orchards can be eliminated success­ fully by somatic embryogenesis (D’Onghia et al., 2001). Somatic embryogenesis is another highly tried propagation technique in citrus. Somatic embryogenesis from either embryos or ovular tissues has been expansively explored in citrus. Maheshwari and Rangaswamy (1958) was the first to report in vitro regeneration of embryos from the nucellus cultures. Hidaka et al. (1981) successfully regenerated diploid (2n) plants from anthers of sour orange. Gill et al. (1995) achieved somatic embryos from cotyledon, epicotyl, root, and leaf segments of in vitro grown nucellar seedlings of mandarin. Nito and Iwamasa (1990) obtained somatic embryos from cultures derived from satsuma juice vesicles. Six different Citrus species exhibited embryogenic potential from cultures of pistil transverse cell layer explants (Carimi et al., 1999). Carimi et al. (1994, 1995) established embryogenic cultures from stigmas and styles of grapefruit, lemon, mandarin, sweet orange, and sour orange. 2.11.4.2 SHOOT-TIP GRAFTING/MICROGRAFTING Citrus is often seriously affected by diseases caused due to viroids, viruses, bacteria, and phytoplasma (Roistacher et al., 1976). Since citrus orchard is a matter of long-term investment, its economic losses are very alarming. This badly affects the overall longevity, productivity, and vigor of the orchards. The book entitled “Improvement of shoot-tip grafting in vitro for production of virus-free citrus” by Navarro et al. (1975) came out to be the stepping stone for all research related to shoot-tip grafting. Shoot-tip grafting or micrografting is the most common method of large-scale production of healthy citrus plant. It is done simply by placing a small shoot tip obtained from a new flush on a plant (0.1–0.2 mm from top to bottom) in the presence of a stereomicroscope under aseptic conditions. The excised apical dome is inserted in inverted T structure. The graft union is comparatively much early. The composite plant thus obtained comes to bearing much early and is free from any graft-transmissible pathogen

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(Murashige et al., 1972). This method is mandatory if citrus germplasm is to be exported in foreign countries. Even the pathogens which cannot be heat-killed can be removed by this technique. The resultant healthy plant thus produced attains the vegetative stage just as the mother plant. Hence, the resultant plant has no juvenile characteristics and attains reproductive stage very early. The resultant plant is indexed to check if it is pathogen-free. Steps involved in shoot-tip grafting are the following: Step 1: Selection of mother trees from the local cultivars. Step 2: Obtaining in vitro rootstocks (sexual seedling). Step 3: Sources of flushes for shoot tips. Step 4: Rootstock preparation from seeds. Step 5: Isolating the scion and performing the graft. Step 6: Care of in vitro STG plants (27°C for 16 h). Step 7: Transfer of shoot-tip grafted plants to external environmental conditions after 4th–6th week. Step 8: Maintenance. A complete eradication of tristeza, psorosis, cristacortis, infectious varie­ gation, concave gum, impietratura, cachexia, and exocortis was obtained when micrografting is done using thin-layered cell of stigma and style culture (D’Onghia et al., 2000; Fiore et al., 2002). Nakajima et al. (2017) success­ fully eradicated three viroids (Hop stunt viroid—HSVd, Citrus dwarfing viroid—CDVd, and Citrus viroid VI—CVd-VI) from the plant system by utilizing 0.2 mm long shoot tips of Satsuma mandarin var. Miekinansangou by shoot-tip grafting or micrografting. 2.11.4.3 MICROBUDDING Budding is a very popular technique of citrus propagation which requires proper contact between the tissues of scion and root stock, meristematic growth, and a favorable environment. Microbudding is a very unpretentious, economical budding practice which was first developed by Dr. M. Skaria, Texas A&M University, USA. In Nagpur mandarin, it was also standardized (Vijayakumari and Singh, 2003; Vijayakumari et al., 2008). At Central Citrus Research Institute, the plants developed by microbudding produced vigorous, disease-free, marketable budded plants. Budding was done on 5–6-month­ old root stocks in a very shorter duration. Unlike traditional budding system, microbudding ensures rapid and year-round propagation. For the first time in India, Citrus reticulata Blanco var. Nagpur Mandarin was budded on a

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5-month-old rootstocks at CCRI. With the help of this technique, a huge number of healthy planting materials can be developed at a very cheap and affordable rate. 2.12

LAYOUT AND PLANTING

Citrus includes a wide number of species and each species will have a diverse group of subspecies. Even there is huge variation in the size and shape of different varieties of the same species. This is the main reason why the spacing between plant to plant and row to row is very much fluctu­ ating and also depends on the variety selected, the rootstock vigor, and the soil type. Basically, square and rectangular layout of planting is followed. Citrus orchard is a matter of long-term investment and hence judicious planning and layout is very necessary to be done. Usually, square system of layout is preferred in the case of citrus. A pit of 60 cm × 60 cm × 60 cm is dug. The pit is filled up with 10–12 kg FYM and soil. 10% BHC powder can also be added to reduce ants, mites, and termites. Micronutrients, such as zinc, iron, manganese, and copper can be added @25 g/pit if soil is exhausted of micronutrients. For most of the sweet orange varieties, a spacing of 6 m × 6 m is maintained between plant to plant and row to wow. In case satgudi seedling is used, the spacing of 7.5 × 7.5 m is maintained. For Pummelo, spacing of 5 m × 5 m is kept. For lime and lemon, in the case of non-dwarfing rootstock row to row spacing of 3–4 m and plant to plant spacing of 3 m is kept. If Mosambi variety is budded or grafted on Rangpur lime, planting distance is kept to 6 m × 6 m. In another practice, citrus is planted at a distance of 3×3 m or 4×4 m which is increased to 6 m × 6 m to 8 m × 8 m by thinning out the extra trees in between as the plant vigor increases over year. A study was conducted by Nishikawa et al. (2017) to study the effect of plastic mesh as ground cover and planting bed height on flowering and fruit production in grapefruit orchard (3 months old). Expression of a flowering-related gene (CiFT) was observed in stem tissues. CiFT2 gene expression was significantly enhanced in trees planted in raised beds without any ground cover. The tree grown in raised beds with ground cover was less with CiFT expression. Trees which were planted in raised beds without any ground cover produced significantly more inflorescences per node than those trees grown in any type of beds with ground cover (Nishikawa et al., 2017). HDP of citrus can exponentially improve the productivity of citrus. Little endeavor toward selection of proper pruning practices, optimizing the

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ideal planting distance, adoption of dwarf rootstocks (troyer citrange, assam lemon, trifoliate orange) and the use of plant growth retardants (Paclobutrazol and GA3), reducing excess application of nitrogen-based fertilizers are needed. Thus, citrus cultivation in traditional density can accommodate 440 trees/ha, 952 trees/ha for double-row planting and 600 trees/ha for standard row planting. HDP ensures higher net returns, growing values per unit land, competent use of soil moisture and other agronomic advantages. The only constrains in HDP is light availability and nutrient competition which can be overcome by adopting ideal management practice. Japanese dwarf citrus cultivars are planted at 2.74 m × 2.74 m for HDP. Kinnow planted at 2 m × 2 m produces 200% more yield than normal planting (Singh and Singh, 2018). Troyer citrange can be planted at 1 m × 1 m for achieving a very high yield (Shrestha, 2010). Other reports of HDP in orange are 1.0 m × 3.3 m (Wheaton et al., 1994) and 3.5 m × 1.5 m (Bordas et al., 2012). 2.13

IRRIGATION

Citrus group is known to respond very luxuriantly to supplementary irriga­ tion. Citrus fruit contains a high amount of water and the rate of transpiration is also high as compared with other fruits. So, it gives better result when the orchard is irrigated. The sap circulation is very high in citrus which is attributed to the high-water demand of the fruit. Citrus is an evergreen tree and hence the rate of moisture loss is also higher as compared with deciduous ones. During critical stages of fruit set, fruit growth and develop­ ment, if there is moisture stress, then it might affect the crop qualitatively and quantitatively as well. A citrus tree needs 1200–1500 mm water annually. A major part of this is obtained through rainfall, however, the remaining water is needed to be provided through irrigation. At pea-sized stage, fruits need irrigation without which fruit drop may occur. The amount of supplementary irrigation however depends on the climate, the soil type, variety, and the root depth. Nagpur mandarin growing in black soil of Maharashtra would require less water as compared with Khasi mandarin in Meghalaya. In summer months, irrigation is desirable after every 7–10 days interval but irrigation is not needed in rainy seasons. Stagnation of water near the tree trunk in case of sweet orange and mandarin can be detrimental and induce Phytophthora rot. Irrigation is done by ring basin system. However, the ring basin system is also desirable to reduce water contact with the stem. Drip irrigation can also be useful but is of high instal­ lation cost, but is useful in soil with high infiltration rate. Ring basin method

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

of irrigation is very popular in areas where water availability is abundant and other systems, such as drip and sprinkler are very hard to install. Drip and microjet irrigation system are very much feasible in areas where the land is slanted and uniform wetting of soil surface is needed. Moreover, drip irrigation is much more profitable than the traditional methods of irrigation (Shirgure et al., 2003). Rondey et al. (1977) found higher tree vigor and less water wastage in Valencia orange under drip irrigation which was grown in sandy soil. Similar observation was recorded by Simpson (1978) that there is a move from flood and furrow irrigation to better systems like microjets and drip irrigation. Slack et al. (1978) established that drip system of irrigation on juvenile orange orchard used only 5400 L of water compared with enor­ mous 23,400 L of water per tree in the case of traditional systems. Scuderi and Raciti (1978) observed a higher yield, weight per fruit, and improved quality in Valencia orange under drip irrigation as compared with non-trickle modes of irrigation. Similar observations were also drawn by Tashbe et al. (1986). Microjet sprinkler irrigation also have become popular because of its water use efficiency and low-budget application in Nagpur mandarin. It was observed that maximum fruit yield was optimized in microjet 1800 (Fanjet) which was 40.33 t/ha followed by 2700 microjet (Rayjet) which was 39.89 t/ha. Highest TSS (10.12°Brix) and juice content (43.05%) was observed in plants which used microjet 1800 (Fanjet) irrigation (Shirgure et al., 2002). Panigrahi et al. (2017) studied the effect of enhanced irrigation through drip irrigation and flood basin irrigation and nutrient application in over­ coming low productivity and decline of mandarin productivity of citrus orchard in vertisol soil of Central India. Drip irrigation treatments with 75% and 100% class A pan evaporation rate along with 75% and 100% of recommended fertilizer dose (N:P2O5:K2O = 600 g:200 g:100 g) were applied. Highest fruit yield (16.39 t/ha), water use efficiency (3.9 kg/m3), and fertilizer use efficiency (87.3 kg/kg) were observed in 75% class A pan evaporation rate and 75% of recommended fertilizer dose. In the same treat­ ment, concentrations of N, K, and Fe in leaves, leaf water use efficiency were significantly higher. 100% class A pan evaporation rate and 100% of recommended fertilizer dose resulted in highest rate of leaf photosynthesis, stomata conductance, and transpiration (Panigrahi and Srivastava, 2017). Several methods of microirrigation are known to us which have enough potential to replace the traditional method of irrigation and reduce water wastage. System that supports fertigation along with irrigation is also attaining enormous importance.

Citrus

2.14

121

NUTRIENT MANAGEMENT

Optimum availability of nutrients in available form to plants is ensured by the application of manures and fertilizers. Fertilizer requirement of citrus is largely dependent on age, variety, cultivar, rootstock used, soil type, etc. In double-ring system of planting, fertilizer is applied on the ring at a distance of 120–150 cm from the trunk. This is the zone where maximum feeder roots are available. A 12–15 years old citrus tree has a well-developed root system. Every plant should receive a supply of 10–15 g of well-rotten farm yard manure per year. 450 g Nitrogen and 900 g of potassium and phosphorus can be very useful. Nitrogen and potassium should be supplied in split doses. The major nutrients are easily available to the plant through common fertilizers but the micronutrients are actually the factors that determine the ultimate quality of the fruits. Micronutrients like Zinc (Zn), Iron (Fe), Calcium (Ca), Boron (B) and manganese (Mn) if applied to citrus would improve the flow­ ering and fruit quality. A spray of 0.5% zinc (Zn), 0.3% copper (Cu), 0.2% manganese (Mn), 0.2% magnesium (Mg), 0.1% boron (B), and 0.2% ferrous sulfate (Fe) can provide all desirable nutrients to the plant. A micronutrient mixture pack can ensure high yield and quality. Silva et al. (2017) evaluated the residues of citrus for available nutrients, macronutrients and micronutrients, such as Ca, Fe, Mg, etc. An average of 25.64 g/100 g carbohydrates, 6.09 g/100 g protein, 9.53 g/100 g moisture, 3.23 g/100 g ash, 3.15 g/100 g lipids, 34.26 g/100 g insoluble fiber, and 27.88 g/100 g soluble fiber were present. The percentage of dialyzable minerals and soluble ranged from 5.59 to 69.06% and from 19.36 to 77.33% for Fe, from 14.71% to 26.13% and 33.34% to 60.84% for Ca, and from 34.42 to 62.51% and 29.95 to 94.20% for Mg, respectively (Silva et al., 2017). Davinder et al. (2017) studied on the influence of boron (B) and zinc (Zn) on growth, yield, and overall quality of Kinnow grown in Punjab. It was observed that a treatment of B and Zn (250 g/plant) gives number of fruits (269.66), fruit weight (198.78 g), weight of fruit/plant (58.00 kg), and vitamin C (20.83%), fruit drop (33.21%). In foliar dose with treatment of Zn @3 g and B @2 gm gives more fruits (298), improves plant height (25.40 cm), weight of fruit/plant (60.00 kg), and vitamin C (17.50%). When both basal dose and foliar application was repeated with same dose, plant height (29.46 cm), fruit length (4.95 cm), width (5.61 cm), and vitamin C (24.16%) should show significant improvement. The lowest fruit drop of 28.48% was obtained in this combination of treatment. When C. sinensis and C. grandis were subjected to boron toxicity (400 µM) for 15 weeks, it was observed that C. sinensis was more B-toxicity tolerant than C. grandis. C. sinensis roots

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

had an improved capacity to retain cell wall structure, fight against ROS, ensure correct protein formation and maintains cytoskeleton integrity than C. grandis roots (Wen et al., 2017). Citrus orchard productivity is believed to be optimum only in the case when the nutrient is supplied based on the leaf and soil nutrient guide. High production in 1 year yielding small-sized fruits is undesirable as compared with average amount of production with good quality (Srivastava and Singh, 2004). This is achieved by soil and leaf nutrient analysis in which the soil sample and leaf sample is analyzed to optimize the amount of nutrients needed. This is also known as critical leaf nutrient standards. This varies from region to region and place to place depending on how much the soil has been exploited and whether the soil is virgin or exploited. In India, N (2.91–3.15%), K (1.51–1.61%) and Mg (0.32–0.36%) is recommended for Coorg mandarin in South India. An ideal value of 2.8%, 0.15%, 1.57%, 0.34%, 103 ppm, 38 ppm, 62 ppm, 9.8 ppm, and 109 ppm of N, P, K, S, Fe, Mn, Cu, and Zn was recommended for Kinnow in Northern and Western India (Chahill et al., 1991). N, P, K, Ca, Mg for optimum fruit yield was observed in Coorg mandarin which was 2.77–2.79%, 0.14–0.16%, 1.48–1.56%, 1.49–2.41%, and 3.57–3.81%, respectively (Bhargava and Singh, 2001). In Nagpur mandarin, optimum leaf nutrient level was 2.24–2.4% N, 0.07–0.10% P, 1.18–1.56% K, 1.32– 1.55% Ca, 0.48–0.67% Mg, 110.24–132.12 ppm Fe, 29.36–43.41 ppm Mn, 8.26– 14.07 ppm Cu, and 18.60–29.80 ppm Zn (Kohli et al., 2016). Sweet orange type mosambi grown in Western India needs N @2.36%, P @0.13%, K @1.62%, Ca @2.65%, Mg @0.32%, Fe @132ppm, Mn @112.4 ppm, Cu @6.8ppm, and B @29.4ppm (Srivastava and Singh, 2002). 2.15 TRAINING AND PRUNING Citrus does not need a drastic training or pruning. But indeed, it can improve productivity and fruit quality. Usually, citrus tree is trained in single-stem system where only a single branch is allowed to emerge out. Any second branch is not allowed to grow. After the first year of planting, the plant should not be allowed to grow above 0.75–1.0 m. Anything above this height should be chopped down. This is known as heading back. This promotes the development of side shoot. In coming second year, 4–6 main branches all around the main trunk are allowed to develop. These branches should have perfect angle with the main trunk. The angle between developing branches should not be too less that the light penetration is less neither should be too much that it breaks apart. In the third year, the 4–6 surrounding branches are

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allowed to grow up to a height of 2–3 m. Then it is trained for the penulti­ mate time. The tree is ready and further training is not required. This is the foundation to a strong canopy. Pruning of citrus is a very important operation that determines the overall quality. Pruning is needed to be done right from pre-bearing stage till the plants have potential to flower and fruit. In bearing stages it must be ensured that the diseased and dead branches are nipped off time to time. The criss-crossed or overlapping branches are also needed to be chopped off. It must be ensured from time to time that no branch or vegetative shoot is allowed to grow below the bud union. The water sprouts and suckers developing from rootstock are needed to be removed regularly. Thinning of excess branches and vegetative shoots are necessary for good light penetration. Removal of excess branches would balance the C:N ratio and improve the flower development, fruit set, and overall productivity. Pruning is done in late winter or early spring just after harvesting of the fruits. After pruning, Bordeaux paste is applied to avoid fungal infections. Besides, fruit thinning and flower thinning can improve the fruit quality and improve biochemical attributes. Rouse et al. (2017) studied the effect of severe pruning and enhanced foliar nutritional treatments on rehabilitation of Huanglongbing (HLB)/ greening affected citrus trees and the quality of fruits that are produced on the basis of yield, growth, and juice quality. Usually, the HLB/greening affected plants are stunted, weak, diminished, show dieback symptoms, and are poor in production. The 15-year old “Valencia orange” on citrumelo with 100% occurrence of greening were pruned back to the main scaffold branches. After that both pruned and non-pruned were subjected to nutrient application. The pruned trees had higher chlorophyll content (per cm2 leaf area) than non-pruned ones. The fruit yield in terms of quantity was higher in non-pruned ones for 3–5 years but in later days, the pruned trees showed better results in terms of yield. 2.16

INTERCROPPING

Citrus, like mandarin, sweet orange, pummelo, and grape fruit usually takes 5–7 years to come to full shape. Lemon and lime take at least 4–5 years to come to full-yield stage. Before that they neither cover full canopy nor do they provide enough income to the grower. In the meanwhile, intercrop can be useful for income generation and for the purpose of utilizing the unutilized space. Intercropping with short duration crop like tomato and legumes like

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

peas, beans can help to get good income during rabi season. At kharif season, planting of cowpea, gourds, and lady’s finger can be very good option. 2.17 WEED MANAGEMENT Weeds can prove to be detrimental in citrus field. It can affect the yield adversely and reduce the overall quality of the fruits. Weeds, such as Convol­ vulus arvensis, Cyperus rotundas; Cynodon dactylon, Sorghum halepense, Diacanthium annulatum, Eragrostis minor, Andropogon sp, Fumaria purvi­ folia, Tribulus terrestris, Sonchus arvensis, Euphorbia thumbifolia, Cromophus didimus, Amaranthus viridis, Euphorbia microphylla, Vicia sativa, etc. are predominant in citrus field. Their management is needed so that they do not affect the yield and quality adversely. The weeds serve as serious competitor for nutrients, space, and water as well. Sweet orange is the citrus crop which is highly affected by weed infestation. The management of weed below a danger level is of utmost importance. Weed management in citrus can be done using hand hoe or tractor drawn harrow in the case of large orchard. Chemical control of weed can also be done in the case of high weed infestation. Application of preemergent and postemergent herbicide can be very effective. Diuron is a preemergent weedicide when sprayed @3 kg/ha twice at 120th day and 240th day can prove to be control weeds upto 280–300 days. For preemergent control, application of 2,4-D @5 kg/ha in 500 L water followed by 2.5 kg paraquat in 500 L water is applied at 30 days interval for 6 months. Bromacil is an effec­ tive weedicide for sweet orange. Glyphosate is effective against weeds, such as Panicum maximum, Cyperus rotundas, and Cynodon dactylon upto 5–6 months. Simazine and atrazine control weeds very successfully in sweet orange. In a study by Martinelli et al. (2017), it was found that ruzi grass (Brachi­ aria ruziziensis) when used as a sod grass (cover crop) in Tahiti lime orchard and were subjected to ecological mowing gave the best result in terms of yield quantity and weed management efficiency. This non-glyphosate system significantly reduced glyphosate entry in the crop system as well. 2.18 2.18.1

FLOWERING, POLLINATION, AND FRUIT SET FLOWERING

Most of the citrus species produce flowers during spring months and when favorable temperature and soil moisture are available. Many acid group citrus

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125

species, such as acid lime, lemon, and citron flowers almost throughout the year. Under south Indian conditions, citrus flowers several times indistinctly in two to three seasons in a year because there is no well-defined winter and summer seasons. In North India, almost all citrus species flower during February–March after completion of low temperature winter stress when the temperature rises and soil moisture improved (Hayes, 1970). Instead of taking three poor crops, growers adopting only one growing season (bahar) in the tropical and subtropical regions of India. There are three bahar cultivation regulated such as ambe bahar, mrig bahar, and hasth bahar (Table 2.27). In the Central and Western India, the flowering occurs during in the month of February known as ambe bahar and gives the main crop in the month of November–December. Flowering in July is known as mrig bahar and the harvesting of this crop done in March–May. The fruits harvested in the mrig bahar fetch higher price in the market and this bahar is mainly preferred in the area where water is scarce in May–June and preferably fruits being too acidic and raw and this crop escapes from the fruit-sucking moth infestation. The flowering obtained in the October month is called as hasth bahar and harvesting of this crop is done in July–August. As compared with other bahar cultivation, the yield is lesser in hasth bahar. In Central India, the bahar treatment is followed and it includes several cultural practices such as withholding the irrigation for 2 months before flowering in order to create artificial stress condi­ tions in Nagpur mandarin (Citrus reticulata). If the leaves are not wilted or fallen on the ground, then growers normally remove the soil up to depth of 10–15cm thereby expose the tree roots by slight root pruning at one side of the canopy. The pit is filled after 10 days with mixture of soil, FYM, and sand in equal proportion and subsequently light irrigation is given at weekly interval. This practice ensures tree to flower profusely instead of entering to vegetative flush. This practice is not followed for September–October flowering crop in Central India, North India, and also in tropical regions of South India where the rainfall frequently occurs, however, these practices are not holding good for these regions. Several practices performed in the subtropical India for encouraging the flowering in citrus, such as with­ holding irrigation, exposing roots by slight root pruning, use of specific growth regulators, and also by fruit thinning with the use of chemicals. The greater accumulation of low temperature about 11–15°C increases the floral intensity with maximum number of flowers per flowering bud. A higher winter low temperature greatly reduces the flowering intensity in the “Valencia” and “Hamlin” oranges under Florida condition (Valiente and Albrigo, 2004). The higher level of IAA in the leaves enhances the

