Addis Ababa University Studies on the Economic Benefits and Extent of Drought Adaptation of Apple (Malus domestica Borkh.) Genotypes Introduced to Ethiopia By Abayneh Melke Woldegebriel A Dissertation Submitted to the Department of Plant Biology and Biodiversity Management in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biology (Plant Physiology) Addis Ababa University, Department of Plant Biology and Biodiversity Management Addis Ababa, Ethiopia January, 2019 ADDIS ABABA UNIVERSITY GRADUATE PROGRAMMES D E C L A R A T I O N This is to certify that the thesis prepared by Abayneh Melke Woldegebriel, entitled: Studies on the Economic Benefits and Extent of Drought Adaptation of Apple (Malus domestica Borkh.) Genotypes Introduced to Ethiopia; and submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in Biology complies with the regulations of the University and meets the accepted standards with respect to originality and quality and, the Thesis material has not been used in part or whole for any other qualification anywhere. II III ABSTRACT The present study was aimed at evaluating the economic benefits and adaptability of apple (Malus domestica Borkh.) genotypes domesticated, propagated, and cultivated in five different locations of Ethiopia’s highlands. In addition to in depth studies on the economic benefits of this useful fruit crop, the present thesis also focused on identifying early maturing, drought tolerant, as well as diseases and pest tolerant genotypes with desirable fruit yield and quality characteristics preferred by both the farmers and consumers. To this end, major apple genotypes introduced to Ethiopia during the last century were evaluated at five distinct geographical locations and under controlled glasshouse conditions. Eco-geographic characterization in five selected locations (namely: Holetta, Debrebirhan, Degem, Hidabu- abote and Agena) on eight apple genotypes (Anna, Dorsette golden, Princesa, Granny smith, Crispin, Gala, Golden delicious and Red delicious) identified specificity in the time of flowering, fruit setting and maturity, as well as adaptability of genotypes to the environments with respect to their chilling requirements for flowering and fruit setting. Results from field study conducted at these locations revealed that cultivar evaluation and selection will depend on growers’ preferred attributes such as maturity status of the genotypes (early, medium or late), fruit yield per tree, fruit weight, size and color, the type of rootstock used and branching habit of the scion. The present thesis found that genotypes Anna, Dorsette golden and Princesa consistently showed early maturity and high fruit yields at all the tested sites. Field studies conducted at Debrebirhan addressed physiological response of the eight genotypes to drought stress, by considering different physiological traits, including plant water relations (RWC), leaf water potential (ψw), net photosynthesis (Pn), stomatal conductance (Gs), transpiration rate (E), as well as water use efficiency (WUE). Total chlorophyll (Chl) content; growth performaces such as root dry mass (RDM), total biomass (BM), total leaf area (TLA), specific leaf area (SLA) and leaf area ratio (LAR) were determined and compared among the studied genotypes. Highly strong positive relationships were obtain between biomass and water use efficiency (r2 = 0.92); and between biomass and root dry mass (r2 =0.70). Drought susceptibility index identified that Anna, Dorsette golden and Granny smith were drought tolerant genotypes. Throughout the study period, these genotypes maintained higher RWC, ψw, WUE, Pn, RDM and low rate of Gs and E, compared to Golden delicious, Red delicious and Royal gala. IV Conversely, genotypes Golden delicious, Red delicious and Royal gala showed higher rates of Gs and E, hence their classification as drought susceptible genotypes. The aforementioned genotypes were also evaluated for drought tolerance in a glasshouse to further characterize their adaptability for drought prone areas. In addition to repeating measurements on the physiological parameters considered for the field studies, biochemical determinations on chlorophylls ‘a’ and ‘b’, proline, soluble sugar, lipid peroxidation expressed as malondialdehyde (MDA) content, drought induced soluble proteins (dehydrins) and antioxidant enzyme (AOX) activities, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX) were measured in leaves of apple genotypes maintained in a glasshouse and subjected to induced soil water potential (Ψmd) of ~ −2.75 MPa). Induced drought stress resulted in reduced RWC, leaf water potential (LWP), Gs, E and Pn in all the genotypes studied. Under drought stress, apple genotypes