Studies On The Economic Benefits And Extent Of Drought Adaptation Of Apple (malus Domestica Borkh.) Genotypes Introduced To Ethiopia

The present study was aimed at evaluating the economic benefits and adaptability of applern(Malus domestica Borkh.) genotypes domesticated, propagated, and cultivated in fiverndifferent locations of Ethiopia’s highlands. In addition to in depth studies on the economicrnbenefits of this useful fruit crop, the present thesis also focused on identifying early maturing,rndrought tolerant, as well as diseases and pest tolerant genotypes with desirable fruit yieldrnand quality characteristics preferred by both the farmers and consumers. To this end, majorrnapple genotypes introduced to Ethiopia during the last century were evaluated at five distinctrngeographical locations and under controlled glasshouse conditions. Eco-geographicrncharacterization in five selected locations (namely: Holetta, Debrebirhan, Degem, Hidabuaboternand Agena) on eight apple genotypes (Anna, Dorsette golden, Princesa, Granny smith,rnCrispin, Gala, Golden delicious and Red delicious) identified specificity in the time ofrnflowering, fruit setting and maturity, as well as adaptability of genotypes to the environmentsrnwith respect to their chilling requirements for flowering and fruit setting. Results from fieldrnstudy conducted at these locations revealed that cultivar evaluation and selection will dependrnon growers’ preferred attributes such as maturity status of the genotypes (early, medium orrnlate), fruit yield per tree, fruit weight, size and color, the type of rootstock used andrnbranching habit of the scion. The present thesis found that genotypes Anna, Dorsette goldenrnand Princesa consistently showed early maturity and high fruit yields at all the tested sites.rnField studies conducted at Debrebirhan addressed physiological response of the eightrngenotypes to drought stress, by considering different physiological traits, including plantrnwater relations (RWC), leaf water potential (ψw), net photosynthesis (Pn), stomatalrnconductance (Gs), transpiration rate (E), as well as water use efficiency (WUE). Totalrnchlorophyll (Chl) content; growth performaces such as root dry mass (RDM), total biomassrn(BM), total leaf area (TLA), specific leaf area (SLA) and leaf area ratio (LAR) wererndetermined and compared among the studied genotypes. Highly strong positive relationshipsrnwere obtain between biomass and water use efficiency (r2 = 0.92); and between biomass andrnroot dry mass (r2 =0.70). Drought susceptibility index identified that Anna, Dorsette goldenrnand Granny smith were drought tolerant genotypes. Throughout the study period, theserngenotypes maintained higher RWC, ψw, WUE, Pn, RDM and low rate of Gs and E, comparedrnto Golden delicious, Red delicious and Royal gala.rnVrnConversely, genotypes Golden delicious, Red delicious and Royal gala showed higher ratesrnof Gs and E, hence their classification as drought susceptible genotypes. The aforementionedrngenotypes were also evaluated for drought tolerance in a glasshouse to further characterizerntheir adaptability for drought prone areas. In addition to repeating measurements on thernphysiological parameters considered for the field studies, biochemical determinations onrnchlorophylls ‘a’ and ‘b’, proline, soluble sugar, lipid peroxidation expressed asrnmalondialdehyde (MDA) content, drought induced soluble proteins (dehydrins) andrnantioxidant enzyme (AOX) activities, such as superoxide dismutase (SOD), catalase (CAT),rnascorbate peroxidase (APX) and glutathione peroxidase (GPX) were measured in leaves ofrnapple genotypes maintained in a glasshouse and subjected to induced soil water potentialrn(Ψmd) of ~ −2.75 MPa). Induced drought stress resulted in reduced RWC, leaf waterrnpotential (LWP), Gs, E and Pn in all the genotypes studied. Under drought stress, applerngenotypes Anna, Dorsette golden and Granny smith maintained higher RWC, higher LWPrnand lower SLA, compared to Golden delicious, Red delicious and Royal gala. Clearly, thernglasshouse studies confirmed the field studies that the former group of genotypes (Anna,rnDorsette golden and Granny smith) are considered as drought tolerant, compared to Goldenrndelicious, Red delicious and Royal gala. The overall results from the glasshouse and fieldrnexperiments showed that plant water relations (RWC, LWP) and gas exchange measurementsrn(Gs, E and Pn) appeared as a greater index of genotype’s tolerance or susceptibility torndrought stress, followed by the elevated activities of antioxidant enzymes.

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