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flower bud formation of the Satsuma mandarin (C. unshiu) but at higher concentration of GA1/3 in the leaves reduces the flower bud formation when the tree is under water stress condition. Thirugnanavel et al. (2007) demonstrated that delaying the flowering in the acid lime can be achieved by applying GA3 (50 ppm) in June and subsequently Cycocel (1000 ppm) in September and finally KNO3 (2%) in October showed greater effect in reducing the number of flowering shoots and initial fruit set. The other growth regulators include CCC, SADH, ethrel, and BOA also are involved in the promotion of flowering in many citrus species. In the USA, sweet orange variety “Pineapple” starts flowering in the middle of January and a variety Washington Naval orange produces flowers during early spring in Australia, but the same variety flowers during early January in Japan. In the Indian condition, Blood Red and Jaffa varieties produce flowers at the end of January. Flowering in citrus species occurs in varying period of the year and it largely depends on the locality and prevailing weather conditions. TABLE 2.27 Different Bahars and the Seasons. Bahar

Month

Season

Ambe bahar

February–March

Early spring

Mrig bahar

June–July

Rainy season

Hasta/Hatti bahar

September–October

Autumn

2.18.1.1 MECHANISM OF CITRUS FLOWERING IN DIFFERENT WAYS 2.18.1.1.1 Flowering in Relation to Nitrogen Assimilation The flowering behavior in citrus is well-demonstrated in the world through Kraus-Kraybill hypothesis. This hypothesis is an internation­ ally recognized, which gives the precise idea about the role of balanced ratio of carbohydrate and nitrogen in the stimulation of citrus flowering. The higher the ratio of carbohydrate/nitrogen in the plant results in the enhanced flowering, whereas lower ratio of C/N alters the plant toward vegetative growth. The two-hypothesis proposed by Lovatt et al. (1988) in citrus flowering indicated that (1) the rise in the ammonia accumula­ tion because of an enhanced biosynthesis of arginine and polyamine in the plants under stress condition, However, these changes could cause the rapid

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cell division when the tree become free from the stress. Another hypothesis describes that all these physiological changes and following rapid cell divi­ sion in the plant are the prerequisites for citrus flowering. Kato (1986) and Mooney and Richardson (1992) demonstrated that more than 80% of N is derived from reserved N during the growth of new spring flush and in fruit set period. However, changes in the leaf NH3+–NH4+ content during stress situations was well-studied in citrus. In addition to the above information, the studies conducted by Huchche et al. (1996) in Nagpur mandarin in the Central India reported that there is no relation between the leaf content NH3+–NH4+ and the flowering intensity. But later, they only demonstrated that leaf NH3+–NH4+ content is vital indicator during stress for the induc­ tion of flowering in Nagpur mandarin. The enhanced accumulation of leaf NH3+–NH4+ and biosynthesis of de novo arginine occurred in response to many abiotic stresses. The several nitrogenous compounds accumulated during stress conditions, such as proline, glycine, betaine, and putrescine, etc. but not clear their role in the flowering promotion. 2.18.1.1.2 Flowering in Relation to Carbohydrate Metabolism The balanced ratio of carbohydrate and nitrogen is an essential for obtaining the best flowering in citrus was well accepted by Kraus and Kraybill hypothesis. The girdling treatment on the main stem and branches induces the flower forma­ tion by accumulating the carbohydrates at girdled place. Lovatt et al. (1988) demonstrated that the threshold level of starch and ammonia are both crucial for most citrus flowering and on the other side, the lower level of gibberellins are the prerequisite for the promotion of flowering in citrus (Goldschmidt and Monselise, 1972; Guardiola et al., 1982). This shows the dominant regulatory role of carbohydrates in the nutrient diversion of flowering hypothesis (Sachs and Hackett, 1983). The lack of minimum level of starch in the tree during offyear causes the alternate bearing in the citrus as a result no flower formation in the off-year. The decreased level of starch content in the leaves not only reduces the intensity of flowering but also suppresses the growth of new shoot formation and feeder root development. The heavy fruit load during on-year in “Murcott” tree is one of the major reasons for the carbohydrate’s starvation at root zone in the following off-year. However, there is no any new shoot and new feeder root development because of nutrient deficiency. Therefore, the sufficient level of carbohydrate in the leaves is critical for citrus flowering to overcome the alternate bearing problems.

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2.18.1.1.3 Citrus Flowering Using Growth Regulators The citrus flowering can be greatly controlled by an exogenous application of permissible phytohormones. The flowering manipulation in the preferred bahar could be possible by the use of specific plant growth regulators (PGRs). The studies on endogenous effect of PGRs is not yet clear where the effect of an exogenous application is well-established in the induction of citrus flowering. An application of MH at concentration up to 200 ppm increases the length of dormant period. The PGRs, such as NAA, MH, 2,4,5-T, and ethephon are found to be effective in thinning out of fruits, thereby enhancing ethylene formation. 2.18.1.1.4 Growth Retardant—Paclobutrazol (PP333) The paclobutrazol is one of the effective growth retardants in perennial fruit crops to overcome the alternate bearing problem. The soil application of PP333 at a concentration of 1–5 gram per tree for two consecutive years, then increased flower intensity was observed in the next following season in sweet orange, Nagpur mandarin, and satsuma mandarin. This growth retardant plays a significant role in decreased GA biosynthesis in tree, however, reduced internodal length and shoot length. In some conditions, PP333 is unable to promote flowering in citrus because of heavy fruit load which is beyond the cultivar­ dependent threshold level (Martinez-Fuentes et al., 2013). The roots contain the higher level of PP333 content as compared with surrounding soil root zone and which would be used in the up-coming flowering seasons. 2.18.1.1.5 Alternate Bearing Control Alternate bearing is the most common problem in the perennial fruit crops due to carbohydrate starvation, nutrient deficiency, and poor supply of photoassimilates happened in the off-year. The obtaining optimum or heavy yield in the on-year and lesser or no yield in the following off-year is known as alternate bearing and this clearly shows the simultaneous fruit development and inhibition of vegetative growth in the on-year. During off-year, tree itself recover from deficient stresses and maintain its physiological stability for the successful fruit production in the succeeding on-year. Obtaining optimum yield in all the seasons is possible only by manipulating the physiological activity of the tree. The exogenous application of PP333 through soil drench

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and foliar spray was found to be effective for flower manipulation in the chosen bahar. The soil application of PP333 (5 g/tree) is effective than foliar spray. The foliar spray of PP333 (500 ppm) would be carried out only under severe problem of alternate bearing. 2.18.2

POLLINATION

Citrus is highly a cross-pollinated fruit crop and it is most commonly performed by an insect honey bee. Under solid plantation, most of the citrus species are self-pollinated. In citrus, both self- and cross-incompatibility and both male and female sterility are reported. The flowers are hermaphrodite and their stigma is remaining receptive for 6–8 days. A cross-pollination is so common in the mixed planting of different cultivars. Cross-pollination is essential for seediness in several varieties, such as Shamouti and Jaffa oranges, clementine and Nagpur mandarin, and Minneola tangerine. The seedless parthenocarpy fruits are formed after the cross-pollination in the varieties, such as Marsh and Thompson seedless grapefruit. Nagpur mandarin shows both self- and cross-compatibility with all varieties except with grapefruit (Kedar and Gopal Krishna, 1977). The varieties Washington naval, Satsuma mandarin, and Tahiti lime (Bears lime) show the strong male sterility, whereas female sterility is more distinct in the lemon varieties, such as Lisbon and Eureka and also in Marsh grapefruit. The partial incompatibility is also found in Orlando tangelo, Siamese Pummelo, sweet lime, Nepali Oblong, Italior, and Luknow seedless lemon, etc. The successful fruit production of Kagzi Kalan lemon needs a 10% pummelo trees as pollinizer. The planting of Italian and Nepali Oblong lemon as pollinizer for Pant lemon-1 variety. The variety Pineapple sweet orange and Duncan grapefruit acts as pollinizer for sweet lime. Therefore, the sufficient placement of beehives and planting of suitable pollinizers in the orchard is essential for proper pollination and fertilization of flowers in order to obtain the successful fruit production. 2.18.3

FRUIT SET

In fruit crops, fruit setting is mainly affected by several factors, including abiotic stresses (high temperature, drought, salinity, and fluctuation of soil moisture) and biotic stresses (pathogens, insect pest, mites, and nematodes). Generally, the fruit set percentage is calculated as the percent of the last number of fruits retained on the trees to the first flower number. Fahad and

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Rab (2014) demonstrated that an improved fruit set and controlled fruit drop in sweet orange cultivars Mosambi, Blood Red, and Succari obtained by the application of GA3 at a concentration of 30 ppm at blooming stage. The fruit set in the citrus is basically triggered by auxin through modulating the GA metabolism as a result of marked changes in the GA1 level in pericarp and ovules (Bermejo et al., 2018). Girdling after 35 DAA in the high-bearing cultivar “Clausellina” Satsuma mandarin shows increased fruit set percentage and final fruit yield (28%) and in the case of low-bearing cultivar “Fortune” mandarin, girdling at 15 days before anthesis to 35 DAA was found most effective in increasing the fruit yield by 125% (Rivas et al., 2006). This girdling practice does not affect the level of soluble solid content and final fruit size. Arunadevi (2019) reported that the application of PP333 (1.5 g ai/m2) with combination of NAA (200 ppm) increases the fruit set percentage, fruit retention percentage, and yield per tree in the acid lime (Citrus aurantifolia) variety PKM1 as compared with the control trees. The application of GA3 during initial fruit growth causes the development of undesirable fruit quality and also the formation of fruits having less juicy with rough and thick skin. Therefore, application of right plant hormones at right stages with specific known quantity is crucial for successive fruit setting in fruit crops. In a study conducted by Ferrer et al. (2017), it was observed that Benzyladenine (BA) encourages cell division, growth and development in presence of optimum endogenous auxin concentrations. BA when applied after flowering, increased the fruit set and fruit size in Tangor cv. Murcott. BA was applied in different concentration 30 ppm, 60 ppm, 90 ppm, and control at time of anthesis. A significant increase in size and number of peri­ carp cells were observed. Massive cell division was observed in central axis and locules because of which larger sized fruits were found. A significant increase in the number of fruits retained were observed. 2.19

FRUIT GROWTH AND DEVELOPMENT

The fruit growth and development in the citrus groups from fruit set to harvest has found a single sigmoid growth curve. The citrus fruit develop­ ment consists of two slow growth periods with one rapid growth period in between. Fruits are non-climacteric with respect to maturity, however, harvested fruits could not show any respiration upsurge and ethylene accumulation. Therefore, these citrus fruits are ripened only on the tree.

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Normally, citrus fruits take 6–18 months for full growth and development from citrus flower ovary to fruit ready to harvest stage. Citrus fruit growth and quality are largely depending upon the type of fruit, specific cultivar, type of soil and climate, water availability, nutrient supply, and cultural practices. Rebolledo et al. (2012) reported that the application of 2,4-D at a concentration of 20 mg/L (i.e., 3.6 L/tree) in sweet orange. var. Salustiana increases the fruit growth rate and fruit size after 53 days of anthesis due to increased rate of cell expansion of juice sacs, however, the number of fruits per tree is reduced, but there is no impact on the total fruit yield per tree. The “Kinnow” mandarin tree sprayed with 0.6% zinc sulfate increases the better fruit diameter, fruit weight, total phenol, and ascorbic acid content as compared with all other treatments (Razzaq et al., 2013). Mai et al. (2014) reported that there are four growth curves in new pomelo cultivar Guiyou No.1 such as slow growth, rapid growth, steady growth, and ceased growth. The fastest growth is occurring in June. However, peak increment in both vertical and horizontal diameter of the fruit is appearing between May and July. Shireen et al. (2018) revealed that an application of NAA at the rate of 200 mg/L after June drop enhances the fruit size, fruit weight, TSS, and juice percentage in the Kinnow mandarin. This study shows that use NAA as fruit thinning agent for reducing the crop load. 2.20 2.20.1

FRUIT RETENTION AND FRUIT DROP DIFFERENT PHASES OF FRUIT DROP

The fruit drop in citrus occurs in different period and at the different stages of fruit growth. Several factors are responsible for the fruit drop, such as physiological causes, biotic, and abiotic stresses. The biotic stresses include pathogens, insects, and nematodes. However, fruit drop by abiotic stresses includes extreme salinity, drought and higher temperature, and rainfall. Therefore, the fruit drop in citrus is classified into three ways: (1) Post-setting drop: It is the first phase of fruit drop which occurs soon after fruit set as a result of over fruit setting. Later, the citrus tree itself sheds the fruitlets and thereby keeps up the balance. The fruit drop at this stage is not of much concern to the growers. (2) June or summer drop: Citrus fruits drop in the northern hemisphere generally occurs during the months of May–June in the hotter periods while fruits’ drop during November–December occurs intermittently

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in the southern hemisphere. Fruits’ drop during summer months is so common in the high temperature arid regions though, this summer drop has not affected severely on the total yield. This shows that tree balances its source and sinks relationship. (3) Preharvest drop: The mature fruits drop from the tree before the harvest. This drop is considered as economic importance to growers. The fruits drop during this phase causes the greater loss to the growers thereby resulting in reduced total yield. 2.20.2

FACTORS RESPONSIBLE FOR FRUIT DROP

(1) Physiological drop: The fruitlets drop at the early stage of devel­ opment after fruit setting indicates physiological adjustment to the several stresses, such as high temperature, drought, and water deficit. However, the fruitlets drop is more severe at higher temperature (35–40°C) during June, this incident is known as June drop or summer drop in the northern hemisphere and the same incident happened in November in the southern hemisphere. An internal adjustment of tree physiology keeps the number of fruitlets according to available source. (2) Entomological drop: Several devastating insects, including fruitsucking moth (Otheris fullonica and O. materna) and fruit fly (Daucus dorsalis) cause greater infestation to ripening fruits. Many insects act as vector for many diseases, such citrus mealy bug, aphids, citrus psylla, citrus butterfly, and leaf minor cause direct and indirect infestation thereby an increased fruit drop occurs. Apart from these, a noninsect pest like citrus bud mite also is responsible for the heavy drop of flowers and fruits in the citrus species thereby reducing the final yield due to falling of an infested fruit before the harvest (Randhawa and Dhillon, 1965). (3) Pathological drop: The fruit drop in citrus also occurs due to the infection of fungi, bacteria, virus, and nematodes. Fruit rot disease caused by many fungi, such as Phytophthora nicotianae, P. palmivora, P. citrophthora, Colletotrichum gloeosporioides, and Botrydiplodia theobromae results in falling of matured and semiripened fruits before harvest. Fagan (1979) reported that postbloom fruit drop is a serious disease caused by Co. gleosporioides in sweet orange at Belize, Central America. The bacterial diseases, such as

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greening and canker affect the fruit yield extremely, and in addition to these, viral diseases, such as tristeza, xyloporosis, porosis causes reduced fruit yield. The citrus nematode and burrowing nematode infestation also are responsible for fruits drop in citrus orchard. 2.20.3

STRATEGIES FOR CONTROL OF FRUIT DROP

Fruit drop in each citrus growing region can be controlled through adopting good agricultural practices, such as time of application and right concentra­ tion of plant hormones should be worked out for successful management. Some plant hormones are most commonly used for controlling the fruit drops, namely, 2,4-D, 2, 4,5-T, NAA, GA3, CIPA An application of 2, 4-D at a concentration of 60 ppm during June reduces the preharvest fruit drop significantly (Amiri et al., 2012). Ghosh et al. (2012) stated that application of NAA at 15 ppm was found effective in the control of fruit drop in sweet orange. Ashraf et al. (2012) recommended that the application of Zn+ K+ SA (0.25% ZnSO4 + 0.25% K2SO4 + Salicylic acid 10 μM) combination during onset of flowering, fruit formation, and at the stage of color initiation of fruit in “Kinnow” mandarin. However, percentage fruit drop was reduced by 30% with increased fruit juice quality, ascorbic acid, TSS, and fruit yield. One of the major pathogens Colletotrichum acutatum causes the postbloom fruit drop (PFD) in most of the citrus group varieties, as a result, it affects flowers and causes early fruit drop. This pathogen infection can be controlled with the application of Bacillus subtilis-based formulations with talc as a carrier and in addition to that nitrogen source is also supplemented. In field conditions 73% asymptomatic citrus flowers were obtained (Klein et al., 2016). The use of NAA (20 ppm) and GA3 (30 ppm) controls the fruit drop significantly and increases the fruit size, length and weight of sweet orange cultivar “Jaffa” (Sweety and Reddy, 2018). The physiological drop can be decreased by the use of synthetic auxins like NAA and 2,4-D at right time with known concentration. The insect pest can be controlled by adopting the poison baiting technique which includes a mixture of Malathion (20g) + jaggery (200g) + some vinegar or fruit juice in 2 L of water has been used for successful measures for minimizing the preharvest fruit drop. The control of fruit-sucking moth is always a challenging task for growers, therefore, different colored insect traps can be used for controlling the sucking pest, such as mealy bug, thrips, aphids. Fruit fly population is mainly controlled by timely use of baiting technique. The pathological drop can be reduced by

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the use of systemic fungicides, such as Bavistin and benomyl. Therefore, practicing the integrated nutrient management, integrated pest and disease management is the key element for successful citrus fruit cultivation. An application of 2,4-D at a concentration of 60 ppm during June reduces the preharvest fruit drop significantly (Amiri et al., 2012). Ghosh et al. (2012) reported that application of NAA at 15 ppm was found to be effective in the control of fruit drop in sweet orange. 2.21

HARVESTING AND YIELD

Harvesting should be done judiciously as the oil gland in the skin does not get ruptured. Citrus is best when harvesting is done by hand with care and adore. But hand harvesting in the case of bigger orchards or thorny orchards might be very cost-ineffective. In the case of tree citrus, such as pummelo and grape fruit, it shall be ensured that harvesting is done mechanically with utmost possible care. Very often, it has been observed that during the process of mechanical harvesting, the citrus oil gland gets ruptured due to the impact of fruits with the collecting surface (Glancey and Kee, 2005). Optimization of vibrating/shaking speed and pattern of shaking was also standardized by Whitney et al. (2000). According to them, linear vibration of the trees reduces mechanical damage of the tree branches and barks with a frequency of 7 Hz for 5–10 s. According to Torregrosa et al. (2009) 72% of fruits were detached in the case of heavy tractor shaker and 57% in the case of hand-held shaker for 5–7 s. If the fruit falls on the ground, rotting and decay would be much earlier. Hence, it is advised to use net or cushion while harvesting the fruits. In an experiment conducted by Ortiz et al. (2011), it was revealed that dropping of fruits in weeds, mulching material, or in shock absorbing canvases significantly absorbed higher amount of shock than the bare earth. Elevated canvas with wheel and frames was found to be the best possible way to mechanically reduce fruit injury during harvesting. The application of trunk shaker and cushion to harvest citrus was found to be more than 20% cheap than the use of mechanical harvesting (Brown, 2005). As citrus is a highly non-climacteric fruit, so its quality and flavor does not improve after harvesting. Therefore, harvesting in optimum maturity is of utmost importance. Citrus, like lime and lemon, is harvested when the juice content is maximum and the fruit attains perfect maturity and desirable size. In orange, mandarin, pummelo, and grape fruit, harvesting is done at ripe conditions. This is the stage when fruit attains attractive color and acceptable

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sugar: acid blend. Sweet orange matures in 9–12 months but can be allowed to remain on the tree for several weeks without spoilage. Tree storage is not advised in regions where granulation and fruit-sucking moth is a problem. In India harvesting season for sweet orange is December–February (North India), October–March (South India), December– March (East and North Eastern India). In Western India, harvesting of sweet orange is done during November–January (Ambe bahar) and March–May (Mrig bahar). Fruits are not needed to be pulled and are harvested using a secateur. Pummelo is known to show fruiting in all three bahar including ambe bahar, mrig bahar, and hasta bahar. Average yield potential described in Table 2.28. TABLE 2.28 Average Yield Potential of Citrus Groups. Sl. Crop No.

Average Age (in years)

Average yield

Maximum Average Fruiting Possible Yield Per Tree Per Year (in kg)

1.

Lime

8–0

–

3000–6000 fruits/year

1000–2000

2.

Lemon

8–10

–

–

600–800

3.

Sweet orange

10–20

7500–10,000 kg/ha

17,000 kg/ha

1000

4.

Mandarin

10–20

8000–12,000 kg/ha

25,000 kg/ha

4000

5.

Grapefruit

8–15

400–600

6.

