Effects of solar UV-B radiation exclusion on physiology, growth and yields of taro (Colocasia esculenta (L.)) at different altitudes in tropical environments of Southern Ethiopia

Plants are sessile by nature, they have to be able to cope with exposure to many biotic and abiotic stress factors, including solar UV-B radiation. The degree of stresses varies with geographic locations. The impact of solar UV radiation on growth, physiology and yield of taro (Colocasia esculenta (L.)) at different altitudes under tropical environments was evaluated in Southern Ethiopia at 1500 m, 1800 m and 2200 m a.s.l. The experiment was conducted under open field conditions, and was compared to the yield of taro under UV-B blocking plastic film at every location. Four taro cultivars (‘Black’, ‘Boloso-1’, ‘Purple’ and ‘White’) were used as planting materials. Each treatment was planted using RCB design with three replications. The result indicates that leaf number, shoot number, leaf area and leaf area index under UV-B exclusion were found to be higher at higher elevation than either lower or middle elevation for ‘Boloso-1’ and ‘Black’ cultivars. Exclusion of UV-B spectrum from solar radiation improved the number of leaves and the leaf area index, for two cultivars: ‘Black’ and ‘Boloso-1’. Blocking UV-B radiation also significantly enhanced stomata conductance, photosynthesis rate stomata opening area, stomata number and dry matter in ‘Boloso-1’, compared to other cultivars. However, physiologically ‘Purple’ cultivar did not respond to solar UV-B irradiation. Among all the cultivars, ‘Boloso-1’ was found to be a good candidate for maximum corm size, marketable and maximum total yield production in all test locations irrespective of solar UV-B irradiation. In conclusion, vegetative growth of taro cultivars responded better to altitudinal variation than variability of UV-B irradiation. Whereas, physiological parameters like stomata number, stomata opening area, stomata conductance and photosynthesis of different taro cultivars responded stronger to the level of UV-B irradiation than the altitude.