Anna, Dorsette golden and Granny smith maintained higher RWC, higher LWP and lower SLA, compared to Golden delicious, Red delicious and Royal gala. Clearly, the glasshouse studies confirmed the field studies that the former group of genotypes (Anna, Dorsette golden and Granny smith) are considered as drought tolerant, compared to Golden delicious, Red delicious and Royal gala. The overall results from the glasshouse and field experiments showed that plant water relations (RWC, LWP) and gas exchange measurements (Gs, E and Pn) appeared as a greater index of genotype’s tolerance or susceptibility to drought stress, followed by the elevated activities of antioxidant enzymes. Key words/Phrases: Apple phenology, tropical highlands, drought stress, drought susceptibility index, biomass, water use efficiency, leaf gas exchange, proline, V ACKNOWLEDGEMENTS I am greatly indebted to numerous people who contributed to the successful completion of this gallant piece of work. Special thanks go to my redemtive advisor Professor Legesse Negash for all the guidance and direction, invaluable comments, enthusiasm and encouragement. Dear Professor Legesse, your academic and social pieces of advice were very instrumental throughout the journey. Your kind support in all the activities done, friendly approach, and reflections with appropriate decisions deserve worth mentioning. Memories of our togetherness will linger in my mind forever as I advance my research career in Ethiopia or elsewhere for the benefit of farmers. I deeply acknowledge Dr. Bikilla Workneh, Head, Department of Plant Biology and Biodiversity Management, for the administrative support provided to finalize my study. My academic career would have been hardly possible without the continual support offered by the department. I am also greatly thankful to the National Biotechnology Research Institute hosted by Ethiopian Institute of Agricultural Research (EIAR) for providing me with full laboratory and glasshouse facilities which are unforgettable and very kind help that this work has come into fruitition. Special thanks go to Debremarkos University for providing me this scholarship. I recognize the role played by Woreda agriculture office managers and technical officers working on temperate fruits development program at Holetta, Debrebirhan, Degem, Hidabu – Abote and Agena/Ezha, (central and south central Ethiopia) for rigorously implementing the field trials. I wish to sincerely and greatly thank to apple growing communities for their cooperation in the entire research process period. I also recognize the Faji commercial apple farm PLC. (Faji Horticulture and Related Product Development Farm) at Debrebirhan and the farm owner, Mr. Abiy Astatkie for providing me with experimental site for field trial and facilitating the establishment and maintenance of the experimental plants until the completion of the study. Friends, your presence played a key role in the successful completion of my research work. Also many thanks should also go to all my colleagues at Addis Ababa University, College of Natural Sciences, especially at the Department of Plant Biology and Biodiversity Management. I acknowledge the companionship of my wife W/ro Mastewal Aniley and our sons Lealem Abayneh and Biniam Abayneh for their affection and encouragement throughout the study period. Also, I would like to thank my parents, who brought me up and toiled hard to educate me while they themselves remained illiterate. Above all, I salute the Almighty God for guiding, keeping and protecting me throughout the study period. VI TABLE OF CONTENTS Page Declaration ………………………………………………………………………… II Names and signatures of the examining board …………………………………… III Abstract………………………………………………………………………………. IV Acknowledgements ……………………………………………………………… VI List of figures …………………………………………………………………… XII List of tables ……………………………………………………………………… XIII Acronyms …………………………………………………………………............ XIV Chapter 1: Background of the study……………………………….. 1 1.1. Introduction………………………………………………… 1 1.2. Apple (M.domestica Borkh.): taxonomic position, origin and distribution 3 1.3. Genetic diversity of apples ………………………………………………. 5 1.4. Production trends and some popular apple cultivars of the world ………. 6 1.5. Requisite production conditions ……………………………………….... 6 1.6. Pollination and fruit setting in apple………………………….......... 6 1.7. Drought stress in apple: Physiological and biochemical perspectives…… 8 1.7.1. Physiological consequence of drought stress …………………….... 8 1.7.2. Physiological responses to drought stress in apple ………………… 9 1.7.3. Physiological characterization of drought responses in apple ……... 10 1.7.4. Physiological parameters affected by drought stress……………….. 13 1.8.