Pummelo

10–25

200–500

2.22

POSTHARVEST TECHNOLOGY

Postharvest loss in the citrus group of fruits ranges from 15% to 30% due to several factors, including rough mechanical handling, poor management, and microbial decay. While transporting the fruits to different market places, the spoilage reached to an extent of 30%. Citrus skin is very much leathery and hence it is comparatively a less perishable fruit when compared with other fruit crops, including loquat, lychee, fig, and mango (Kader and Arparia, 2002). But nowadays due to mishandling and bad postharvest practices, the orchardists and fruit sellers are facing a considerably huge postharvest loss. The main reason behind the loss is due to rough and indecorous handling during the process of harvesting, precooling, handling, storage, transporta­ tion, and marketing. As a result, if improper handling is practiced, bruises and injuries are common in the fruit. This results in various maladies, decay, and physiological disorders during storage and marketing chain. Citrus

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strictly is a non-climacteric fruit and hence there is no rise in endogenous and exogenous ethylene production, and subsequent increase in the rate of respiration. However, if the fruit is subjected to endogenous ethylene or exogenously applied ethylene, it may have serious impacts on the fruit shelf life and overall quality attributes (Porat et al., 1999). To minimize the loss and to improve its overall postharvest system, it is very important to understand the nature of the fruit, its botany, the enzymes present in it, and various other factors affecting the overall postharvest shelf life. Citrus is rich in vitamin and minerals which are required for the human health, and it is also an important source for vitamin C, antioxidants, and phenolic compounds. Citrus fruits are very important raw material for the processing industry, and the value-added products made of citrus have great demand in the world market and trade. Fruit shelf life is influenced largely by relative humidity, vapor pressure deficit, temperature movement, composition of gases, bruises, and presence of microbial inoculum (Murata, 2001). The most important factors affecting postharvest shelf life and quality include root stock used, cultivar chosen, cultural practices adopted, harvest efficiency, precooling type, and various fruit treatments and storage conditions. 2.23 POSTHARVEST MANAGEMENT PRACTICES 2.23.1 WASHING After harvesting, it must be ensured that the fruits are washed methodically so as to remove the surface dirt, prevailing microorganisms. It also means subjecting the cuticle and oil gland to breathe and respire properly. Tradi­ tionally, fruits are washed in two steps initially in running water and then with 2% chlorinated water. Washing can also be done mechanically. The washing system consists of properly revolving the fruits with cylindrical shaped brushes, and washing with spray nozzles. At the distal part of the washer, a foamy solution of food compatible detergent is salivated on the fruit flavedo. The brush almost revolves at a speed of about 100 rpm which brushes the fruit thoroughly. It is important to screen the duration of the scrubber, depending on the mechanical strength and thickness of the peel. A washing time of 20–30 s is adequate for mandarin, sweet orange, lime, and lemon. However, pummelo and grapefruit can be washed for 30–40 s as well. Excessive brushing time can cause external damage to the fruit which is known as “brush burn.” After the fruits are subjected to foam washing, the fruits are thoroughly rinsed and cleaned with clean water sprayed from

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tiny nozzles. For add on benefits, the fruits can be sprayed with preservative solution like sodium orthophenyl phenate (SOPP). 2.23.2

DRYING

Partial drying of the flavedo can do a whole lot good to the overall fruit quality and shelf life. Citrus surface drying is one of the most critical operations in the packing house. If moisture is removed from the surface of the skin, it creates an impermeable layer for microorganisms to penetrate. However, the temperature of the drying air and duration of the drying process are the important factors in drying. A high temperature for longer duration might cause damage to the albedo. Extreme air temperature or extending the drying period may cause impairment of quality and shorten the shelf life (Fito et al., 2004). 2.23.3

CURING

Curing is a major maneuver to reconcile the wounds and induce the resistance to various infections. Some commonly used methods involved in curing for citrus are thermal curing. In this process, the citrus fruits are subjected to 2–3 days to a temperature higher than 30°C at a considerably high relative humidity (>90%). Hence, we can term curing as an endeavor by which a significant number of wounds are healed and resisted microbial infection after exposure to hot air (Ben-Yehoshua and Porat, 2005). In another way, the hot water tumbling of citrus fruits for 2–5 min at 45–55°C has reducing incidence of postharvest pests and diseases. Significant decline in molds were clearly observed (Hong et al., 2007). Hot water dipping is the tech­ nology which is easier, cheaper, and more practicable for heat application. This is because, water is much more an efficient heat transfer medium than air (Wang et al., 2001). 2.23.4

DEGREENING

Green colored fruit is not desirable in the case of citrus. To obtain a noteworthy market price, the external appearance of the fruit is of great important. Aesthetic appearance of fruits only attracts the consumer. Most of the consumers like dark colored fruit instead of lighter colored ones. With maturity, the citrus fruits loss their chlorophyll and gradually

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gain carotenoids. But chances of not losing the green chlorophyll are also there. The color development of the outer flavedo (rind) depends largely on climatic factors. It was observed that when a temperature below 4°C is maintained, the greatest increase in carotenoids occur in Valencia oranges (Young and Erickson, 1961). Exposing the harvested fruits to exogenous ethylene persuaded un-embellished physiological variations mostly destruc­ tion of chlorophyll pigment, synthesis and increase of carotenoids (Rodrigo and Zacarias, 2007). The color of the fruit flavedo changes from green to the characteristic color of each species. However, if the duration of contact with ethylene is prolonged and the concentration of ethylene is high, then undesir­ able effects may occur (Saltveit, 1999). This would adversely reduce the shelf life of the citrus fruits. Postharvest degreening of citrus fruit is done in degreening chambers. The effective concentration of ethrel for postharvest degreening of citrus fruit ranges from 1000–5000 ppm, depending on the cultivar. Higher concentrations above 5000 ppm depress degreening with rind injury. 2.23.5 WAXING The main purpose of waxing is to ensure that the fruit comes in lesser contact with the air. As lesser contact is there with oxygen, the rate of respiration is also reduced. During washing, the natural wax coating of the fruit is lost. This is to be upregulated by some external application. Waxing prevents the loss of moisture and keeps the fruit juicy and fresh for long period. It also provides a barrier to gas exchange and provides a support for preserving agents. The commercial waxes, such as carnauba, gum arabic, gum traga­ canth, gum acacia, and shellac are generally used. Resin and composite waxes, for example, polysaccharide and shellac—beeswax, and vegetable oils are being researched for their effects on shelf life and fruit quality. Polymer like corn starch is also used. In mandarins, resin and shellac solu­ tions substantially reduced the rate of pitting (Dou et al., 2000). In India, after harvesting, kinnow fruits were subjected to waxing and another set of fruits were not waxed. At higher percentage, physiological disorder was observed in unwaxed fruits along with a higher biochemical loss (Dinesh et al., 2002). Haider et al. (2017) studied on the effect of different edible coating on Kinnow and its impact on the shelf life and other biochemical attributes. It was observed that paraffin and sharine wax exhibited minimum lower weight loss (11.87%) and lower incident of fruit rot (2%) even after 90 days

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of storage. The minimum changes in weight, TSS/TA ratio, juice content, ascorbic acid, peel/pulp ratio, and sugar contents were recorded in coated fruits. Wax coatings retained a higher level of antioxidant (63.4%), total phenolics (240.7 mg GAE 100 g−1), and enzyme activities during storage. 2.23.6

PACKAGING

Packaging is an important aspect as this determines the overall quality and marketability. Selection of packaging materials is product-specific and also depends on the market demand of the fruit. For packaging of fruit like pummelo with a thick rind and lesser market demand as compared with sweet orange for which generally cheap packaging material is used. Expensive citrus-like sweet orange can be packed using modified atmosphere techniques and using different types of packaging materials. Besides, proper cushioning materials, such as paper, polythene sheet lining, individual shrink polythene cardboard boxes covered high- and low-density polyethylene, wrapping or seal packing can be employed (Ei-Mughrabi, 1999). Lemons and grapefruit can be packed in low-density polyethylene or high-density polyethylene bags and stored at 8°C for 3 months. Seal-packed citrus significantly showed reduced incidence of chilling injury and decay. The total soluble solid content or acidity of the fruit was not significantly affected (Ismail and Ei-Menshawy, 1997). In an experiment using different packaging materials, that is, plastic (20 µm) wrapping, plastic (20 µm) with 5 holes wrapping, plastic (20 µm) with 10 holes wrapping, newspaper wrapping, and jute wrapping. Among the various packaging materials, plastic (20 µm) with 5 holes wrapping was found to be effective in improving shelf life, minimizing weight loss, slow change in color, index, lower pathological disorder, and higher marketability (Bhattarai and Shah, 2017). For long distance transportation, cardboard boxes, wooden boxes, and crates can be used. 2.23.7

STORAGE

Citrus is a very delicate fruit. Citrus is also not found throughout the year, so there is lot of emphasis on citrus storage. Quite amazingly, citrus can be stored on tree even after attaining full maturity. However, the duration of tree storage varies with cultivars and changing climate. In the case of postharvest storage, mandarins stay well at 5–8°C, whereas oranges at 4–8°C with relative humidity of 90–95% (Kader and Arparia, 2002). Fruits

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could also be stored at low oxygen concentration (3–6%) and carbon dioxide concentration (2.5–4%) for more than 5 months (Sun and Sun, 1998). Controlled atmosphere storage is not advocated as the technique is too costly for moderate-valued fruit crop like citrus. 2.23.8

OTHER POSTHARVEST TECHNIQUES

Ascorbic acid content is an important factor for postharvest quality. Fruits with a higher amount of vitamin C would help in providing the desirable component in human diet. The content of vitamin C in citrus is prejudiced by several preharvest aspects including the soil type, the weather during fruit harvesting, genotype used, cultural practices adopted, harvesting maturity, and postharvest practices followed (Magwaza et al., 2017). Vera-Guzman et al. (2017) studied on the consequence of application of pectic oligosac­ charides (POs) and galacturonic acid oligosaccharides (GAOs) in reducing postharvest peel pitting (NCPP), decay, and chilling injury (CI) in orange cv. Navelina and cv. Rio Red. It was observed that POs presented a healthier effectiveness than GAOs in mitigating postharvest losses in orange. The POs were able to reduce NCPP and decay in grapefruit stored at 20°C. Applica­ tion of 10 g/L POs reduced CI and the chilling-induced ethylene production in oranges and grapefruits. Loss in organic acids during fruit ripening and storage is a predominant factor responsible for reduction in fruit quality and market value. γ-aminobutyric acid (GABA) serves as an important compo­ nent in citrate metabolism and improve citric acid longevity. Amino acids, such as alanine, glutamate, aspartate, serine and proline were also increased on γ-aminobutyric acid application. The application of GABA downregulated antioxidant enzymes, reduced ATP wastage and prevented fruit rot (Sheng et al., 2017). Penicillium digitatum and Penicillium italicum are microbes respon­ sible for postharvest green mold and blue mold in citrus. H2O2–Ag+ postharvest application at concentration of 1%–20 mg/L significantly reduced microbial population without affecting color and other important attributes (Zheng et al., 2017). Ornelas-Paz et al. (2017) observed the effect of gamma-irradiation (150, 400, and 1000 Gy) on the postharvest quality of Citrus kinokuni mukakukishu. It was observed that irradia­ tion at 400 and 1000 Gy reduced fruit firmness, sugar content, vitamin E, carotenoids, and ascorbic acid. D’Aquino et al. (2017) observed that sodium hypochlorite (200 mg/L) along with a very low dose of imazalil

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(50 mg/L) could enhance storage life of film-wrapped lemon without impairment in quality. 2.24

VALUE-ADDED PRODUCTS AND PROCESSING

Value addition of citrus can be a very good option as the market price of citrus falls enormously during high production period. To overcome the market glut situation and fetch a higher return, processing can be a very virtuous option. Major value-added products prepared from citrus are sour-sweet in taste. Products, such as juice, frozen concentrate, nonfrozen concentrate (NFC), squashes, syrups, jam, jelly and marmalade. Besides dehydrated citrus products have also enormous demands. Citrus peel can be also used as food product by removing the bitter component naringin. Citrus peel was subjected to β-cyclodextrin dosage and de-bittering techniques. Maximum elimination rate of naringin was 82.93% when the β-cyclodextrin quantity was 0.6% (m:m), milling time was 30 min, de-bittering temperature was 40°C, and de-bittering time was 60 min (FeiFei et al., 2017). 2.24.1

CITRUS JUICE

Various citrus species can be harnessed for the purpose of juice extraction from hairy placenta. The juice has several medicinal properties and are rich in vitamin C. Pummelo juice, orange juice, Mosambi juice are prepared by pressing of the hairy placenta. They have enormous demand in the market. Pressing of the integuments for juice extraction is a better method as compared with top crushing of the entire albedo. This is because during crushing, the seeds also get crushed leading to bitter juice. The bitterness of the seed is due to limonene present in seeds. 2.24.2

JUICE CONCENTRATE

Juice concentrate as the name suggests is the concentrated form of any juice. It is of two types: nonfrozen juice concentrate (NFJC) and frozen juice concentrate (FJC). NFJC and FJC are prepared from orange juice. Frozen concentrated orange juice (FCOJ) is prepared by heating the juice and evaporation of required amount of water from the orange juice. The end

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point is achieved when 65º Brix is achieved. Then the concentrated juice is stored at freezing temperature (20ºF). In the case of NFC orange juice freezing is not needed. 2.24.3

SEED OIL

Citrus seeds are also having enormous potential biochemical components. Citrus seeds are known to have 30–45% oil dry weight basis. The seed oil taste is however bitter due to limonene and hence is not consumed directly. Citrus seed oil is an abundant source of fatty acids and is harnessed for the manufacture of pharmaceuticals, scenting soaps, cosmetics, and deter­ gents. Fatty acids, such as palmitic acid (22.30%), stearic acid (2–5%), oleic acid (20–25%), linoleic acid (37–45%), and linolenic acid (3–5%) are present in citrus seeds. The seed meal contains abundant protein (32.5%), fat (7.5%), and crude fiber (8%) and hence can be used with animal feed. The important components of seed oil are linoleic acid, sesquiterpenes, phytosterols, monoterpenes, and oxygenated monoterpenes (Ndayishimiye et al., 2017). 2.24.4

PEEL OIL

Citrus peel or the flavedo has numerous oil glands with oil embedded. The oil if extracted properly can be used to produce several value-added products, including citrus flavored confections, beverages, and baked products. Oil extracted from the peel can be used extensively in pharmaceuticals, cosmetics, soaps, detergents, and perfumes. The oil sacs are ruptured mechanically to extract the oil. Generally, the flavedo is pressed to extract the oil. As heating is not done to extract the oil, hence it is known as cold-pressed oil extraction (Attaway and Moore, 1992). 2.24.5

PECTIN

Citrus is rich in pectin and hence pectin can easily be extracted from citrus. Pectin is responsible for the viscosity of the processed product made of citrus. It acts as a stabilizing agent in manufacturing jam, jelly, and marmalade. Pectin is extracted from pummelo rind by using alcoholic extraction method (John et al., 2017; FeiFei et al., 2017).

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CITRUS MOLASSES

Citrus molasses is prepared by treating the composite mixture of peel and pomace with 0.20–0.50% calcium hydroxide (lime). The mixture is then allowed to react and release the remaining juice/liquor from lime-treated peels. The juice/liquor is concentrated to get molasses. The pressed liquor/ jell consists of around 9–15% water-soluble solids (60–70% sugar). The concentrated molasses can be mixed with citrus pulp to sweeten the cattle feed. Chamebon et. al. (2017) observed the fattening of Zel male lambs when citrus pulp silage was fed to them. 2.24.7

FLAVONOIDS

Citrus flavedo is of negligible utilization but is a rich source of flavonoids. These are rich source of antioxidants and have a high-therapeutic value against diseases, including allergy and inflammation. It can reduce athero­ sclerosis and capillary fragility (Attaway and Moore, 1992). Hesperidin and naringin are the major flavonoids commercially produced from citrus waste. Hesperidin solution is somewhat tasteless, but is harnessed as therapeutic agent in pharmaceutical industry. Naringin is an antimalarial component and is used to impart slight bitter taste in food products including beverages. 2.24.8

FLAVOR

A hydrocarbon d-limonene which is extracted from pressing of citrus seeds is utilized as a flavoring compound for manufacturing perfumery compounds and herbal tea. Various process of limonene extraction, such as ammonium sulfate precipitation, water extraction and resin adsorption were tried from pummelo peel and was found that 4.7 mg/g limonene could be extracted by water and further recovered by ammonium sulfate precipitation with a yield of 2.4 mg/g (YuanFan et al., 2017). 2.24.9

CAROTENE

β-Carotene is known to impart yellow to orange color in applied form as well. β-carotene extracted from citrus peel is used as a natural coloring agent in food products (FeiFei et al., 2017).

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2.25 DISEASE, PEST AND PHYSIOLOGICAL DISORDERS OF CITRUS 2.25.1

DISEASES

2.25.1.1 CITRUS CANKER Citrus canker is a disease which is caused by a bacterium Xanthomonas campestris pv. citri. The disease is marked by an appearance of tiny yellow spots on the leaves, twigs, and fruits. Later on, the spots enlarge and coalesce with each other and form bigger yellow hallow. As time progresses, the yellowed portion starts browning. Sour lime is highly susceptible to this disease whereas mandarin and lemons are resistant. Removal of the affected portions is based on eradication principle and can manage the problem. Besides, application of neem water spray @1 L/2 gallons of water, streptocycline or streptomycin @3 g/3 gallons of water and streptomycin sulfate @500 ppm can manage this problem. 2.25.1.2 POWDERY MILDEW This disease is due to fungal pathogen Oidium tingtanium. Whitish powdery spots appear initially on the younger leaves and then on the older ones. Affected leaves become folded and misshaped. The active photosynthetic area is reduced and yield and quality are affected. Fruits if developed are very small in size. The leaves tend to fall in the case of very serious infection. Premature fruit drop and symptoms of dieback may also be visible. Powdery mildew is managed by the application of sulfur-based fungicides, such as Karathane @2 ml/L water, Wettable sulfur (5 g/L water), and sulfex @0.3%. 2.25.1.3 ANTHRACNOSE This is a fungal disease in citrus which is due to Colletotrichum gleospo­ rioides. The fungus mainly affects the leaves, twigs, and fruits. Initially, brown corroded patches appear on the skin, later on these spots enlarge and merge with each other. Then these patches form cater hole-like depression. The margin and tip of the leaves are mostly affected. The twigs and young leaves get folded, shrivel, and fall off. The flowers and fruits also drop off

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prematurely. The disease can be managed by the application of Dithane M 40 @2 mL/L of water. 2.25.1.4 PINK DISEASE This is a fungal disease due to fungi Corticium salmonicolor. The branches start drying up from the top. The affected branch gets covered with fine silvery white mycelium. The bark starts shredding longitudinally. Discolor­ ation, shedding, and drying of leaves take place. Management of pink disease can be done by drastic pruning of affected trees, spraying of Carbandazim @1%, and application of 0.2% foltaf 3 times after 28 days. 2.25.1.5 GUMMOSIS Gummosis is a rot disease which mainly affects the lower portion of the tree trunk. The bark splits and the stem bleeds. The wood is found to be brown-stained and appearance of vertical cracks is visible. This is caused by the fungi Phytophthora palmivora, P. citrophthora, and P. parasitica. Gummosis is managed by the application of Bordeaux mixture. If applied as a paste in the early stage of incidence, the fatal consequences can be reduced. 2.25.1.6 SCAB This is a fungal disease caused by Elsinoe sp. Corky irregular lesions appear on the fruits, leaves, and buds. The affected fruits are hard and devoid of any juice. Scab can be managed by the application of Blitox @0.4%, Bavistin @0.05%, Foltaf @0.25%. 2.25.1.7 GREENING Greening is caused by mycoplasma. Infected plants show yellowing of the leaves and appear chlorotic. Initially, the leaf blades get thickened and twigs are shortened. Later, the leaves shed down and dieback symptoms appear. Fruits in the affected tree are darker green in color and are deformed in shape, biochemically poor, and produce sterile seeds. The disease can

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be managed by controlling the population of Citrus psylla and removal of affected trees. 2.25.1.8 TRISTEZA This is a viral disease also known as Quick decline. The symptoms can be marked by leaf fall, decay of the root, and drying of the terminal portion. The main symptom of tristeza is stem pitting. The barks dry off and ultimately the entire plant dries off. If the branch is broken down, then honeycomb structure is visible. Tolerant rootstocks, such as Citrus jimbiri, Cleopatra mandarin, Rangpur lime, and C. trifoliate can reduce the disease. Managing the aphid population by using systemic insecticides is most important. 2.25.1.9 EXOCORTIS This is another viral infection of citrus in which the rootstock is affected. The bark appears distorted and scaly. Exocortis is better managed if prevented from occurring which is done by using resistant rootstock. 2.25.1.10 XYLOPOROSIS Hole is formed in the stems from which thread-like structure appears. Gum pocket is also observed in the later stage of infection. It can be managed by chopping down the affected tree and by using resistant rootstocks, such as Sweet orange and trifoliate orange. 2.25.2

INSECT PEST

2.25.2.1 CITRUS BUTTERFLY This is a Lepidoptera pest which cuts and chews young developing leaves of citrus. It is known as Papilio demoleus. It also feeds on developing flowers and developing fruit stalk. It can be managed by the application of Malathion @0.01% every fortnight interval.

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2.25.2.2 APHIDS It is scientifically known as Toxoptera citricida. The aphids appear in large number and generally feed on the lower portion of the leaves. They suck the cell sap from tender leaves and twigs. It is a vector for tristeza virus. 2.25.2.3 MITE It is scientifically known as Tetranychus fijiensis. It feeds on both sides of the leaves and developing buds. It produces multiple greyish spots and affects the photosynthesis. 2.25.2.4 MEALY BUG This pest is Psuedococcus sp. which sucks the plant sap causing defoliation and fruit drop. It also secretes honey dew-like sticky substance on the leaves and fruits. This also invites secondary fungal infections. Tying of rubber band on the tree would prevent upward movement of the pest from soil to the tree and save the tree from the mealy bug infestation. 2.25.2.5 CITRUS PSYLLA It is scientifically known as Diaphoria citri. It sucks cell sap from leaves and twigs. The nymph releases honey dew-like substance which further invites fungal infections. This leads to a decrease in the photosynthetic area and leaves fall off. It also carries mycoplasma responsible for greening. 2.25.2.6 CITRUS TRUNK BORER The pest is Anoplophora versteegi and is a serious threat to Khasi mandarin, Sikkim, or Darjeeling mandarin. The pest bores the tree trunk and makes hole, affects the cambium and ultimately the entire plant collapses. This can be treated in the early stage by prophylactic coating of the tree trunk.

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2.25.2.7 NEMATODES Nematode infestation is a very persistent and a major factor responsible for the slow decline of citrus. These nematodes usually injure the root bark, extract essential plant nutrients, and thus disturbing the usual growth of plants. Citrus nematode (Tylenchulus semipenitrans), Pratylenchus coffeae, Rotylenchulus reniformis, Radopholus similis, Meloidogyne javanica commonly affects citrus. Neem cake treatment can reduce the nematode infestation. Application of Carbofuran @1000 ppm, Aldicarb 6 kg/ha or Monocrotophos @1 g/ha can control nematode infestation. 2.25.3

PHYSIOLOGICAL DISORDERS

2.25.3.1 CITRUS DECLINE It is a complex disorder which is due to several prevailing factors. The symptom is marked by a significant but gradual loss in reproductive vigor of the trees, death of several twigs and ultimately leads to reduction in total yield. The orchard looks dull and leaves are chlorotic. The ultimate fate of such orchard is zero production. Nutrient imbalance in plants and soil is one such factor. Both excessive and deficient nutrient can be hazardous. Excess zinc (Zn) results in leaf burn and iron chlorosis. Excess phosphorus pucker and distort rind in citrus fruits. Excess copper (Cu) makes plant underdeveloped, produce dark nonfibrous roots, and iron chlorosis. Whereas deficiency of Zinc (Zn) leads little rosette leaves, molybdenum deficiency results in yellow spots, copper deficiency leads to dieback symptoms. Pres­ ence of excess salt and pH more than 6.5 can be deadly for citrus. This can be avoided by selecting proper site by soil testing and slope judgment. The soil should be free from phytopathogenic microorganisms, soil must contain sufficient organic matter, planting of virus-free healthy planting material, provide optimum INM, proper management of pest, and follow good horti­ cultural practices to ensure that decline is not persistent (Sharma, 2005). 2.25.3.2 FRUIT CRACKING Cracking of the fruit can be due to deficiency of the nutrient and also due to disturbed water balance caused by fluctuating irrigation. The immature fruit seen with a thin peel which cannot expand quickly is more susceptible.

