Responses of east African highland banana (EAHB-AAA) cultivars to drought stress
Banana (Musa spp.) yields are estimated at 5-30 t ha-1yr-1, lower than the potential 60 t ha-1yr-1, with the cause being drought stress. Much evidence among stakeholders shows little understanding about banana cultivar sensitivity, escape and avoidance mechanisms to drought due to un-attempted measures of retaining plant growth during escalating dry spell. This study aimed at determining cultivar expression as a way of dealing with drought. Triploid cooking cultivars of Mpologoma and Kisansa (AAA) versus the considered drought tolerant cultivars of Kayinja (ABB), Sukali ndiizi (AAB) and a low land cultivar Yangambi Km5 (AAA) were grown under a semi-micro environment, with controlled soil evapo-transpiration. Cultivars were grown on three sandy loam soil water regimes under pF- curves of 10log matrix head of Wet: 2.0-2.1 (0.1 - 0.13 bar) equivalent to 90% moisture availability (M.A.); Semi-moist: 2.5-2.7 (0.32 - 0.51 bars) equivalent to 60% M.A. and Dry: 2.8-2.9 (0.64 - 0.8 bars) for 30% M.A., respectively. Results showed that an increase in soil moisture deficit from moist to dry condition caused a proportional loss in fresh biomass of up to 50% among cooking cultivars, and less than 40% to dessert cultivars. Leaf orientation was significant to folding with cooking variety type opening leaves widely (up to 100o), and enhancing excessive leaf plant dehydration, even during stressful conditions. Soil evapo-transpiration showed that cvs. Kisansa and Mpologoma transpired up to 1.125L 48 hr-1, exhibiting a trait for water spending than saving. Thus, cultivars comprising of genome (B) expressed crucial mechanisms of avoiding excessive effect of drought stress. Therefore, under high moisture deficits, Kayinja and Sukali ndiizi cultivars express drought avoidance mechanisms through leaf folding. But, the cooking type of cultivars Kisansa and Mpologoma (genome A), develop extensive rooting system important in search for moisture; and large leaf surface characterised by high rate of transpiration for water spending.
Key words: Musa spp., soil moisture, transpiration