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After long dry spell if it suddenly rains, the fruits tend to crack. It is high in baramasi lemon. Application of Ca can somewhat solve this problem. It is also advocated to apply frequent light irrigation during summer months. 2.25.3.3 SUN BURN This is due to hot, sultry heating of fruits during the summer months of April to June. Damage symptoms are more pronounced in fruits than any other part of the plant. Sun burn fruits are darker in color which gradually turns brown. With high exposure, the pulp also gets affected. This can somewhat be controlled by planting shade trees toward south and west by mulching and providing supplementary irrigation during sultry summer. 2.25.3.4 HAIL DAMAGE This is the effect of damage due to hail storm. The branches, leaves, and fruits can get injured. Wounds can also be seen on branches, leaves and fruits. Excessive flower and fruit drop may also occur. The symptoms are similar to those injury done on fruits by birds. 2.25.3.5 WIND SCAR Abrasion and scars are visible when there is a strong wind that blows off plants significantly to cause one branch to injure the other and damage the foliage and fruits. The damaged portion get more and more exposed to pest and other infestation. 2.25.3.6 STEM-END RIND BREAKDOWN This is marked by collapse and browning of the flavedo near the stem end of the fruit. The symptom can be marked as development of undeveloped mass of cell devoid of stomata or any pigmentation. Over the skin, heavy layer of cuticle is also formed. This is due to excessive dehydration of the peel surrounding the stem end. Thin peel fruits are more susceptible to this disorder (Albrigo, 1972).

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2.25.3.7 GRANULATION This is also known as crystallization and dry end. The symptom can be marked as the drying of the fruits starting from the stem end which moves toward style end. The fruit becomes hard and dry due to desiccation of the juice glands. The fruits become somewhat enlarged in size and have dull smell and taste. The fruit have high gelatinous matter and less juice. High Ca–Mn and low P–B is responsible for this malady. The malady can be abridged by 50% by 2–3 sprays of NAA (300 ppm) in the months of August, September, and October. Spraying of GA@15 ppm followed by NAA@300 ppm in month of October and November also diminish this problem. 2.25.3.8 DELAYED GRAFT INCOMPATIBILITY This is more visible in later stage when there is a graft union initially but the graft union failed to show compatibility in later years. The delayed incom­ patibility is visible anatomically as the fruiting and overall plant loses vigor. The plant does not produce significant fruiting, and necrotic spots are also visible. Some cases of delayed incompatibility were visible when mosambi or Blood Red variety was grafted on Citrus jimbiri (Rough lemon). 2.25.3.9 OLEOCELLOSIS Oleocellosis is also a postharvest disorder that is marked by spotting of damaged portion along with oil split on the outer flavedo. The flavedo is initially yellow and starts browning with time. This is the formation of necrotic spot due to rapture of the oil gland on the skin. The oil gland can get ruptured due to fruit harvest drop from the tree or improper handling during storage, transport, and marketing. It can also take place if citrus is pressed by fingers (Knight et al., 2002). 2.25.3.10 COLD INJURY OR CHILLING INJURY Citrus is very much susceptible to cold temperature preservation (Schirra and Mulus, 1995). Lime, lemon, mandarin, pummelo, and grapefruit are most susceptible to chilling injury below 3.5°C. The symptom may be marked as formation of brown pith-like depression in the flavedo. This may also

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affect the albedo in longer run. At last, the depressed lesions are formed which eventually breakdown with increasing storage duration (SanchezBallesta et al., 2003). The brown color is due to enzymatic oxidation of di-hyroxyphenylalanine. To ensure minimum chilling injury, citrus can be stored at temperature more than 5°C. Lemon and lime can be stored at 6–7°C. Chilling injury susceptibility is less if storage is done at high relative humidity (Pantastico et al., 1971). 2.25.3.11 RIND STAINING This postharvest disorder is also known as non-chilling peel pitting. Tangerines and oranges are most susceptible to this disorder. The symptom of this disorder includes appearance of small brown necrotic spots over the oil gland. Fruits stored in elevated CO2 and low O2 are highly susceptible. Waxed fruit which gets lesser O2 is also susceptible to this disorder (Patracek et al., 1998). KEYWORDS • • • • • • • •

citriculture citrus citrus growing classification breeding rootstock diseases physiological disroders

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CHAPTER 3

DURIAN Tran Van Hau1*, Doan Huu Tien2, Nguyen Minh Thuy1, Huynh Ky1, Tran Thi Oanh Yen2, Mai Van Tri3, Nguyen Van Hoa2, and Tran Sy Hieu1 Crop Science Department, College of Agriculture, Can Tho University, Vietnam 1

Southern Horticultural Research Institute, Long Dinh, Chau Thanh, Tien Giang, Vietnam

2

South East Horticultural Research Center, Ba Ria, Vung Tau, Vietnam

3

Corresponding author. E-mail: [email protected]

*

ABSTRACT Durian is a unique tropical fruit which is grown in various nations of South­ east Asia, primarily in Thailand, Indonesia, Malaysia, Vietnam, and the Philippines. Its fruit has a very strong aroma which is unbearable for some people, especially those living in the Europe or the USA. Therefore, the fruit is consumed primarily in Asia, particularly China, Hongkong, Taiwan…. “Monthong” of Thailand is the most favorite durian cultivar, which is now growing in various countries, for example, Malaysia, Vietnam, Philippines. Flowers of durian arise on lateral and main branches and occasionally on trunk. Anthesis occurs in the afternoon, from 4:00 to 8:30 PM. The peaks of pollen reception of stigma and pollen release of anthers do not overlap, thus hampering fruit setting. In addition, the latter was reported to be influ­ enced by complete or partial self-incompatibility. Therefore, supplemental/ hand pollination is crucial for high fruit set rate as well as high yield. Since Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing. Debashis Mandal, PhD, Ursula Wermund, PhD, Lop Phavaphutanon, PhD & Regina Cronje, MSc (Eds.) © 2023 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

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both flowers and fruits appear on branches, vegetative flushing during the fruit-bearing stage will bring about immature fruit drop and physiological disorders which reduce fruit yield and quality. Fruit physiological disorders appear in different forms, namely, hard flesh with/without decoloring, watery aril, wet core, and tip burn. The period from anthesis or fruit set until harvest varies depending on the variety and climate, on average 90–135 days. In Malaysia, fruits are harvested after being completely ripen and dropping down from the tree. Instead, in Thailand and Vietnam, mature fruits are cut and subjected to ethephon treatment to induce uniform ripening. Year-round production of durian was made possible by manually creating drought condi­ tion (applying plastic mulching and complete drainage of irrigation ditch) and foliar spraying with Paclobutrazol at 1000–1500 ppm. 3.1 GENERAL INTRODUCTION Durian is a high economic value fruit tree grown primarily in the Southeast Asian countries. The world leading producer and exporter of durian is Thai­ land. In 2016, this country exported 431,725 t, accounting for 83.4% of its total production. China is the primary market with increasing demand in the recent years which is an important driving force for durian growers to quickly increase durian area and production. To obtain high yield and good quality, it requires strict management in all processes of durian cultivation, that is, variety selection, planting, caring, and pest control. There are plenty of durian varieties/clones in the world. However, the three cultivars of Thailand, “Monthong,” “Chanee,” and “Kanyao” are the most popular. In addition, breeding programs in many countries have resulted in some new cultivars released to the farmers. It is necessary to accommodate more than one durian variety in an orchard to increase fruit set. Also, suitable varieties, good spacing, proper training and pruning are important factors leading to early harvesting and high yield. Physiological disorders are the most important factor influencing fruit quality. These require appropriate management techniques adjusting for different varieties, climate, soil nutrition, and humidity status. In tropical region, durian flowering requires a relative long period of dry climate or drought to be able to commence flowering. In Malaysia, where there is short or no dry season, durian trees may not flower for 1–2 years. Therefore, techniques to induce flowering is very important for both on- and off-season flowering of durian. In particular, durian prices in off-season are usually

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much higher than that in on-season. Hence, off-season flowering techniques have attracted much attention from researchers and growers. Harvesting technique, postharvest treatments and processing are the key factors to increase the value for durian. In Malaysia, fruits are harvested after being completely ripened for domestic consumption. Instead, in Thailand and Vietnam, mature fruits are harvested and treated with ethephon to induce uniform ripening, which is suitable for fresh fruit exportation. Treatment to induce uniform ripening is also a measure to reduce the effect of physi­ ological disorders reported on “Monthong” cultivar. Processing of fruit flesh has also been studied to diversify the product range and increase value for durian. 3.2 AREA AND PRODUCTION Durian is commercially produced in many countries in the world. According to data collected in 2016, Thailand (100,000 ha; 656,777 t1) was the leading producer of durian, followed by Malaysia (66,038 ha; 302,000 t2), Indonesia (50,000 ha; 735,420 t3), Vietnam (28,000 ha, 288,149 t4), and the Philippines (16.600 ha, 71,444 t5) (Janick and Paull, 2008; Ketsa, 2018). In addition, the fruit crop is also grown at smaller levels in the other countries of the ASEAN, Australia (Darwin of Northern Territory and Tully to Cape Tribula­ tion of Queensland), Sri Lanka, Papua New Guinea, and India (Yaacob and Subhadrabandhu, 1995; Ketsa, 2018). In Thailand, durian is primarily planted in provinces in the East (Chan­ thaburi, Rayong, Chumphon and Trat) and West (Nakhon Si Thamarat) (Somsri, 2017), of which, Chanthaburi is referred to as the “capital” of Thai durian. Due to geographical differences, these growing regions have different crop seasons (between April and July for the eastern provinces, July and September in the South, and June and July in the North) (Lim and Luders, 2009). While being the largest durian exporter being able to supply roughly 50–60% of the total world’s demand, the greatest portion of Thai durian (83.4% of overall production) is domestically consumed (Ketsa, 2018). In Malaysia, because of monsoons, namely, northeast (November–March) and southwest (June–August), as well as the shift from wet to dry condition, Office of Agricultural Economic, Ministry of Agricultura and Cooperatives, Thailand, 2017. New Strait Times, Dec. 3rd, 2017.

3 https://www.statista.com/statistics/706504/production-of-durian-i.

4 Department of Agriculture, Vietnam.

5 Department of Agriculture, Bureau of Plant Industry, Philippines.

1 2

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durian areas are divided into three regions (1) North region, (2) the region of West, Central and South, and (3) coastal area in the East including Sarawak and Sabah of Borneo island (Lim and Luders, 2009). The latter has two fruiting seasons, namely, June–August in both places and a small season in Sabah occurring in November–December. Most of the durian produced in Malaysia is for domestic consumption. Malaysian durian is exported to its nearby countries Singapore and Brunei (Ketsa, 2018), but in April–May durian products from Thai is imported to Malaysia (Subhadrabandhu and Ketsa, 2001) to serve its out of season demands. In Indonesia, durian is grown in islands scattering over both sides of the Equator. For the northern part, durian production is distributed primarily in Sumatra Island with a crop season similar to the other countries of Southeast Asia. The most part of Indonesian durian production is located in the South with harvesting season occurring from October to February of the next year. Indonesian growers usually grow durian in small scale, intercropping with the other fruit trees or rubber in agroforestry systems (Langford, 2014). Durian in Vietnam is grown primarily in the country’s southern part, that is, the Mekong delta (MD), Southeast, and Central highlands. In the MD, Tien Giant province is the largest durian growing area, accounted for 40% of the total durian area of the whole country. In the Southeast region, durian is grown mostly in Dong Nai province, while the durian growing areas of Central highlands are in Lam Dong and Daklak province. The three mentioned regions are different in terms of elevation, thus the differences in water availability and application of flowering induction techniques. The MD is a flat and low elevation plain, hence water for irrigation is available year-round, making it possible for year-round production. Contrarily, since the elevation of the Southeast and Central highlands (50–500 m above the sea level) is higher than that of the Mekong delta, these locations suffer from lacking water in the dry seasons. Consequently, durian is left to flower naturally depending on the climate and harvested in July–September. 3.3 MARKETING AND TRADE Durian production from Thailand, Indonesia, Malaysia, and Vietnam supplies to both domestic markets and export. While being a durian producer, some countries in Southeast Asia also import durian from the others in the same region. For example, in 2016, durian of Thailand was exported to Vietnam (84,850 t), Malaysia (2573 t), and Indonesia (1959 t) (Saowanit, 2017), who

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are also large durian producers and exporters. While the world market of durian is dominated by Thailand, some other countries in Southeast Asia (primarily Malaysia, Vietnam and Indonesia) are also expanding durian exportation with various kinds of products, such as fresh, dried, and frozen durian. Thailand is the largest exporter of fresh and frozen durian. The importers of Thai durian include Malaysia, Indonesia, Vietnam, Japan, the USA, China, Taiwan, and Hong Kong with China being the major market, importing 158,080 t, accounting for 39.3% of the total export volume of Thailand (Saowanit, 2017). During the time from 2008–2016, the total amount Thai durian exportation, as well as the amount of fresh durian shipped to China showed an increasing trend by year. In 2016, according to Hnin (2017), the total export volume of Thailand durian was about 402,640 t. Besides fresh fruit, Thailand also exports frozen durian (8287 and 12,496 t in 2014 and 2016, respectively) and dried products (Saowanit, 2017). Malaysia exported 20,000 t of durian in 2015. China is also the biggest market of Malaysian durian with about 14,000 t exported in 2017. Frozen fruits or processed products of Malaysia are sold directly to China, but the fresh fruits have to be traded through other countries like Hong Kong or Thailand before being shipped to China. Of recent years, Vietnam has been exporting durian to various countries worldwide, but China is again the largest market. The statistics showed that in 2017 alone about 66% of the total durian production of Vietnam was for export, resulting in a value of US$ 319.69 million.6 The primary importers of durian from Asia are China, Singapore, Hong Kong, and Taiwan. In China, durian ranked fourth in China’s fruit imports with a compound annual growth rate of 12% in terms of imported weight and an increase of 31% in value recorded from 2010 to 2015. In 2015, China imported fresh durian from Thailand and Malaysia, a total of 299,000 t which is worth US$ 568 million, not including durian paste and other durian products. Currently, thanks to the increase of durian demand and consump­ tion in China, the total production and export of durian in Thailand as well in other Southeast Asian countries have grown fast. Hong Kong is the second largest durian importer consuming about 36% of the export from Thailand with 146,320 t in 2016.

Department of Vietnam Customs, Bulletin of Trade Information. Feb 12–19, 2018.

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3.4 COMPOSITION AND USES Durian, considered as the “king of fruits” in Southeast Asia, is peculiar for its large-size fruits, strong smell, and its rind is covered by thorn. The largest fruit size can be 30 cm long and 15 cm in diameter, and the fruit weight can vary from 1 to 4 kg (Heaton, 2006). 3.4.1 USES OF DURIAN In Asian countries, durian is primarily sold as whole fruits, and freshly eaten. During ripening, durian fruits have a strong aroma, and therefore they can be used to flavor a wide variety of candy, biscuits, ice cream, and mooncakes. The dish, namely, “Pulut durian” or “Ketan durian” is glutinous rice steamed with coconut milk and served with ripened durian (Heaton, 2006). Durian is often served fresh with sticky rice in Thailand, and durian paste is commonly sold in the markets (Morton, 1987). 3.4.2 HEALTH BENEFITS OF DURIAN FRUIT Apart from nutrients, durian is rich in bioactive compounds (Ho and Bhat, 2015) and it can be used as an active ingredient for the development of functional foods. Durian fruit is high in fiber, which helps in reducing LDL cholesterol to protect the cardiovascular system. It also contains important minerals, such as P, K, Ca, Mg, Na, Fe, Mn, Cu, and Zn, and it possesses high content of carbohydrate, protein, and fat (Health Benefits of Durian, 2015). Fatty acid compositions bring about durian health benefits (Leontowicz et al., 2011). The content of n-3 fatty acids and the bioactive compounds (polyphenols, quercetin, flavonoids, flavanols, tannins, anthocyanins, ascorbic acid, and carotenoids) found in durian are higher than in other fruits. “Monthong” cultivar is a typical example (Dembitsky et al., 2011). Ripe durian is reported to contain relatively high amount of polyphenols and flavonoids as compared with mature and overripe durians (Leontowicz et al., 2008). This fruit is found as a good source of vitamin C which acts as an antioxidant (about 33% of RDA) and is a rich source of B-complex groups of vitamins (niacin, riboflavin, pantothenic acid, pyridoxine, and thiamin) which are essential for the human body (according to USDA National Nutrient Database).

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3.5 ORIGIN AND DISTRIBUTION Historically, the big family—Bombacaceae had been established by combining the three subtribes, namely, Adansonieae, Matisieae, and Durio­ neae (Schumann, 1895). Therefore, the former genus Durio belonging to Durioneae had been classified in Bombacaceae family based on the morphology of its leaves. Although well-known in Southeast Asia, the first description of Durian was noted by Nicolo Conti, a westerner, who traveled in Southeast Asia at the beginning of the 15th century (Bracciolini, 1857). In that description, durian was reported to have originated from Borneo and Sumatra, and it grew wildly in the Malaysian Peninsula. Therefore, the word “durian” was adopted from a Malaysian local word—“duri” (which means “spine” in English), and the word “zibethinus” is a reference to the smell of the Indian civet cat (Viverra zibetha). Similar to the earliest report, Hawson (1983) and Watson (1984) had proposed that “zibethinus” might be associ­ ated with the fact that the specific fruit's scent is similar to that of the civet cat. On the other hand, Don (1831) proposed that the durian fruit was used as bait to entrap the civet cat. While being traded across Southeast Asia for more than 400 years ago, durian was grown in the local villages probably from the late 18th century and has been commercialized since the middle of the 20th century. The plant has since been widely cultivated in various countries in Southeast Asia, namely, Thailand, Laos, Cambodia, Vietnam, Malaysia, Brunei, Indonesia, and the Philippines (Morton, 1987), and such places as southeastern Papua New Guinea, Honduras, Zanzibar (in Africa), Northern Territory, and Queensland of Australia (Brown, 1997). 3.6 BOTANY AND TAXONOMY Durian (Durio zibethinus) belongs to the tropical family Bombacaceae, known for its showy flowers and pods with seeds covered with cotton-like fibers (Macmillan, 1949; Janick and Paull, 2008). According to Malo and Martin (1979), the fruit of the “Durio” genus differs in having large seeds with fleshy arils. Among the 27 species of the genus (Soegeng-Reksodihardjo, 1962) durian, D. zibethinus is the most wildly cultivated species, primarily distributed in the countries of Southeast Asia. In the past, durian was mostly propagated sexually, thus the great diversity in fruit size, spines shape, flesh color, and odor emitted.

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Durian trunk has an average height from 10 to 15 m, with a maximum of 50 m. The height of grafted trees is normally 8–12 m (Nakasone and Paull, 1998). Durian has a straight upright trunk, with a fairly rough brownish shell. Durian leaves usually grow alternately. Leaf shape varies from elliptic to oblong, 10–18 cm long and 5–7 cm wide. Upper leaf surface is normally dark green in color, flat and glossy; and the lower surface is light brown in color. The flowers of durian usually appear in clusters and directly emerge from scaffold branches or trunk. Each cluster has 1–45 flowers, which are pendulous and white in color. During anthesis, flowers emit very strong aroma. Size and weight of durian fruit vary depending on the varieties, on average 15–30 cm in length and 10–20 cm in diameter, 2–4 kg in weight. Fruit shape can be round, elliptic, or oblong with sharp spines and different skin colors, that is, greenish grey, greenish yellow, yellow or reddish yellow. When durian fruits start to mature, the color of the pulp turns from white to cream, yellow, orange or red depending on their varieties. Seeds of durian can be big or small, on average 2–6 cm long (Nakasone and Paull, 1998), the color of seed coat includes yellow, brown, or red-brown. 3.7 VARIETIES AND CULTIVARS The most common durian cultivars commercially grown in Southeast Asia originated from D. zibethinus Murray that is native to the Malaysian Peninsula (Voon et al., 2007). According to Nanthachai (1994), commercial cultivars arise from various sources, including chance seedlings, selection by farmers as well as breeding programs managed by governmental institutions. The selection activities are found most active in Thailand and Malaysia, where quite a few new varieties have been developed and released. In Thailand, there were more than 200 durian varieties. However, only 60–80 varieties have been commercially grown (Lim and Luders, 2009). These varieties were grouped based on maturity (Bamroongragsa and Yaacob, 1990) or fruit and leaf parameters (Hiranpradit et al., 1992). For maturity, there are three groups of durian varieties, namely, early maturity (103–105 days), medium maturity (127–130 days) and late maturity (140– 150 days). The six groups of Thai durians classified in accordance with the characteristics of fruit and leaf include (1) “Kob” (38 varieties); (2) “Lueng” (7 varieties); (3) “Kan Yao” (7 varieties): (4) “Kumpun” or “Gumpun” group (11 varieties); (5) “Tong-yoi” (12 varieties); (6) Miscellaneous (47 varieties). “Monthong” and “Chanee” are the two most favorite cultivars, accounting

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for 41% and 33%, respectively of the total durian area of Thailand (Alim et al., 1994). Moreover, these two cultivars are now growing widely in the other ASEAN countries and Australia (Lim and Luders, 2009). In Malaysia, even though >200 durian clones have been registered by the Malaysian Agriculture Department, only 20% of the area was planted with clones while the rest was the area of indigenous cultivars (Voon et al., 2007). Among the eight durian clones (namely, “D2,” “D10,” “D24,” “D99,” “D145,” “MDUR 78,” “MDUR 79,” and “MDUR 88”), the commonly culti­ vated clone “D24” is extensively cultivated, occupying 70–80% of the total clones planting. Furthermore, 134 other clones have been recommended by the Malaysian Agricultural Research and Development Institute (MARDI) (Lim and Luders, 2009). For the other ASEAN countries, many many durian varieties have been reported. The three local varieties selected and grown in Singapore include “H.C. Tan No.2,” “H.C. Lim,” and “Lim Keng Meng.” In Indonesia, 15 superior national varieties have been released, namely, “Bokor,” “Kani,” “Otong,” “Perwira,” “Petruk,” “Si Dodol,” “Si Hijau,” “Si Japang,” “Si Mas,” “Sitokong,” “Siwirig,” “Sukun,” and “Sunan,” Furthermore, many more varieties have been found in the other islands of Indonesia, particularly Sumatra. In the Philippines, the recommended durian cultivars are “DES 806,” “DES 916,” “Umali” and “CA 3266.” In the MD of Vietnam, there are plenty of local cultivars arising from seed propagation, for example, “Ri 6,” “Sua Hat Lep” (“SHL”), “Kho Qua Xanh” (“KQX”), “Chuong Bo.” 3.8 BREEDING AND CROP IMPROVEMENT Conventional breeding has been used to develop new durian cultivar in many ASEAN countries. In Thailand, durian breeding program has been conducted for over five decades; hand cross-pollination was used to generate hybrids since 1986. Until 1990, 55 crosses were made, resulting in 7634 F1 seedlings (Somsri and Khaegkad, 2002). Subsequently, in 1998–1999, 51 crosses were made, producing 4278 F1 seedlings. Moreover, interspecific hybridization was implemented in the period from 1988 to 1992 with 45 crosses, and in 2000 with 21 crosses. These works resulted in 111 F1 seedlings and F2 popu­ lations. In 2012, other 18 crosses were done, producing 1373 F1 seedlings. Later, 29 promising lines were selected based on various evaluation criteria: good eating quality (good flavor, aroma and texture), medium fruit size, and thick flesh, high percentage of flesh and aborted seed, maturity index, high

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fruit setting rate, and high yield (Somsri, 2015). Until now, six F1 hybrids were released to farmers (Somsri, 2014), namely, “Chanthaburi 1,” “Chan­ thaburi 2” and “Chanthaburi 3” (2006); “Chanthaburi 4,” “Chanthaburi 5” and “Chanthaburi 6” (2013). In Malaysia, durian breeding programs were started in the early 1980s. After 20 years of screening, MARDI developed and released some cultivars from hybridization, including “MDUR 78,” “MDUR 79,” and “MDUR 88.” In Vietnam, since 2007, a durian hybridiza­ tion program has been undertaken by the Southern Horticultural Research Institute (SOFRI). The program resulted in three promising hybrids coded as “RM20,” “RM21,” and “RM22.” These possess good characteristics, such as high fruit quality, yellow flesh, high aborted seed rate (70.0–85.7%). Molecular approach and marker-assisted selection have also been used in evaluation, selection, and characterization of new crosses. DNA amplifica­ tion fingerprinting was used to identify the genetic relationships among nine species of the genus Durio, 56 cultivars, 120 F1 hybrids from 24 crosses and 29 promising lines (Somsri et al., 2005a, 2005b). RAPD and ISSR primers were also used to evaluate the genetic diversity on durian (Vanijajiva, 2011; Yen et al., 2014, 2016). SSR was used to analyze the genetic diversity and identification of various accessions of durian clones in Nonthaburi of Thai­ land (Seubsuk et al., 2017). In Malaysia, Siew et al. (2018) reported high levels of genetic diversity (HE = 0.35) found in a study using SSR marker. The results of that study laid a foundation for the management of genetic resources and the future development of strategies for germplasm sampling as well as genetic improvement of durian. 3.9

SOIL AND CLIMATE

Either sloppy or flat land can be used to grow durian. However, these should not be flooded and steeper than 10°. To avoid flooding at flat areas such as deltas, durian should be planted on raised bed. Hot (24–30°C, not lower than 22°C), moist (75–80% RH), and sunny tropical climate, within 16° north and south of the equator are favorable conditions for durian trees. In addition, cool climate at an elevation up to 800 m above mean sea level is also suitable. While durian trees require moist condition to thrive, high humidity during the rainy season will stimulate disease development. In contrast, low air humidity will result in leaf blight. Therefore, regulating humidity in durian orchards to prevent the mentioned issues is necessary. Evenly distributed precipitation (1500–3000 mm) and light wind are also

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favorable condition for durian trees to grow. At flower initiation stage, heavy rain events will affect flowering which requires a dry spell of 1–2 months (Salakpetch, 2005). In addition, during flowering stage, heavy rain falls can also affect pollination and cause flower abscission. Dry period prolonging more than 3 months is harmful for durian trees. According to Hariyono (2017, 2018), durian can be divided into two types based on the environmental requirements. In the first type, called “endemic,” quality and quantity of durian fruits significantly interact with the environment. Accordingly, environmental changes will influence the fruit quality and quantity of durian trees known as local varieties. In contrast, the second type, namely, “pandemic,” can adapt to a wide range of environment factors, soil types, and altitudes. Therefore, durian vari­ eties of the second type are still able to sustain fruit quality and quantity in diverse environmental conditions. Information about the relationship between climatic factors and the phenology of different durian varieties is used as a reference to establish new cultivation practices, aiming to optimize the growth of durian. 3.10

PROPAGATION AND ROOTSTOCK

Durian can be propagated both sexually and asexually. However, seed propagation is not recommended because of unstable fruit quality. In addition, the tree takes long time to bear fruits and has the tendency to grow into large and high canopy making it hard for the caring process. In contrast, asexual propagation is the most common method applied in durian production. In the Philippines, shield budding (or T budding) is a popular method in the propagation of durian. Coronel et al. (1986) stated that air-layering was also found to be successful in some countries, but it was not recommended for large-scale production. That is because trees grow slowly, and the rooted branches are not able to survive after being cut from the tree. In Vietnam, cleft grafting method is used commonly for commercial propagation since growers can produce seedlings in a short time. The success rate of that method is relatively high, 70–80%, and the grafted trees take 4 years to bear fruits. For highlands, the root system of grafted and budded trees can grow deep down to the subsoil layer to absorb nutrients and water, hence better growth. In lowland areas with high ground water level, for example, the MD of Vietnam, air-layering trees may be more suitable because of their shallow root system. However,

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air-layered trees can fall due to strong wind, hence windbreak is needed (Phong, 2010). Inarching of seedlings to mature tree is considered as high-tech and applied in many countries of Southeast Asia and Australia. In Vietnam, Chau et al. (2004) reported that seedlings in arched with two rootstocks grow faster than those inarched with only one. Similarly, in Indonesia, Yuniastuti et al. (2017) also found that seedlings inarched with multiple rootstocks grow better than those inarched with only one. In Thailand and Australia, inarching of 2–3 rootstocks was used to improve the intake of nutrient and water as well as to improve better tolerance against strong wind since the plants have better root system (Boobongkarn, 1960; Lim and Luders, 2009). Furthermore, Zabedah et al. (1992) found that trees inarched with multiple rootstocks showed better fruit set than those with single rootstock. Most importantly, inarching with rootstock that can tolerate well to the root rot disease has been studied as a solution to control the disease. In Vietnam, Uyen et al. (2012) found that “Chanee,” “Kanyao” and “La Queo Vang” (also known as “La Queo Ba Thum”) showed good tolerance against root rot caused by Pythium vexans. In addition, In Thailand, Sangchote (2002) stated that the most resistant cultivar against Phytophthora palmyra was “Chanee.” In contrast, “Monthong,” “Kadoom,” and “Kanyao” were relatively suscep­ tible to the fungus. 3.11 LAYOUT AND PLANTING 3.11.1

LAYOUT

Various layouts can be used for planting durian, that is, square, rectangular, and quincunx (Chetan, 2018). Square layout is the easiest and most popular form for durian planting, in which distances between rows and between plants are equal. Except for the inequality of distances between rows and between plants, rectangular layout is similar to the square system. More plants can be accommodated in rows in the rectangular system than in the square layout. Quincunx layout (filler or diagonal system) is suitable for intercropping purpose in the way that the empty spaces in the center of each square is used up by planting another kind of tree (Phong, 2010). Offset square or offset rectangular layout are modifications of the square or rectangular systems with an exception that the trees in adjacent rows are offset. The triangle layout was also recommended by Janick and Paull (2008).

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PLANTING

The suggested planting distance for asexually propagated durian trees is 10–12 m in the Philippines and 6–16 m in Malaysia. Generally, some other authors suggested 10 × 10 m (100 trees/ha) (Paull and Duarte, 2011) or 8–16 m planting distance (40–156 trees/ha) (Janick and Paull, 2008). Planting should be implemented at the beginning of or during the rainy season. The young seedlings, after being taken out from containers, are carefully set in the pre-prepared holes of 0.4–0.6 m wide and depth and aligned in all direc­ tions before filling the holes. The soil surrounding the base of seedlings is pressed down firmly and is watered after planting (Coronel et al., 1986). In the lowland areas (e.g., the MD of Vietnam), durian should be grown on raised beds to prevent the root system from being flooded. The width of bed is normally 5–10 m with ditches located between the two beds. For smaller ones (5 m wide), the trees are planted as one row in the middle of the bed. Two rows can be grown on large raised bed of 10 m wide. 3.12

IRRIGATION

Since durian is native to the tropical rain forests, it needs warm and moist environment to develop. In Southeast Asia, adequate irrigation is important for durian at regions where dry season is longer than 3 months. Furthermore, a good fertigation system is a requirement where farmers would like to apply intensive management methods and to manage diseases and disorders (Drenth and Guest, 2004). Actual water demands of durian vary depending on various factors, for example, location, weather, tree age, canopy size, and stage of development. Therefore, it takes a lot of time and effort to accurately determine an irriga­ tion schedule for durian. Until now, growers empirically decide the time, amount, and frequency of watering by using tree-based method or soil and weather-based method or a combination of both (Jaafar, 1998). To support the practice, FAO published a document aiming to provide instructions to determine crop’s water requirements and to plan, design, and operate irriga­ tion projects (Doorenbos and Pruitt, 1977). Durian is very sensitive to dry environments and cannot tolerate prolonged droughts because of its shallow root system. Therefore, to achieve high yield and quality, irrigation is very important particularly during flowering and fruit development stage. Within 2 months after planting, if there is no rain, young trees should be shaded and watered daily with 5–15 L/tree. During

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the juvenile stage and afterward, the water amount should be increased in accordance with the growth of canopy size. At mature stage, durian trees in Thailand were irrigated with 200 L of water every 2–3 days (Jerapat and Siriphanich, 2008). In Malaysia, 8–10 L/plant per application every 4–7 days is suggested during the first year of field establishment (Abdul-Jamil and Ghani, 1991). Zainal et al. (1992) recommended daily watering at 6–8 L/ plant to reduce flower abortion. Jaafar (1998) reported that the estimated maximum water need of 360 L/day can be required by a mature durian tree with a normal spacing of 10 × 10 m. In Vietnam, farmers apply surface and sprinkler irrigation using under-canopy sprinklers or microsprinklers as the two common irrigation methods for durian orchards. Drip irrigation is also applied in some orchards (SEHORT, 2016). In the uplands of Highlands and the Southeast region of Vietnam, Tri et al. (2016) reported that the irrigation intervals of 3–10 days were applied commonly during the dry season with a pause of 2–4 weeks prior to flowering. During the time before harvest (2–3 weeks), the plant’s need for water decreases. Hence, the water amount supplied in each irriga­ tion is progressively reduced or cut off depending on weather conditions. In the Highlands region (400–700 m above sea level), surface irrigation was applied widely with the average amount of water is 1600–2000 m3/ha for 5–10 days intervals during the dry season. In the Southeast region, for surface irrigation, average amount of water used for each application is 800–1200 L/tree (or 80–120 m3/ha) applied at 5–7 days intervals. For sprinkler irriga­ tion, the water amounts used in each round were 25–40 m3 per ha at 2–4 days intervals. Water resource used for irrigation in the MD of Vietnam is taken primarily from ditches located between rows and between orchards. On average, the water amount used for surface irrigation per application was 200–400 L for a mature tree applied at the 2–4 days intervals. When sprinkler irrigation was used, that water amount was reduced 40–60%. Mulching is a good method to conserve irrigation water, since it helps to maintain soil moisture within the root zone, particularly during the dry season (Vinh, 2017). Mulching using dried grasses, rice straw, coffee husks, burned rice husks, or other materials should be kept from direct contact with the trunk, and the mulching material should be extended as the plant grows. A good cover of mulch will help to control weeds under the tree canopy, as well as to reduce water evaporation. Trees that are mulched can be irrigated less frequently than those that are not mulched. During the wet season, it may be better to clear the mulch to avoid excessive moisture, which encourages Phytophthora canker development (Drenth and Guest, 2004). In addition, to

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reduce the incidence of Phytophthora diseases, it is important to incorporate a good drainage system within the orchard to get rid of excessive water during the rainy season or overirrigation (Drenth and Guest, 2004). 3.13

NUTRIENT MANAGEMENT

Nutrient management for durian is implemented based on climate, and growth stages of trees. In the rainfed areas with two distinct seasons, where irriga­ tion is relatively restricted during the dry season, 2–3 fertilizer applications during the rainy season are usually recommended. In contrast, for regions where water is available in the dry season, fertilizer amount and number of applications are determined based on the growth and development of both trees and fruits. Nakasone and Paull (1998) suggested applying compound fertilizer (14–4–3.5) two times per year for trees younger than 5 years old. For fruit-bearing trees, 12–4–7 compound fertilizer was recommended at the rate of 0.1–4.0 kg/tree/year with the highest rate applied for 12-year-old trees. The fertilizer composition should also be adjusted for different growth stages. To enforce vegetative growth of 10-year-old durian trees, Nakorn and Chalumpak (2015) suggested a fertilizer composition of 2 kg of 15–15–15 NPK + 15 kg chicken manure, which resulted in the highest flushing rate and the earliest leaf maturation. At fruit-bearing stage (5–7 weeks after fruit set), the composition of N–P2O5–K2O 12–12–17 or 8–24–24 or 13–13–21 can be used. From the 9th–10th week after fruit set, 0N–0P2O5–50 K2O is recom­ mended (Salakpetch, 2005). In Vietnam, for fruit-bearing trees (>6 years old), Tan and Chau (2000) suggested a fertilizer composition of 800 g N + 400 g P2O5 + 400 g K2O + 100 g MgO + 40 kg compost per tree per year. The whole quantity was suggested to be divided into three applications, that is, the first after-harvest (½N + ¼P2O5 + ¼ K2O +½MgO + all the compost); the second before-blooming (¼N + ½P2O5 + ¼K2O), and the third fruit development (¼N + ¼P2O5 + ½K2O +½MgO). In Thailand, Subhadrabandhu and Ketsa (2001) also proposed that fertilization for durian should be implemented based on growth stage. Correspondingly, the composition and amount of fertilizer applied after harvesting should be 15N–15P2O5–15K2O at 3–6 kg/tree, split to two applications at an interval of 3–4 months. Prior to flowering, durian trees should be fertilized with 3–6 kg/tree of 9N–24P2O5–24K2O in combi­ nation with foliar application of 10N–52P2O5–17K2O. At fruit development stage, fertilizer composition comprising high level of potassium should be used, for example, 13N–13P2O5–21K2O or 14N–14P2O5–21K2O at the rate

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of 1–2 kg/tree, divided to three times of application at an interval of 1 month. Similarly, in Darwin (Australia), Lim and Luders (2009) also suggested the three stages of durian fertilization based on leaf nutrient analysis and yield. Generally, a great amount of fertilizer should be applied immediately after harvesting to foster the vegetative growth. Subsequently, 1–2 months prior to flowering and the early stage of fruit development, a smaller of fertilizer could be used. Foliar fertilizers should also be applied at the early stages of vegetative growth. Durian growers in Queensland, Australia are advised to adjust nutrient inputs based on the yearly nutrient status of both leaf and soil as well as “nutrient budgeting” (Diczbalis, 2008), in which inputs of fertilizer are adap­ tive to removal of crop and response of the leaf. Ng and Thamboo (1967) stated that to obtain a fruit production of 6720 kg, durian trees had utilized from soil 18.1 kg N, 6.6 kg P2O5, 33.5 kg K2O, 2.6 kg CaO, and 5.4 kg MgO. Similarly, Diczbalis (2008) reported that for every ton of fruit produced, durian trees mobilized 5.7 kg K, 6.6 kg N, 33.5 kg K2O, 5.4 kg MgO, and 2.6 kg CaO. Adjustment of scheduling of fertilizer should also be based on crop phenology, nutrient requirement, and yield produced in the past (Lim and Luders, 2009). In addition, it is also necessary to consider the fluctuations of weather conditions which govern the seasonal changes of crop phenology. The latter were reported to be closely related to leaf and soil nutrient levels. For example, the content of all macro and microelements (particularly Zn and B) in durian leaves are declined during the stage of fruit set and develop­ ment. In addition, leaf N level is also lower during the active periods of leaf flushing. Soil N, P K, Ca, and Mg also show similar trends, namely, decreasing of levels during fruit development and active vegetative flushing (Lim and Luders, 2009). To increase the efficiency of inorganic fertilizer as well as yield and fruit quality, combining organic fertilizers with inorganic fertilizers is recom­ mended (Chau, 1997). In the MD and the Southeast region of Vietnam, growers are suggested to apply 10–20 kg/tree/year of organic fertilizer (Tri and Khoi, 2003). In addition, organic fertilizer also helps to enhance soil quality and reduce Phytophthora disease incidents. Biocompost amendment (10 ton/ha of cow dung and rice straw composted with Trichoderma sp.) helped to increase the soil organic matter, aggregate stability, labile organic nitrogen, available phosphorus, and improvement of soil microbial activity in durian orchards of the MD (Guong et al., 2011). Furthermore, gummosis/foot rot disease incidents were reduced, and root recovery from damage caused by Phytophthora was significantly improved. In addition, the incidence and

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severity of the disease were reduced by applying composted chicken manure and composted waste (Tri et al., 2001). 3.14 TRAINING AND PRUNING One year after planting, training should be implemented. Since most of durian clones are cauliflorous, the trees must be trained toward a main trunk with scaffold branches developing around it. To obtain the maximum yield potential, a balanced branch distribution is necessary. For a good vegetative growth, no pruning is necessary in year 1 to encourage the growth of main stem. In year 2, it is necessary to remove acute branches, and maintain 5–8 lateral primary branches in a balanced arrangement with the first level at about 75 cm above the ground. In year 3, to help develop and strengthen primary and lateral branches, the main stem height is cut down and kept at E coli > S faecalis > S aureus > P vulgaris > S flexneri (Dawkins et al., 2003). Extracts of ripe and unripe fruits had remarkable antibacterial activities on S. aureus, B. cereus, E. coli, P. aeruginosa, and S. flexneri, where it displayed small (0.2–0.3 mg/mL) MIC (minimum inhibitory concentration) for gram-positive bacteria and large (1.5–4 mg/mL) for gram-negative bacteria (Emeruwa, 1982). The petroleum ether extracts had high antimicrobial activity with 2 mg/mL MIC as against doses of 4–6 mg/mL for recognized drugs including perflacine and cefu­ roxime (Orhue and Momoh, 2013), 1% HCl and ethanol extracts exhibited antimicrobial activity over the gram-positive and gram-negative organisms, while the water extract was effective against E. coli and S. aureus (Orhue and Momoh, 2013; Rahmani and Aldebasi, 2016). 9.2 AREA AND PRODUCTION Papaya production occurs under tropical climate, and in mostly frost-free subtropical areas. Although it is a tropical crop, but it does well in a slightly

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tropical environment occurring at places of lowland, highland, and an altitude of 1000 m (Mishra et al., 2007). The production areas cut across the globe and cover about 60 countries, with most production coming from developing countries (Evans and Ballen, 2015). Although it can tolerate frost, the geographical spread is limited by frost, excessive dry weather and can be found even at an altitude of 1200 m a.s.l. (TNAU, 2015). Major areas of commerce and papaya production occur essentially between 23° N and S latitudes. Nonetheless, papaya cultivation has expanded to reach 32° N and S of the equator (Paull and Duarte, 2011). The major commer­ cial producing countries include India (providing 25% of world production), followed by Brazil and Mexico. Other countries include Nigeria, Australia, Hawaii, Thailand, South Africa, Philippines, Indonesia, and Taiwan (Mishra et al., 2007). The papaya production area has continuously increased in the last 50 years to a record of 438,239 ha in 2010 with Nigeria rated first and Indonesia second in the land mass (ha) established with papaya. The area cultivated with papaya in India, Brazil, and Mexico was moderate in the 1960s but has progressively increased, and India in 2009 was ranked first, while Brazil and Mexico were still ranked third and fourth, respectively, the area of land culti­ vated in both countries has decreased slightly in the last few years (Fuentes and Santamaría, 2014). With an estimation rate of 4.35% per annum during 2002 to 2010, the global papaya production in 2010 was put at 11.22 Mt. The production estimate from India was 4,713,800 t (38.61%), Brazil 1,871,300 t (17.50%), and Nigeria 703,800 t (6.79%). The production in 2010 has a 7.26% rise above that in 2009, and 34.82% higher than that in 2002 (FAOSTAT, 2012a; Evans and Ballen, 2015; FAO, 2016). The years 2009 and 2010 recorded the highest increase in global papaya production with improved production coming from India that recorded an increase by 20.50% due to improved production factors that include increase in planted area, improvement in plant genetics, and better handling and management methods (Evans and Ballen, 2015). Other countries playing important roles in papaya trade and production however mainly for papain production include Sri Lanka and Tanzania. 9.3

MARKETING AND TRADE

Most papaya fruits production in the tropics is faced with problems of high local consumption, nonexistent neighborhood markets, and inability

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to handle large consignments (Paull and Duarte, 2011). For many years now the demand for tropical fruits has witnessed a steadily growing market. Therefore, with the current production trend and trade of fresh tropical fruit a future increase in the world production figure is expected. In 2010, the world production turnout of tropical fruits (excluding bananas) attained the level of 73.02 million Mt, the total turnout of which about 98 percent was from developing countries, while 80% external trade was from developed coun­ tries (FAO, 2003). Through improved acceptance and demand, following mango (38.6 Mt or 52.86%) and pineapple (19.41 Mt or 26.58%), papaya production (with 11.22 Mt or 15.36%) has been placed third in the total tropical fruit production (Evans and Ballen, 2015). The annual papaya production turn-out estimation of top producing coun­ tries in the world includes India (5.5 million tons), Brazil (1.6 million tons), Indonesia (900,000 t), Nigeria (800,000 t), Mexico (800,000 t), Philippines (172,628 t), Dominican Republic (704,786 t), Democratic Republic of Congo (220,483 t), Venezuela (165,102 t), Thailand (157,571 t) (World Atlas, 2017; The Daily Records, 2018). Total area harvested in the world was 441,964, with area harvested in hectares for each country showing for India (133,000), Nigeria (97,838), Brazil (30,372), Bangladesh (22,000), Mexico (16,820), Congo (12,726), Peru (12,328), Mali (10,500), Indonesia (9980), and Kenya (8869). Although according to FAO (2016), the total world production was 13,050,749, with country production quantity for India (5,699,000), Brazil (1,424,650), Mexico (951,922), Indonesia (904,284), Dominican Republic (863,201), Nigeria (836,201), Congo Democratic (215,263), Cuba (212,579), Columbia (188,305), and Thailand (169,942). In 2009, with an estimated 31.5% that exceeded the previous volume exported in 2002 valued at about $197.2 million, the global papaya total export estimation was put at 268,476 Mt (FAOSTAT, 2012b). The three coun­ tries that included Mexico (41%), Brazil, and Belize (11% apiece) produced 63.28% of the global trade during 2007 and 2009, and therefore dominated the papaya export market. Other major exporting countries among papayaproducing countries include Malaysia, India, and the United States (mainly via re-exports). However, much of the harvest in many producing countries were consumed or traded locally (OECD, 2003; Diop and Jaffee, 2005). Unlike most other exporting countries, about less than 1% of the Belizean crop is expended locally (UN Comtrade, 2012). Marketing rules for trade are routinely the outcome of agreement between the shipper and the wholesaler or retailer (Paull and Duarte, 2011). The papayas that are transported by air are the ones that dominate the market, while those delivered by ship due to duration in transit may be

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unreliable. The substantial import markets for fresh tropical fruit include the United States, the EC, Japan, Canada, and China (Hong Kong SAR). The demand for Formosa papayas, one of the most common papaya varieties, is currently very high, especially in Germany and Netherlands. Due to excessive and cheap labor papain production is principally centered in Tanzania and India (Paull and Duarte, 2011). Most of the markets where papaya is traded, apart from size and appear­ ance, consumers’ interests are now shifted to making demands on higher quality with emphasis placed on aroma, flavor, and nutrient value. Other typical requirements include nonoccurrence of decay, breakdown, internal growth, and other forms of unwholesomeness. This indicates that produce must be free from injuries, including insect bites and mechanical injury (Paull and Duarte, 2011). With reference to combined factors such as local demand, environmental and management factors, a difference occurs between the structure of world fruit trade and that of the existing fruit production chiefly because many of the largest producers are not significant traders (Diop and Jaffee, 2005). Among those assets needed to succeed in fruit export include a conducive and favorable agroclimatic conditions, sufficient land and water resources that are easily accessible; an initial comparative advantage of an available inexpensive labor; and a collection of commercially experienced entrepre­ neurs, and these should be complemented by being physically located near the sea or close to a major market (Diop and Jaffee, 2005). Although in the presence of some or even most of these assets, requirements for appropriating and translating them into a sustainable and competitive horticultural industry with continued improvement in ability to compete over time would depend upon appropriate institutional structures and distinctive set of investments, supported by encouraging governmental policies, although not usually without the elements of luck (FAO, 2003). 9.4

COMPOSITION AND USES

The typical papaya fruit is comprised mainly of seed, pericarp/skin, and fleshy pulp at 8.5%, 12%, and 79.5% composition, respectively (Medina De La Cruz et al., 2003). The nutritional values (100 g edible portion only) consist of water 88.83–89.3 g, energy 123–163 kJ/(29–39 kcal), protein 0.4–0.61 g, fat 0.1–0.14 g, carbohydrate (total) 6.9–9.81 g, carbohydrate (sugar) 5.9–6.9 g, dietary fiber 1.8–2.3 g, cholesterol Nil, sodium 3–7 mg,

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potassium 140–257 mg, calcium 24–28 mg, magnesium 10–14 mg, iron 0.1–0.5 mg, zinc 0.07–0.3 mg, β-carotene 276–910 µg, thiamine 0.027–0.03 mg, riboflavin 0.03–0.032 mg, niacin 0.03–0.338 mg, vitamin C 60–61.8 mg (171% of RDI), and vitamin A Eq. (Papaya Seed Australia, 2007; USDA, 2006; OGTR, 2008). Sugar, the main polysaccharide component of papaya fruit, differs significantly in the quantity among cultivar type and agronomic condition. The Indian cultivars possess more sugar content (10–10.2% TSS (°Brix) than cultivars grown in the United States (5.6–7.1%) (Devaki et al., 2015). The composition range for papaya fruit and leaf include the followings: The fruit comprises of calories 23.10–25.80, moisture 85.90–92.60%, ash 0.31–0.66 g, crude fiber 0.50–1.30 g, crude protein 0.081–0.34 g, fat 0.05–0.96 g, carbohydrate 6.17–6.75 g, carotene 0.005–0.676 mg, thiamine 0.021–0.036 mg, riboflavin 0.024–0.58 mg, niacin 0.23–555 mg, ascorbic acid 35.5–71.3 mg, tryptophan 4–5 mg, methionine 1 mg, lysine 15–16 mg, and mineral elements including calcium 12.90–40.80 mg, phosphorus 5.3–22.0 mg, iron 0.25–0.78 mg. The leaf comprises of moisture 83.30%, ash 1.4%, crude fiber 1.0%, crude protein 5.60%, fat 0.4%, carbohydrate 8.3%, carotene 28,900 I.U., ascorbic acid 38.6%, phosphoric acid 0.225%, and mineral elements of calcium 0.406% (CO), iron 0.0064%, and magne­ sium 0.035% (Saran and Choudhary, 2013). The proximate content of dried latex comprises of moisture (17.76%), ash (7.00%), crude protein (57.24%), crude fat (5.21%), and crude fiber (0.67%) (Macalood et al., 2013). 9.5 ORIGIN AND DISTRIBUTION Papaya origins are rather uncertain; however, the crop is regarded as a native of tropical America from where it spreads to all over the tropical world (Purseglove, 1974). The highest level of diversity occurs in the Central America (Morshidi, 1996; Van Droogenbroeck et al., 2002). Notwithstanding, botanists agreed that it is native to the lowlands of Central America, and situated around southern Mexico and Nicaragua (Paull and Duarte, 2011). The Spanish explorer Don Franscisco Marin introduced papaya into Hawaii in the early 1800s from where it became a trade commodity crop of Hawaii in 1948 (Fitch, 2005). The papaya has become widely dispersed and spread across the tropics and the subtropical areas with warmer weather conditions (Villegas, 1997), and is now acclimatized in many regions (Morton, 1987).

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9.6 TAXONOMY AND BOTANY Papaya is a member of the Caricaceae family that included 6 genera and 35 species comprised of Carica (1 species), Jarilla (3 species endemic to Southern Mexico and Guatemala), Horovitzia (1 species), Jacaratia (7 species from South America) (Badillo, 2001; Van Droogenbroeck et al., 2004), Cylicomorpha, from equatorial Africa with two African tree species, and Vasconcellea (21 species) (Badillo, 1993, 2000). With exception of Cylicomorpha, all other members of the family are native to America (Scheldeman et al., 2011). The genus Carica are indigenous to tropical America and only three are of horticultural importance, namely, C. papaya, C. andamarensis (Mountain papaya), and C. monoica. The C. papaya L. is the most valuable species among the Caricaceae. With the exception of the monoecious species (V. monoica (Desf.), V. pubescens, and the polygamous C. papaya), the Carica and Vasconcella species are dioecious. Papaya has been described as a small unbranching plant, fast developing herbaceous perennial with latex in all part (Purseglove, 1974; Chay-Prove et al., 2000). Many light green palmately lobed leaves that emerge from the apical part of the stem form the canopy. The usually large leaves clustered at the crown are arranged spirally around the stem (Chan and Theo, 2002). In a 3/8 spiral phyllotaxy two leaves emerge every week at the apical part of the plant (Fisher, 1980) with a life span for 3–6 months (Jiménez et al., 2014). The biological keys to differentiating the cultivars include the leaf shape and size, leaf veins (central veins), lobe counts, stomata type and count, and structures of leaf wax, and leaf petiole color (Teixeira da Silva et al., 2007). The papaya fruits occur in clusters and are located directly under the leaf canopy toward the top most part of the trunk (Karunamoorthi et al., 2014). The 2–10 m tall stem trunk has girth that tapers with about 30 cm thickness at the ground level to about 5 cm at the top, is hollow, fibrous, straight, and smooth but is adorned by marks of previous leaves and fruits (Purseglove, 1974). The usually single-stemmed papaya trees when damaged or due to injury to the apical meristem or by cut-back may produce multiple branches (Purseglove, 1974; Villegas, 1997). The stem usually thins out and at higher heights becomes commercially unproductive and is cut down (Wall, 2006). Wood density is only 0.13 g/cm3. Most of the hardiness and strength in papaya stems comes from the internal organ arrangement comprising of the thick, single layer of secondary phloem, and the two sclerenchyma layers located directly inside the bark. The xylem is not firmly lignified and aids in storage of water and starch (Fisher, 1980).

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The root system is well formed, dense, extensive, but shallow (Purse­ glove, 1974; Orwa et al., 2009). The epidermis, cortex, and endodermis enclose a vascular bundle inside which in an alternate arrangement are the xylem and phloem poles. Although maintaining succulence, the cambium arranged in a concentric ring triggers secondary growth and root thickening. Secondary roots have abundance of branches emerging from the upper parts of the root. The whitish cream-colored roots contain no laticifers (Marler and Discekici, 1997; Carneiro and Cruz, 2009). Morpho-plasticity describes the capacity of plant roots to modify root morphology under varying soil environment (Zobel, 1992). The papaya roots are highly morphoplastic as plant grown on hill sides produces ascending root growth under favorable soil conditions. In line with morpho-plasticity root growth attributes of size, number, distribution, and orientation also change under different soil condi­ tions (Olubode, 2010a). Papaya flowers open early in the day at 7–9 am, and these emerge near the trunk apex. The flower may persist for up to 3–4 days (Jiménez et al., 2014). The tiny, yellow, funnel-shaped flowers may occur in single or clustered form in the leaf axil. The three types of flowers include the male, female, and hermaphrodite flowers. The female flowers (Plate 9.1b) with ovate-shaped ovary possessing large functional pistil with no stamens are 3–5 cm long; male flowers with 10 stamens in 2 rows occur in inflorescence on long panicles (Plate 9.1a); the occurrence of hermaphrodite flowers depends on the season and is larger than males (Orwa et al., 2009).

PLATE 9.1 Papaya male flowers (a) on inflorescence and sessile female flowers (b).

The pollinated female flowers develop into smooth-skinned green fruits which when ripen may possess yellow-orange to pinkish-orange flesh and a central cavity containing a thousand or more small-sized black seeds

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

(Karunamoorthi et al., 2014). Several varieties of papaya with varying fruit shapes and sizes and other growth attributes have been observed. The oval to round-shaped pulpy natured fruits are berries. Seed size varies as one gram may contain 20 air-dried seeds (FAO, 2007), or up to about 65–75 seeds (Dinesh et al., 2017). Planting of one tree per hole, 50–80 g seeds will be required per hectare. The seed attributes show a true embryo and fleshy endosperm with oblong and flat cotyledons (Dinesh et al., 2017). The fruits vary in shape and size, being cylindrical or pear shaped in hermaphrodite trees, and more round on female trees (Salunke and Desai, 1984). The fruit has a distinctive flavor and has been distinguished for its high carotene content. Seedless fruits may also occur while the weight of a single fruit could range between 0.5 and 5.0 kg. The two main types of papayas observed include the small-sized fruit usually weighing between 0.5 kg and 1 kg, and the large-fruited size weighing up to 4.54 kg (EDI, 2012). In commercial papaya production, dioecious plants are usually grown directly from seeds, and considerable variations in the progeny occur. Seeds are therefore collected from trees selected for size and shape of fruit, vigorous vegetative growth, early fruit setting, and low bearing height (Medina De La Cruz et al., 2003). 9.7 VARIETIES AND CULTIVARS Considering the complex genetic make-up of papaya and the open pollinated nature papaya rarely breeds true, hence lack uniformity in horticultural characters. Despite the lack of recognized cultivars, controlled pollination of selected plants can assist growers to maintain satisfactory strains (Medina De La Cruz et al., 2003). Selection of cultivar type depends on papaya utili­ zation and destination, either for local market in fresh fruit form, transport to distant market, to suit demand from consumers or for latex extraction (Olubode, 2010a). Generally, due to the fruit attributes of higher yields possessing excessive proteolytic activity of the raw papain, the female fruit of the dioecious cultivar is favored for papain extraction compared to that of the hermaphrodite (Madrigal et al., 1980). However, on the other hand, the hermaphrodite plants from solo group due to the mealy flesh and small inner cavity of the bulb-shaped fruits are preferred for fresh fruit production compared to fruits from female plants (Marin and Gomes, 1987).

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PLATE 9.2 Fruits of sunrise solo showing pointed tip and pink solo showing depressed tip.

Solo Sunrise (Plate 9.2) is a dominant papaya variety in the world trade. The variety has relatively small fruits, weighing 250–500 g. Fruit shape is not dependent on variety but on the sex of the plant carrying the fruit. Fruit from bisexual plant has pyriform shape, while those from female trees are usually roundish in shape. Ahead of marketing, selections are made for pear-shaped fruit as against fruits from female trees. Flesh of bisexual hermaphrodite Solo fruit has sugary taste with pleasant but distinctive flavor and aroma. Under proper management total soluble solids (TSS) may range between 12–17% having a mean brix of 15.5% (OGTR, 2008). 9.7.1

IMPORTANT VARIETIES/CULTIVARS

Coorg Honey Dew, gynodioecious selection from honey dew that bears medium-sized dark-colored fruit weighing 1.5–2 kg. The plant has no male plant; the female and bisexual types appear in uniform distributions; the hermaphrodite tree produces elongated and oval fruits; female has ovoidshaped fruits. Kapoho Solo, formerly a Dwarf Solo, is pear-shaped, weighs 400–800g, has yellow skin and pale-orange flesh. It was a back-cross of Florida's Betty and Solo. Santa Cruz Grant, mainly bisexual, is a very large fruit weighing 4.5–6.8 kg, with yellow flesh of firm texture and a pleasant flavor. It has problem of marketing fresh because of fruit’s large size but can be prepared both ripe and unripe. Cedro is a dioecious heavy bearer, weighs 1.37–3.6 kg, has firm, yellow, melon-like flesh. It is highly resistant to anthracnose and is suitable as fresh fruit or for processing.

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

Singapore Pink, bisexual, cylindrical pink fleshed fruit, weighs 1–3 kg, has bright-yellow skin and thick, firm textured flesh. The fruits must be picked and sold in the mature unripe state, having problem with anthracnose during rainy period.

PLATE 9.3 Papaya trees showing the Jumbo (a) and Dahomey long (b) varieties in the field.

Solo, Golden Surprise, Hawaii, and No. 5595 are dioecious exotic culti­ vars mostly grown by farmers in Ghana but which after several generations lost their identities through cross pollination with local types (Medina De La Cruz et al., 2003). Similar incidence in Nigeria occurred with hermaphrodite cultivars “Sunrise solo,” “Pink solo,” and dioecious cultivars Homestead selection (NIHORT, 1982). Jumbo and Dahomey large (Plate 9.3) are vari­ eties introduced from nearby localities in Togo. US, Redlady, Mountain, Papayi, Apoyo, Local, Sunrise, Kiru, Solo, honey dew, and Sunsise solo are grown in Kenya. These are grown alongside wild relatives like naturally occurring Vasconcella spp. that grow on Kenya highlands, and listed among the local germplasm (Asudi et al., 2010). Homestead selection (Plate 9.4a) has a large berry fruit that weighs between 850 g and 3 kg, is 15–30 cm long, ovoid-oblong to nearly sphericalshaped, with smooth skin, firm, yellow flesh color with a large hollow internal cavity. The surface has funicles which are grooves that run the length of the fruit (NIHORT, 1982). Sunrise solo (Plate 9.4b), pear-shaped fruit, with slight neck, smooth skin without depression, reddish-orange firm textured flesh, sweet and sugary,

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with average weight 300–350 g. Seed cavity is not deeply indented. The fruit is of relatively small size of 12–14 cm long, 6–9 cm wide, 300–600 g. Eksotika fruits are small to medium size, average weight 400–800 g, with high sugary taste (12–14°Brix), orange-red soft textured flesh with an acceptable aroma, but do not keep well. The susceptibility to fruit freckles and malformed top disease affects its acceptance in commercial production (TFNet, 2018). Hortus Gold, a dioecious variety from South Africa, round-oval shape, sweet flavored, good textured golden-yellow flesh, weighs 0.9–1.36 kg, with slight beak at the apex, but becomes mushy when overripe, and is the only known papaya clone mainly propagated by leafy cuttings. The clonal variety has an advantage in the greater uniformity in the sex-linked fruit shape (TFNet, 2018). SunUp, the world’s first transgenic papaya modified with coat-protein moderated resistance to papaya ringspot virus disease, while Rainbow from a cross between SunUp and the Kapoho was the first transgenic commercial variety developed in Hawaii (TFNet, 2018). Vasconcella (Carica) pentagona or Babaco has parthenocarpic fruits that are exclusively clonally propagated by cuttings and is grown to a minor area in Ecuador and New Zealand (TFNet, 2018). 9.8 BREEDING AND CROP IMPROVEMENT In most papaya-breeding programmes, common breeding goals are observed across regions. However, specific objectives are noted for different regions with considerations to dictates from prevailing weather/climatic condition, consumer choice, sex types, and export trade (Paull and Duarte, 2011). Papaya is an open pollinated species, but self fertilization does occur. The absence of inbreeding depression gave rise to opportunities for the use of inbred strains to insert beneficial genetic characteristics into both gynodioe­ cious and dioecious lines (Aquilizan, 1987). The considerations for breeding program include the elimination of the prevalent sex-related summer infertility and stamen deformities (Giacometti, 1987), the cutback of papaya petiole (75–100 cm) to produce Solo line with short petiole (45–60 cm) for possible use in high density planting of papaya (Mishra et al., 2007), as well as production of strains identified for disease resistance, improved yields, and higher fruit quality and traits identified for improved performances under storage conditions (Nakasone and Paull, 1998). The adoption of

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biotechnological approaches such as embryo rescue and genetic engineering as opposed to conventional breeding can help overcome the limitations in transfer of useful traits encountered in papaya improvement programmes. These limitations include several postzygotic incongruities such as embryo abortion, poor seed viability, and sterility in progeny obtained following hybridization between two genera (Manshardt and Wenslaff, 1989). Observations among dioecious species revealed that male plants often exceed females in morphological characters and frequencies in populations (Dickson, 1991; Obeso, 2002; Marchin, 2006). Notwithstanding, taller female trees were reported for Homestead selection while no significant differences among sexes were reported in Sunrise solo (Ajiboye, 2015). More often than not, for topmost plant species, stressful conditions lead to the presence of more male than female flowers while the reverse is the case under favorable conditions (Meagher, 1988; Davenport, 1990; Albrigo and Sauco, 2004). The occurrence of labile sex is more common among dioecious and monoecious plants than among hermaphrodites due to environmental stress that concerns light quality/quantity, nutritional issues, vagaries of weather or drought/ insufficient moisture conditions which often favor maleness (Korpelainen, 1998). The regulation of sex expression by plant hormones indicates an equilibrium between hormones promoting sex expression where gibberel­ lins normally stimulate maleness, while auxins, cytokinins, and ethylene are linked with appearance of female flowers (Jaiswal et al., 1985; Meagher, 1988). The female trees differed from male trees in the defence-related elements assembled in latex (Macalood et al., 2013), while no convincing reports were observed on linkage between sex and morphological character (Ajiboye, 2015; Olubode, 2010b; Olubode et al., 2016b). Nonetheless, specific genes or markers have been successfully applied to papaya production (Parasnis et al., 2000) which have assisted in sex identifi­ cation at the seedling stage (Collard et al., 2008). Several male-hermaphrodite specific markers were singly evolved by random amplified polymorphic DNA (RAPD) or amplified fragment length polymorphism (AFLP), and to differentiate between hermaphrodite and female papaya seedlings were metamorphosed into sequence characterized amplified region (SCAR) markers (Deputy et al., 2002), male-specific SCAR marker (napf) (Chan et al., 2003), and papaya sex determination marker (PSDM) (Urasaki et al., 2002). The main disadvantage to the use of these PCR-based sex-diagnostic methods includes the requirements for modern and sophisticated laboratory facilities and equipment, and the difficulty to perform these tests especially for field-based operations (Rigano et al., 2010).

Papaya

PLATE 9.4

635

Papaya trees in the field showing Homestead selection (a) and Sunrise solo (b).

Some of the most significant problems to papaya production worldwide include those virus-related problems like papaya ring spot virus (PRSV) and papaya leaf curl virus (PaLCuV), and fungal-related problems such as foot rot and fruit anthracnose, sex-linked problems such as stamen defor­ mities and summer infertility (Mishra et al., 2007). There is an absence of genetic resistance to PRSV in Carica papaya; nonetheless, some lines with PRSV tolerance have been used to insert the trait into some cultivars such as “Cariflora” (Conover et al., 1986). This possibility of tolerancebreeding program has provided opportunities for sensible fruit production by farmers even when plants are infected with PRSV, which has enabled farmers profitably harvest quality fruit produce and seeds (Prasartsee et al., 1998). Some species in the genus Vasconcellea with positive traits can be employed in papaya development programmes. Except for problems of genome incompatibility with those recognized with protection against PRSV crossing these lines with papaya to obtain protected interspecific hybrids have been attempted (Magdalita et al., 1997; Drew et al., 2005). Among these only Papaya × quercifolia hybrids have shown promising levels of fertility and hence have possible adoption in back-cross­ programmes (Sajise et al., 2004). The possible use of molecular markers to describe PRSV protection levels in Vasconcellea species will be of high benefit in the transfer of this trait into papaya (Dillon et al., 2005a, 2005b).

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9.9 SOIL AND CLIMATE 9.9.1 TEMPERATURE/RAINFALL REQUIREMENT The papaya plant as a tropical species is reported to be frost sensitive, thus requiring high heat degrees for optimum growth, development, and ripening of fruits. The optimal conditions for good growth and development occur in the range between 21 and 33°C, high annual rainfall with adequate spread in the range of 1500–2500 mm, at elevations below 900 meters. The papaya nonetheless can also survive as high as 2100 m near the equator (PFAF Plant Database, 2012). The papaya grows well and faster in warmer regions, with fruits of better quality than obtainable in regions with cooler condi­ tions (de Siqueira and Botrel, 1986; Medina, 1989; Oliveira et al., 1994). Moreover, temperature influence is well marked on germination through vegetative growth phase to the onset to full reproductive development (floral initiation, fruit set, and fruit maturity) (Atwell et al., 1999). Hence, a drop of temperature below 15°C has an adverse effect on tree growth; thus, cessation of flowering and delay in fruit maturation happen, and as leaves are shed sunburn of exposed fruit occurs (Marin et al., 1995; Almeida et al., 2003). In the concept of heat requirements or degree days, also called thermal units, the baseline temperature is that below which the plant fails to develop, thus indicating a linear association between temperature ranges, plant growth, and development (Almeida et al., 2003). A baseline temperature therefore occurs for every plant species or cultivar the value of which varies with plant age (Almeida et al., 2003). 9.9.2 SOIL QUALITIES Soil qualities influencing the nutritional well-being of crops are varied which include soil pH, available soil nutrients, soil textural qualities, organic matter content, and plant–soil water relationships (Hornick, 1992). The plant can thrive on a varied type of soil, where drainage is regarded as the utmost essential requirement. In consideration of drainage, loam or sandy loam soil is the choice soil while soils with poor drainage like heavy clay soils should be avoided. A short lifespan occurs under poorly developed root system while poor drainage conditions can lead to the occurrence of root and collar rot diseases (Paull and Duarte, 2011). However, papaya can be successfully managed on different soil types. The addition of organic matter has stabi­ lizing effects on sandy soils and clayey soils. In sandy soil large amounts of organic matter and high fertilizer application (8 kg/plant/year) coupled with

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irrigation would be required, while stabilizing effects on clayey soils allow improved soil texture, percolation, and porosity. Drainage is required in peat soils since the water table is usually high and other alluvial soils along streams and canals. In these soils because of poor anchorage and stunted root growth there is a tendency for lodging once fruiting commences. High liming application rates (6–8 t/ha) are therefore essential for cultivation with additions micronutrients (boron, zinc, and copper) to ensure high-quality production on the soils. Boron deficiency and nematode infection are two major difficulties experienced on sandy soils. Suitable soil pH should range between 5.0 and 7.0 (Paull and Duarte, 2011). Liming is required in soil with pH range of 5.0–5.5 to increase growth and yield. Papaya can virtually be successfully grown on varied types of problematic soils. 9.9.3 MOISTURE AVAILABILITY The attribute that qualifies fruits as perishable is the moisture content. In the growth and development, each developmental phase of a fruit is moisture sensitive, howbeit with different degrees of moisture sensitivity (Aiyelaagbe, 2013). Since the life cycle is cut across different seasons including the dry season under rain-fed condition, papaya crop at one time of its growth dura­ tion is exposed to soil moisture stress which could have serious destructive and retardation effects on growth, development, and yield (Aiyelaagbe, 1988; Asoegwu and Obiefuna, 1985; Oseni, 1984; Maurya, 1986). Every growth stage for papaya plant from vegetative (seed germination, seedling growth, vegetative growth) and reproductive (flowering through fruiting phase) has critical water potential reported as -0.01, 0.02, -0.02, -0.20, -0.20, -0.02 MPa, respectively (Aiyelaagbe, 1988). Soil moisture depletion below -0.02 MPa soil water potential achieved by watering every 11th day retarded growth of nursery stage “Homestead selection” papaya seedlings and delayed attainment of transplantable size (Aiyelaagbe and Fawusi, 1996). Moreover, imposition of drought stress by reduction in water availability at the fruit set stage caused retardation effects on leaf area, total dry matter accumulation, fruit set, and yield of field grown “Homestead selection” papaya (Aiyelaagbe and Fawusi, 2000). Marked reduction in water availability in the soil tends to limit flowering/ bud initiation in many fruits, while limited water stress may, in certain plants such as citrus, be conducive for flower initiation. Both leaf and flower drops are common in papaya under pronounced moisture stress or unavailability of soil water (Rice et al., 1987). Differential responses were observed in

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seed germination where what is insufficient for one is excessive for others; thus, 6–9 days before watering adversely affected germination of “Home­ stead selection” papaya seeds but enhanced the germination of “Allahabad Safela” guava (Psidium guajava L.) (Aiyelaagbe, 1988; Aiyelaagbe and Fawusi, 1988). The replacements of 120% ETo resulted in highest growth, development rates, and highest yield potential for papaya trees, while the lowest yields were verified for replacements at 40% and 60% of ETo (da Silva, 1999). Excluding optional irrigation, prevailing rainfall condition should ensure a well-distributed monthly minimum rainfall of 100 mm. However, papaya would require application of light and frequent irrigation when dry weather persists (Paull and Duarte, 2011). 9.9.4 IRRIGATION REQUIREMENT Juvenile trees require about 0.3–0.5 pan evaporation while for highest yield of grown-up trees 1.25 pan evaporation is required. The require­ ment is to replace at least the moisture lost by pan evaporation. The wet season requirement for good production is in the range of 60–90 l/ tree/week following after planting, while the dry season planting will require 120–240 l/tree/week (Paull and Duarte, 2011). Irrigation can be at intervals of 10–15 days to sustain production and applied by flooding along the row spacing using furrow application on both sides or by the use of micro sprinklers, jets, or drip. The use of overhead sprinkling is not recommended because papayas are wind-pollinated, and overhead sprinkling negatively affects dispersion of pollen. The use of drip system should be targetted toward delivery of maximum amount rather than average demand. If a tree requires an average of 56 l water/day but 114 l maximum during the dry season, the drip delivery system capacity is targetted toward the maximum requirement. The use of one emitter per tree is sufficient for the first 3–4 months growth, after which two emitters positioned at each side of the tree will be needed. Nonetheless, a single micro-sprinkler (30 L/h) is also sufficient to meet the plant demands (Paull and Duarte, 2011). 9.10

PROPAGATION AND ROOTSTOCK

Conventionally, papaya is normally propagated by seed which for economic reason is less demanding due to an abundance of readily available seed compared to other practically available asexual methods (cuttings, grafting,

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and tissue-culture) which are more or less labor intensive and expensive (Saxena et al., 2016). Exceptions to this rule include the clonally propagated Hortus Gold that does not breed true from seed, and Vasconcella (Carica) pentagona or Babaco, which are solely raised by cuttings. Each papaya fruit has 300–700 seeds and there are approximately 20,000 seeds per kilogram. Seeds are processed by washing to remove the gelatinous aril, and air dried ahead of sowing and the fresh seeds normally germinate within 2–3 weeks (Vandenabeele, 2014), treated with fungicide and sown immediately since seeds may lose viability in storage (Medina De La Cruz et al., 2003). A significant constraint in papaya production is dioecious character of the plant, and the occurrence of the numerous pollens carrying male plants that are unproductive in the collection (Singh et al., 2010b). A clonal propagation technique using mature female plants is therefore extremely advisable for trade activities, especially in subtropics where some dioecious lines produce better than hermaphroditic ones. Application of cytokinins and auxins at a proper ratio results in both the shoot and root formation (Singh et al., 2010b). Nonetheless, performance of IBA was better for root induction in papaya shoots regenerated (Bhattacharya et al., 2002), compared to induction of root formation using IAA which results in poor root development. Propagation of papaya by seed is hampered by many problems among which is harvest season which affects seed quality (Tokuhisa et al., 2007a); postharvest storage of fruit (Martins et al., 2006), the seed formation surrounded by a gelatinous sarcotesta, and its content that has inhibitory influence on germination (Tokuhisa et al., 2007a, 2007b). “Sunrise Solo” seeds with lower density seeds exhibit abnormal embryos (Nagao and Furutani, 1986). At advance postharvest maturity of fruit, seeds attain physiological well-being with an attendant reduction in dormant and nonvi­ able seeds. The physiological quality was also high for seeds extracted at the fifth (75% maturation) and final maturation (100% maturation) stages (Dias et al., 2014). However, the use of X-ray test has proved adequate in the assessment of structural well-being of papaya seed thus distinguishing between empty seeds and those with normal embryos (Dias et al., 2014). Seeds are raised in growing media using steriled soil heated at 200°F in an oven for 1 h using 50:50 soil:vermiculite. This offers protection from damping off disease and hence prevents high mortality rate in young papaya seedlings. Seeds germinate in 10–14 days, but may drag to 3–5 weeks. Germination can be hastened in some seasons by the application of Gibberellic acid. The seedlings are transplanted at the onset of rains when they are about 2 months old (40 days) after seed germination. The seedlings

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begin flowering at 9–12 months after they germinate (Medina De La Cruz et al., 2003). Nonetheless, the problems encountered in physiological well­ being of seeds causing nonuniform and slow germination remain pending in papaya propagation. 9.11

LAYOUT AND PLANTING

There are commercial seed centers offering viable seeds for growers. The hermaphrodite trees exhibit per hectare a ratio of 1:2:1 male to female to hermaphrodite, respectively, in the field, and in dioceous trees a ratio of 60:40 male:female, respectively (Purseglove, 1974; Olubode et al., 2012a). Hybrids have more fruits and have consistent fruit shape and size, and are less susceptible to disease. In bisexual plants, fruit observed on hermaphro­ dite trees is often influenced by prevailing ambient temperatures leading to low yield and/or deformed fruit (OECD, 2003). Under the monsoon climatic types or environment with distinct wet and dry season, targeting the rainy season is ideal. Seeds from freshly harvested papaya fruits after processing (Plate 9.5) are sown into propagation bags beginning from late dry season to early part of each new year. The seed rate is attained using two seeds per bag in the nursery where they remain till after germination when at two months old, they are transplanted into the field.

PLATE 9.5 Papaya seeds under processing.

The cultural practice of preparing lands before field transplant occurs at the onset of the rains of each new year, where field work of cultivation with plough and harrow is performed to obtain a crump soil and near leveled field.

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The fields are thereafter demarcated into blocks for the ease of field manage­ ment. The blocks and plant stands are pegged out, and planting holes are dug at intervals of 2 m × 2 m or 2.5 m × 2.5 m (rarely 3 m × 3 m) standard spacing for papaya (Purseglove, 1974). The set time for nursery establishment is determined by the type of production methods either for normal rain season or under irrigation for dry season. Seeds treated with fungicide (optional using Thiram (TMTD) W.P.) are normally sown into nursery and take 2–4 weeks for emergence subject to influence of temperature. The seedling transplant is done into 60 × 60 × 60 cm sized planting holes already packed full of top soil mixed with 20 kg farmyard manure, sometimes with additional materials like neem cake (1 kg) and bone meal (1 kg). Seedlings are watered a day ahead of transplanting date which, if done on wet day or late afternoon, could minimize transplanting shock and seedlings are watered immediately after transplanting. Compatible intercrops such as bush greens, Jews’ mallow, okra, cucumber, and scarlet eggplant, including leguminous crops, have been recommended for intercropping but with caution of no intercrops during the critical period of flowering phase (Aiyelaagbe and Jolaoso, 1992; Olubode et al., 2012a, 2012b). The papaya cultivars displayed distinct but different plant architecture that changes with seedling age and with crop requirement in their response to the environment (Olubode et al., 2014b, 2016a). Despite this, most recom­ mendations for spacing considered monoculture conditions but cultivation of papaya in polyculture systems adds complications that could possibly have a significant influence on their performances, production, and productivity. Crop performances to five spacing tested on papaya cv. Coorg Honey Dew (2 × 2 control, 1 × 1, 1.5 × 1.5, 2.5 × 2.5 and 3 × 3 m) showed significant response with 2.5 × 2.5 m spacing on growth and flowering attributes and fruit set characters (Singh et al., 2010a). Among the six varieties that were evaluated only the Amrita and Coorg Honey Dew were found to be superior over other varieties (Gunnannavar et al., 2017). In the same manner Meena et al. (2012), Das and Dinesh (2014) observed maximum plant girth in cv. Sunrise solo (37.77 cm) and minimum girth in Pusa Dwarf (29.23 cm) variety. Although plants with thick stem will have good plant spread with big-sized fruits, higher plant spread will reduce the number of plants per unit area. Hence, selection for high-density planting trees with medium-sized or stem diameter with less spread is desirable. High-density planting (HDP) is a recent concept of increasing yield and output without effect on fruit quality. HDP strategizes on maximizing number of the plant per unit area to get the maximum yield per unit of tree

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volume without adverse effect on soil fertility status (Saroj and Singh, 2018). This is generally achieved by controlling the tree size or through an improved planting system (Plate 9.6). The tree growth can be managed using dwarfing scion cultivars, dwarfing rootstocks, choice of inter-stock, use of growth hormones, inoculation with exocortex viroids, dwarfing methods with approach of rootstock incompatibility, and/or genetically dwarf scion cultivars etc. Considering relative plant height and agronomical factors, planting densities may be categorized as low-density planting (LDP), medium-density planting (MDP), high-density planting (HDP), and ultradensity planting (UDP).

PLATE 9.6 Papaya tree sizes showing dwarf (a) and tall (b) types.

For HDP plantation, some techniques and tips are usually observed as new approaches to pruning, thinning, harvesting, etc. (Saroj and Singh, 2018). The advantages are such that it shortens juvenility, provides efficient use of resources, and the dwarfing technique is an efficient way of increasing plant population per unit area, and thereby guarantees an early production and return per unit area (Mishra and Goswami, 2016). The HDP approach has been found suitable for some tropical and subtropical fruits, namely, mango, guava, and papaya with corresponding densities of 1333, 5000, and 6400 plants/ha, respectively (Mishra and Goswami, 2016). Papaya varieties planted using a spacing of 1.25 × 1.25 m (6400 plants/ha) had a fruit yield of 103 t/ha (Ram, 2005). HDP plants at closer spacing in the double row arrangement had the narrowest stems which were bent outward and instead of perpendicularly positioned to the ground compared to the stable conditions under wider

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spacings. The double-row planting guarantees advanced planting densi­ ties, adequate space, and water use efficiencies. Drip irrigation technology applied to widely spaced plants contributes immensely to meaningful use of water, thereby assisting in enhancing use of agricultural lands in semiarid areas. The most efficient use of water, mulch techniques, and the double-row concept that include closer double-row spacing is an environmentally sound farming practice that increases economic benefits from production and results in more economical gains for tropical farmers (Zimmerman, 2008). 9.12 VEGETATIVE GROWTH AND DEVELOPMENT The average leaf output under tropical and subtropical conditions was approximately 1.5–2.2 per week, while flower development from emer­ gence to anthesis was averaged over 10 weeks (Sippel et al., 1989). Unfa­ vorable environmental conditions impose different levels of stress causing significant changes in the plant growth responses, organs growth, and fruit setting rate (Cosmulescu et al., 2008). Different architectural display was observed among three morphotypes, sourced from Homestead selection and Sunrise Solo cultivars. Homestead selection morphotypes had more vigorous growth exhibited by taller and wider plants, more numerous leaf production, and longer petiole, compared to observed response from those of Sunrise Solo with thicker base and greater leaf angulation (Olubode et al., 2014b). Moreover, cultivation of papaya varieties and papaya intercropped with vegetable crops showed the influence of below ground rooting activi­ ties of papaya affecting the soil bulk density (Olubode et al., 2013). Crop growth depression at the physiological transformation from vegetative to reproductive growth of flowering/fruiting was reported in Homestead selection but not in Sunrise Solo (Aiyelaagbe et al., 1986; Olubode and Fawusi, 1998). The orthogonal analysis confirmed by the PCA correla­ tion relationships performed on seasonal effects of pronounced drought conditions separating wet and dry seasons, revealed that most of the times the juvenile papaya had no influence on the responses observed at mature papaya stage (Olubode, 2019). 9.13

NUTRIENT MANAGEMENT

Over the last 30 years, the average annual depletion rate observed for cultivated lands in selected African countries was 22 kg N, 2.5 kg P, and 15 kg K per hectare (Koohafkan and Altieri, 2010), necessitating a balanced

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nutrient supply targeted toward obtaining sustainable production of higher and regular yields and also for optimizing an improved shelf life (FAO, 2008; Singh et al., 2010c). The world’s total fertilizer demand in 2013 was 183 Mt, although the estimated total fertilizer production capacity was 278 Mt out of which a total of 237 Mt was supplied (FAO, 2016). The fertilizer scale of demands indicated that production was sufficient for crop production. Despite the importance of chemical fertilizers in provi­ sion of easily accessible nutrients for plants, there have been problems of utilization in the tropics due to problems of high cost and relative scarcity, while their application increases soil acidity (Adedokun and Aiyelaagbe, 2008). There has therefore been an increasing interest in eco-friendly and sustainable agricultural practices (Malus´a et al., 2012), such as the use of microbial biopesticides and biofertilizers. The interactions of papaya plants with mycorrhizas for their water and nutrient uptake have been reported. There soil rhizosphere is rich in diversities and abundance of highly efficient microbes, among which is arbuscular mycorrhizal fungi (AMF) that play important roles in the nutrition and productivity of most tree crops (Oruru and Njeru, 2016). The important AMF reported to be associated with papaya roots are observed among the four to five genera and 11 species among which Glomus, Acaulospora, and Gigaspora are found (Walsh and Ragupathy, 2007; Khade et al., 2010). The adoption of microbial-based formulations as bio-fertilizers can serve as a cheap and sustainable means to maintain soil fertility in smallholder farms. The cost of initial inoculum could be high and daunting, however, supported by low-cost multiplication technologies as an on-farm approach could assist to lower the cost. The positive effects of AMF on papaya have been reported (Sukhada, 1992; Khade and Rodrigues, 2009), but such information reported only the effect of phosphorus solubilizing microorganism. Endophytes inoculated papaya seeds (20 h at OD550 = 0.5) exhibited retarded germination and initial moderate seedling growth which improved after 3 months. Papaya inoculation with Pantoea, Microbacterium, or Sphingomonas spp. exhibited improved root and shoot growths (Thomas et al., 2007). G. mosseae had greater influence causing improved plant growth, fruit yield, and higher P and Zn contents than plants with G. fasciculatum. Nonetheless, for both fungi total soluble solids (TSS) exhibited slight increase at the 75% P level (Mohandas, 2012).

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The growth habit of papaya plant described as a high nutrient exhaus­ tive fruit crop (Olubode et al., 2016a), and the all-year round fruiting habits necessitate the need to sustain the good growth and production with periodic adequate nutrient supply (Paull and Duarte, 2011). Notwith­ standing, most papaya varieties exhibited similar nutritional requirements (Olubode et al., 2013). In the nutritional status of papaya, the determination of P, Ca, and Mg status was reported as best using the leaf blade tissue, the petiole was best for K, and both leaf and petiole were adjudged as best for N status, and the best sampling time was 3 months after flowering (Badole and Nikas, 2016). In general, for most crops adequate supply of nitrogen and phosphorus during the early growth stages is advocated for optimum growth and organ development. Nonetheless, the fruiting stage require­ ment necessitates higher rate of potassium but lower application of phosphorus, due to fruit size retardation effect of excessive phosphorus rate. The continuous foliage output rate from juvenile and mature stages justifies the provision of high nitrogen rates to support consistent growth (Paull and Duarte, 2011). The supply of organo-mineral fertilizer (OMF) to papaya orchards had significant influence leading to lower soil bulk density (SBD), and in post cropping soil analysis had higher % P, % K, Na, and % organic matter compared to applied inorganic fertilizer NPK which lowers Na. Fields planted with sole papaya had higher SBD than those with papaya crop mixture. The more rooting activities under homestead papaya resulted in lower SBD and significantly lower % organic matter compared to plots under sunrise crop mixture which recorded lower Na and Mg (Olubode et al., 2013). Diverse elements of production, such as soil-based problems, vaga­ ries of weather, and cultural practices affecting locations, require that specific production packages be adopted for such locations/areas as products of plant nutritional responses that are derived from soil and plant foliar analyses. Recommendations for plants grown especially in sandy loam soils include an initial pre-plant supply of complete fertilizer (5:7:4) at 0.5 kg, with a dose of 0.25 kg of SSP added with 1.0 kg of lime per plant. At the post-plant growth stage, a 2-monthly application of complete fertilizer (10:2:16) at 100 g/plant is recom­ mended, with monthly dosage of 150–200 g per plant during summer and autumn. In the year two of production, a dosage of 250 g per plant is applied at 2–3-monthly intervals. The sandy soil sensitivity of papaya to boron deficiency is well noted and requires application of borax applied by soil or foliar application at the recommended rate for

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

each location. In year one of growth, application rate of 20 g of borate at 3–4-monthly intervals is recommendable, while 30 g/plant could be applied at the second year of cultivation at 7–8-monthly intervals (Paull and Duarte, 2011). Fertilizer recommendations for optimum papaya fruit yield include 50 g/tree/month of NPK (15–15–15) (Adelaja and Olaniyan, 2000). The applied rates of 250 g N/plant and 150 g P2O5/plant resulted in fruit yields of 38.21 and 39.51 kg/plant, respectively, in “Sunrise Solo” (Jayaprakash et al., 1992). The fruit yield responses, petiole N content, and water use efficiency had superior responses for an applied rate of 450 g above that of 150 g N/plant in cv. Coorg Honey Dew (Srinivas and Prabhakar, 1993). Depending on various factors such as cultivar type, production site/location, and the pre-plant fertility status of the soil, plant nutritional requirement for improved yield and fruit quality for N, P, and K will vary from 140–375 g/plant, 70–340 g/plant, and 140–600 g/plant, respectively (Kumar et al., 2010).

FIGURE 9.1 Soil average temperatures as observed under papaya in crop mixtures with okra and cucumber vegetables (H = Homestead selection, S = Sunrise solo).

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Organic agriculture relies on production methods of crop rotation, soil building, and biological pest management (UNCTAD, 2003), which includes sustainable agricultural practices that utilize natural (nonsynthetic) nutrient recycling processes to sustain or regenerate soil quality. These include the use of live mulch, organic manures, compost, crop rotation, and polyculture (Badgley et al., 2007). Most organic farms therefore in order to increase productivity of organic fruits and vegetables and lessen environmental degradation rely heavily on the intensification of sustainable farm manage­ ment practices that make use of the readily available renewable resources, ecological stability, and biodiversity (USDA-NOP, 2009). The use of chlorine by organic processors and shippers is regulated to within specified limits at 4 mg/L (ppm) which is in conformity with the Maximum Residual Disinfectant Limit under the Safe Drinking Water Act (Suslow, 2006; Silva, 2008), likewise all liquid sodium hypochlorite (a source of chlorine), granule forms of calcium hypochlorite, and chlorine dioxide are included among the controlled materials by organic standards (Uthairatanakij and Jitareerat, 2015). Organic production methods using available organic fertilizer in the form of city wastes, animal wastes, and industrial products in the form of organo-mineral fertilizers are often employed as soil amendment materials. The comparably cost-effective and relatively safe organic manures support crop production systems by reason of improved nutrient recycling and soil health affecting properties such as the physical, chemical, and biological status of the soil and thereby impact reasonably the long-term benefits to the soil structure and water holding capacity (Ojeniyi, 2000; Gambo et al., 2008; Aruleba and Fasina, 2004). The optimum yield under organic production system was attained with 10 t/ha of a fortified “Type A” OMF (Olubode et al., 2013), although Odeyemi et al. (2015) reported an optimum at 20 t/ha using Sunshine organic' fertilizer, equivalent to an earlier report by Olubode and Fawusi (1998) that observed the 20 t/ha poultry manure as optimum. The positive influence of OMF on post cropping soil fertility status showed a moderation of the soil acidity levels caused by the increased Ca and Na addition to the soil (Olubode et al., 2013). However, the relative inadequacy of OMF in supplying soil nitrogen and phosphorus suggested the lack of significant effect of OMF on the post cropping soil fertility status. The relatively improved performance of papaya when supplied with OMF compared to mineral fertilizer could be adduced to the availability of micronutrients which were not nonexistent in the NPK (Olubode et al., 2013).

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

Soils under organic manure production system exhibit maximum presence of microbial population (bacteria, fungi, and actinomycetes) and activities of soil enzymes (urease, phosphatase, dehydrogenase, and cellulases) compared with that under recommended inorganic fertilizer rates, with significant positive association observed in soil supplied with compost (Ravishankar et al., 2010). During reproductive stage of improved papaya varieties, the demand for P exceeds the capacity of the root system (Dunne and Fitter, 1989), which agrees with the description of papaya as a high nutrient demanding crop (Olubode et al., 2016a). In the natural ecosystems, plant interacts with many microorganisms to satisfy their water and nutrients requirements, but the effect is not seen because of the relative inadequacy of those soil microorganisms (Miransari, 2011). Thus, it is imperative to select the best microbial combinations to use to optimize organic production systems. The indication therefore is that without fully depending on chemical fertilizers it is possible to encourage healthy cultural systems to assist in better productivity and ecosystem conservation (Pandey and Chandra, 2013). 9.14 TRAINING AND PRUNING Papaya plant is single stemmed with a terminal growing point. The plant is usually not pruned except if wounded or damaged, and multiple stemmed trees do not produce as well. The usual practice is to prune away side shoots observed in some cultivars during their juvenile stages. In such cases the shoot nearest the apex is maintained to reestablish the tree. Mostly, pruning is limited to removal of lower leaves to facilitate harvesting, or allow access of spray materials (Paull and Duarte, 2011). The photosynthates from a fully expanded leaf can supply equivalent of 1500 g of fruit content of “Solo” varieties. The retaining of only 15 fully expanded leaves after a year of leaf pruning did not significantly affect fruit quality (total soluble solids), yield components (fruit size and quantity), and marketable yield. Usually, large fruited trees (4–5 kg each) may have fewer developing fruits for each duration on the fruit column, due to the physiological balance through fruit abortion and abscission of new flowers (Paull and Duarte, 2011).

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FIGURE 9.2 Soil moisture changes as observed under papaya in crop mixtures with okra and cucumber vegetables (H = Homestead selection, S = Sunrise solo).

9.15

INTERCROPPING AND INTER-CULTURE

Papaya is seldom grown alone in tropical plantations, but has often been grown mixed with other crops; as a component crop in mixed cropping systems or component of homestead gardens in backyard plantations and sometimes as a volunteer protected crop nurtured in association with other staple crops (Singh, 2003; Olubode, 2010a). Polyculture is a cropping system that imitates the diversity of natural ecosystems by accommodating multiple crops in the same area of land, as opposed to monoculture that comprised of large crop stands of same species (Neto et al., 2012). Although it is often labor intensive, few among the numerous advantages over monoculture is that polyculture is often more productive (Altieri et al., 1983; Vandermeer, 1990), provides an all year round availability of food security in the form of balanced diet (Vandermeer, 1990), provides resource use efficiency in

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optimum utilization of water and soil nutrient (Altieri et al., 1983; Vander­ meer, 1990), provides efficiency in adequate utilization of photosyntheti­ cally active radiation (PAR) (Altieri et al., 1983), provides better resistance to pests, epidemics, and weeds (Altieri et al., 1983; Hauggaard-Nielsen et al., 2001), assists in weed suppression in fruits orchard (Usoroh, 1989), contributes to livelihood, more economic returns, and yield stability, while the variability of crops provides habitat for more species, thereby increasing local biodiversity (Geno and Geno, 2001). This results in diversity of local diet and income, stability of production systems, reduced insect pest, and disease incidences, a more efficient use of labor, production is intensified with limited resources, and also available maximum returns under the low levels form of technology (Anil et al., 1998; Malézieux et al., 2009). Intercropping papaya with annual short duration vegetables at the juve­ nile papaya stages assisted in efficient land utilization as well as improved crop productivity (Olubode et al., 2008). The appropriate time to introduce component crops has been investigated. The late introduction of okra into papaya orchard was injurious to Homestead selection but not to Sunrise Solo due to component crops competition at the critical stage of the papaya physiological transformation from vegetative to reproductive (flowering/ fruiting) phase. This indicated that the early introduction of okra before papaya or simultaneous planting period could be regarded as the safe period to sow okra seeds into papaya orchards (Olubode et al., 2012a). Crop species’ interaction with papaya was varied in their responses and the ameliorative effect of the microclimate (Figs. 9.1 and 9.2). The lower crop performances of papaya planted sole compared to when crop mixed with cucumber showed an ameliorative effect of cucumber presence. However, introducing cucumber into papaya orchard at the critical growth period for both component crops caused significant growth retardation for both component crops. Lower profit margins were obtained from one intercrop­ ping cycle compared to papaya in sole cultivation which was eliminated by the higher cucumber yield at both the early and simultaneous intro­ duction periods (Olubode et al., 2011, 2012b). The competitive effect of component crops was reflected in retardation caused to both the vegetative and reproductive growth responses of Sunrise Solo, okra, and cucumber component crops compared with the individual monocrops (Olubode et al., 2012b). The introduction of vegetables before papaya or planting both simultaneously exhibited a form of stress situation resulting in significantly enhanced flowering of papaya (P ≤ 0.05) compared with late intercrop­ ping. Nonetheless, higher fruit yield of papaya was observed with late

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intercropping (42.7 t/ha) than with simultaneous and early intercropping (41.7 and 40.5 t/ha, respectively) (Olubode et al., 2012b). All papaya cropping systems were more advantageous than the monocrop of papaya and recorded higher productivity with land equivalent ratio (LER) of 3.86, 3.13, 2.06, 1.86, 1.60, and 1.54 in the crop mixtures with okra, watermelon, sweet potato, bush greens, Jews’ mallow, and scarlet eggplant, respectively (Aiyelaagbe and Jolaoso, 1992). Despite the effect suppression of weeds in papaya plots, both sweet potato and scarlet eggplant had marked retardation to papaya fruit yield. Furthermore, introduction of pumpkin (Curcubita maxima) into “Sunrise Solo” plots effectively suppressed spear grass (Imperata cylindrica) weediness which was comparable with hoe weeding or herbide spray using DelsateTM (Akinyemi et al., 2006). Intercropping with pumpkin has been reported to conserve soil moisture, caused increased earthworm activity and decreased diurnal maximum temperature (Olasantan, 2007). Notwithstanding the papaya infestation with mosaic virus when intercropped with chilli and brinjal, at the juvenile papaya stage more farmers in the cropping system practised papaya intercropped with chilli followed by papaya with brinjal, after which the papaya plants were used as poles to raise bottle gourd (Sarkar et al., 2010). A weed-free papaya field is achieved by light manual ring weeding at 30-cm radius around trees ensuring not to tamper with shallow rooting or by the use of herbicide. Earthing up may be done before or during rainy season to help the plants stand erect, to provide support and prevent logging of trees during rains. Staking of plants is done imme­ diately at the onset of flowering to prevent trees from lodging due to effect of overbearing fruits. Wind breaks are also required for shelter against damage by wind. Nonetheless, many cultural practices assist in maintaining low weed rating in papaya field such as intercropping with compatible short duration annuals, or with the use of organic manures or cover crops. During a four-month duration, preemergence herbicide of Alachlorin or Butachlorine (2.0g/ha) at two months after transplanting effectively suppressed weeds. Although weed biomass rating (WBR) was not different under papaya varieties, nonetheless wider canopy of unfertilized Homestead papaya had greater suppression on weed growth compared to unfertilized Sunrise plots. Moreover, higher WBR was observed in Sunrise sole but lower in Sunrise mixture compared to Homestead (Olubode et al., 2014a).

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9.16

Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

FLOWERING AND FRUIT SET

The papaya vegetative growth is described by a brief juvenile phase span­ ning a period of 3–6 months which terminates with the emergence of an inflorescence in the leaf axil, and a subsequent flower and fruit development (Plate 9.7) provided adequate climatic and cultural factors that are available. Poor environmental condition has an adverse effect on flowering and fruiting, such as carpelloidy, sex reversal occurrences, retarded pollen viability, and low sugar content of the fruit at temperatures below 20°C. At the occurrence of temperature falling below 12–14°C for several hours, particularly in dioe­ cious cultivars the growth and production are severely retarded (Nakasone and Paull, 1998).

PLATE 9.7 Papaya trees showing the female flowers, fruit set, and young fruits.

Flowering in fruit trees comprised of four stages of flower induction, flower initiation, flower differentiation, and blooming is an important repro­ ductive phenomenon that signals the commencement of fruit production (Ravishankar et al., 2014). Depending on the variety and climate condition, variations occur with the initiation of the flower primordial, the duration between seed germination and the first ripe fruit. Good nutrition assists in the process of flower initiation. Nitrogen especially has been shown to promote flower bud initiation in papaya and other fruits. Excessive nitrogen affects almost all plants by promoting and prolonging excessive vegetative growth and increasing shading which will have a negative effect on flower and fruit. However, nitrogen does not suppress flowering and fruiting in papaya (Rice

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et al., 1987). High temperature and low light intensity have a particular depressing effect on flowering, thus stimulating vegetative growth (Rice et al., 1987). The flower biology shows differences in flower whorls of dioecious and hermaphroditic plants. In hermaphrodite trees, pollination by wind is reduced to minimal since stamens are contained inside the corolla tube and rarely emerge out of the flower. The cleistogamous nature of hermaphrodite flowers (i.e., the anthers open and release the pollen ahead to floral anthesis) leads to self-pollination. Varieties from solo group are mostly self-pollinators, and such seeds more often than not breed true to type. Self-incompatibility is relatively rare, except for cases requiring controlled self-pollination, although self-pollination in papaya does not result in loss of vigor (Aquilizan, 1987; Paull and Duarte, 2011). The floral primordia of Solo is laid down 50–70 days before anthesis, where one flower in each leaf is formed every 2–3 days. Likewise, ovaries and stamen differentiation begin 42–50 days before anthesis (d.b.a.) and 50–56 (d.b.a.), respectively, and the two processes are concluded 28 and 35 d.b.a., respectively. Female flower bud emergence ranges from approx. 46 d.b.a. in Hawaii to 80 days before anthesis in India, with the wide variance is credited to temperature differences (Paull and Duarte, 2011). Male plants do not produce fruits but are required for cross-pollination at the rate of about one male plant to ten female plants (the cross-pollination is facilitated by insects and, to a lesser extent, by wind and birds) (Purseglove, 1974; Vandenabeele, 2014). Flowering commences during year one, and thereafter becomes year-round activity depending on climatic conditions. Male flowers as inflorescence are attached on long, flower stalks, while female flowers are larger with shorter stalks (Vandenabeele, 2014). In mixed stands of dioecious trees having both male and bisexual plants or in purely hermaphroditic stands, the pollination problem does not occur. Problems arise when for insufficient pollinizers dioecious cultivars are planted with fewer male trees. Usually, dioecious cultivars are planted at the recommended 8:1 or 10:1 female:male ratio. However, one male tree per 15–20 female trees is adequate in wind pollination fields if male trees are located in the direction of prevailing winds. Although auxins have been reported to induce parthenocarpy in papaya fruit, and occurrence of seedlessness and low seed count sometimes is observed on female trees, naturally parthenocarpy in papaya is rare. These seedless fruits are generally smaller in size (Paull

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Tropical and Subtropical Fruit Crops: Production, Processing, and Marketing

and Duarte, 2011). The rate of fruit set is in a direct relationship with that of fruit production and marketable fruit yield (Bodunde, 1999). Stamen deformities are frequent in areas of cool temperatures, the occurrence of which increases with decrease in temperatures in the computed average of 40 days before anthesis. The phenomenon occurs when the supposed 10 stamens arranged in a double whorl have only five stamens, while the remainder five get attached to the normal carpels. Severely distorted and unmarketable fruits result from the carpellody. Female sterility on the other hand occurs under warm temperatures, with tendency to occur at higher temperatures. Favor­ able conditions occurring under high nitrogen and moisture have influence on stamen deformities, while in reverse plant stress under N deficiency and moisture stress influences female sterility (Paull and Duarte, 2011). Studies on pollination by insects and wind give credence in favor of wind pollination as evidenced by the light nature of pollen and the high papaya pollen count (10–18% of total aero pollen) recorded at many loca­ tions (Chakraborty et al., 2007). Although maximum viability is observed on the day of anthesis, the pollen remains viable for 2 days before and after anthesis, and remains viable for 48 hrs at room temperature and 50% rela­ tive humidity. Fruit set is at maximum occurrence on the day of anthesis indicated by stigma receptivity of female and hermaphrodite flowers and remains for two days before and after anthesis. Pollination studies indicated that pistillate × staminate flowers result in 1:1 male:female progeny; pistillate × bisexual flowers result in 1:1 female:bisexual progeny; bisexual × bisexual flowers give 1:2 female:bisexual; while bisexual × staminate flowers give 1:1:1 female:male:bisexual progeny. The maximum number of fruit-bearing plants occurs with the second and third combinations (Malo and Campbell, 2001). 9.17 FRUIT GROWTH, DEVELOPMENT, AND RIPENING Fruits are matured and ready for harvest at 5–6 months after flowering at approx. 8–10 months following seed germination (Chay-Prove et al., 2000). Fruits are matured at 90 days after pollination and ripen within 2 or 3 days. The green color of mature fruit at ripening changes to yellowish green, and the white color of seed also changes to brown or black (Dinesh et al., 2017). Ripening, a senescence process leading to breakdown of cellular integrity

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of tissue, involves biochemical and physiological processes that comprised of changes in color, firmness, flavor, and aroma during the developmental or transitional phase. These processes occur during the last phase of fruit maturity till earliest phase of senescence of harvested fruits (Saltveit, 1999; Kader, 2002; Wills et al., 2007; Lin et al., 2009). Ripening in papaya is accompanied by an increase in many enzymatic activities of RNA, DNA, protein, and mitochondrial protein contents (Pal and Selvaraj, 1987). There are destructive indices and nondestructive indices used to determine papaya harvest maturity. The nondestructive indices include days from flowering, fruit size and external appearance (color), firmness, or texture, while the destructive indices include pH, internal pulp color %, and sugar content or total soluble solids (TSS—°Brix). 9.17.1

FRUIT DEVELOPMENT

The fruit growth and development occurs as a product of cellular activi­ ties that include cell division, cell enlargement, and/or both. Generally, the process of cell division is initiated following blossoming, but overlaps the cell enlargement activities, and continues until fruit maturity. Crop load shedding is done to improve fruit quality and to remove distorted fruits (Koller et al., 2016). Temperature has significant influence on fruit growth and development and the effect is more pronounced in subtropical areas. Optimum temperature requirement for growth ranges from 21 to 33°C; however below 12–14°C at night, significant negative influence affects growth and production (Paull and Duarte, 2011). Production of fruits during cooler season results in fruits of poorer quality due to retarded total soluble solids and smaller fruit size (Nakasone and Paull, 1998; Paull and Duarte, 2011). Fruit development from fruit set to ripeness ranges from 173 days under a 30°C day/20°C night (warmer condition) to 282 days at 24°C day/12°C night (cooler condition) (Allan et al., 1987; Olubode, 2010a). The growth curve varies for the month of fruit set and cultivar where the weight and length displayed double sigmoid type (Selvaraj et al., 1982a, 1982b; Ghanta et al., 1994), while a sigmoid curve is observed for fruit volume. A similar pattern for volume as occurs in fruit length was observed in warmer weather (Olubode, 2010a). There is, however, a positive correla­ tion observed between the number of seeds produced and the fruit weight (Olubode, 2010a).

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9.17.2

MATURITY INDICES

Among processes that occur during development and maturation of the fruit are those classified as desirable and undesirable changes. The common changes to expect include those that contribute to color change, flavor, resis­ tance to microbial and pest attack, human nutrition, and health. Contributing to these changes are the different classes of pigments (chlorophylls, carot­ enoids, flavonoids, betalaines) (Młodzińska, 2009). Some of these desirable or undesirable changes continue after harvest. The desirable ones include loss of chlorophyll (green color), development of carotenoids (yellow and orange color) in fruits, while undesirable changes include those that result in tissue browning such as changes in anthocyanin and other phenolic compounds (Kader, 2002). Other changes include conversion of starch to sugar, and of both starch and sugar to carbon dioxide (CO2) and water through respira­ tion, softening of fruits caused by breakdown of pectin and polysaccharides, increase in susceptibility to mechanical injuries, changes in flavor quality, loss of vitamin content, especially ascorbic acid (vitamin C), transpiration, and water loss (Kader, 2002). Consumers’ preference for specific color, flavor, texture, and fruit size varies for location and cultivar. Inappropriate color may be suggestive of loss of freshness and lack of ripeness (Pathare et al., 2013). Fruit size that remains constant is an important quality index during sorting and grading. Sweet flavor and firmness in texture are also ranked high in quality assess­ ment. When dealing with a large-scale processing the destructive methods of quality determination such as pH and TSS (°Brix) would require advanced technology for precision in decision-making. The colorimeter is an important instrument in the determination of skin color, and changes in color patterns that have similar trend within each fruit category. Mostly unripe fruits show initial greenish color preceeding changes to yellowish color as ripening progresses. Ripening in papaya is observed with light longitudinal stripes on fruits which progressively change to yellowish green and can show up irrespective of location on the fruit skin. The papaya when ripe usually gives off a powerful fruity aroma which is a quality index that is becoming increas­ ingly important for European consumers. As normally observed in climacteric fruit harvested at mature green stage, the soluble sugars increasingly occur in papaya fruit while being still attached to mother plant, while during fruit ripening starch content gradually diminishes from ≈0.13% in unripe fruits to ≈0.06% in ripe fruits (Gomez et al., 2002). On the other hand, the immature fruit when harvested does

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not ripen well as it is low in TSS (°Brix) exhibited in the tasteless fruit (Thompson, 2003). The cultivar type and maturity stage at harvest affect the soluble solids content of papaya which during harvest time could be 5–19% (Paull et al., 1997). The matured papaya stored at 20°C ripens normally, but the rate diminished at lower temperature. The ripening process is faster when storage temperature is higher which also affects fruit ripening including fruit color changes (An and Paull, 1990; Nunes, 2008). Crops harvested at the proper maturity stage are convenient for handlers’ various operations and result in the best attainable produce quality, unlike produce harvested too early that fails to develop flavor and results in improper ripening. The harvesting of produce at too late a period may however develop fibrousness or become overripe. Changes in latex color from white to watery are another index used to detect maturity in papaya fruit (Paull et al., 1997). 9.17.3

RIPENING PROCESS

The essential reason behind using physiological behavior to classify fruits into climacteric or nonclimacteric groups is based on the postharvest biology and behaviors of the commodities. The climacteric fruits are those usually harvested mature green and can ripen normally after harvest, while the nonclimacteric fruits are those harvested only when fully ripe (Wu, 2010). Ripening is that process through which fruits develop their desirable flavor, color, and textural properties (Kitinoja and Kader, 2002). Climacteric fruits are known to ripen after harvest once they have attained physiological matu­ rity. The rate of ripening of climacteric fruit after harvest can be controlled using various approaches such as cold storage (Khan et al., 2015), external application of various shelf-life promoting compounds among which are 1-methylcyclopropene (1-MCP), polyamines (PA), 1-aminoethoxyvenylg­ lycine (AVG), nitric oxide (NO), and methyl jasmonate (MJ) (Fan et al., 1998; Rath et al., 2006; Mattoo and Handa, 2008; Khan and Singh, 2009; Zaharah and Singh, 2013). Notwithstanding, there is a limited value in the use of cold storage due to the sensitivity of many fruits to chilling-related injury, while with the exception of MJ, many fruits show uneven ripening following the application of these exogenous applied chemicals (Fan et al., 1998). The normal ripening process is observed in papaya fruits kept under storage conditions at 15°C for 14 days when the temperature is raised to 25°C (Nunes, 2008). Notwithstanding, papaya fruits exposed to pests and diseases control measures at high temperatures above 30°C have retardation effects on fruit quality (Nunes, 2008).

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9.17.4 ARTIFICIAL RIPENING A group of chemicals termed “generally recognized as safe” (GRAS) are those chemical compounds that possess low toxicity along with their anti­ microbial, antifungal, and insecticidal properties, and which have received increasing acceptance for use in the control package of postharvest fruit diseases (Senti, 1981). These, although under regulations worldwide, have been adopted with very few limitations for many industrial and agricultural applications. These GRAS compounds offer a significant contribution in postharvest technology. Among the widely used GRAS in the food industry include peracetic acid, K-sorb, sodium bicarbonate, and calcium salts for leavening, pH control, taste, and firmness development. They operated on a broad spectrum basis the antimicrobial activity with abilities to inhibit various forms of postharvest diseases. The papaya fruit treated with ethylene attains ripening faster and in a more uniform manner attains desired qualities of skin degreening, softening, and flesh color (Wickramasinghe, 2006). Among the ethylene-releasing compounds mostly used for postharvest fruit ripening is calcium carbide an ethylene-releasing inorganic compound that for health reason has been prohibited by law in several countries. Despite this the compound is continuously being employed for ripening of fruits such as mango, banana, and papaya due to the inability of regulatory authorities to distinguish between fruit ripened with ethylene and the one with calcium carbide. A new approach called metabolomics, which employs both GC–MS and LC– QTOF–MS techniques, has surfaced with encouraging performances in the ability to distinguish between fruit ripened with carbide and the one with ethylene (Singh, 2015b). The metabolome is a holistic quantitative set of low-molecular-weight compounds (