Abstract:
This study was conducted to investigate black sigatoka disease and drought stress responses of off• type plants derived from shoot-tip micropropagation of East African highland banana (Musa AAA East Africa) landrace Uganda. Results showed that the off-type plants were more (p<0.05) tolerant to black sigatoka disease with the infection index of 17 .5% compared to 30.1 and 22.8% of the micropropagation (Ml') derived phenotypically normal plants and Conventional Propagation (CP) derived plants with no tissue culture history in their ancestry, respectively. On the contrary, the off-type plants were more (p<0.05) vulnerable to water stress with leaf senescence of 87.7% at soil water deficit of 630 millibars. The leaf senescence of the 1v1.P and CP derived plants at the same soil moisture deficit was 79.5 and 66.7%, respectively. During this stress period each off-type plant produced one sucker, while the true-to-type plants were unable to do so. Leaf structural analysis revealed that the off-type plants had higher (p<0.05) stomatal density of 16.0 mm-2 of the upper leaf surface. Conversely, the MP and CP derived plants had each 12.3 and 11.0 stomata mm ? of the leaf upper surface. Similarly, the off-type plant leaves were more hydrophobic with higher (p<0.05) epicuticular waxiness of
684.6 μg cm ". The epicuticular wax content of the 1v1.P and CP derived plant leaves was as low as 646.2 and
647.7 μg cm ", respectively. The water stressed off-type plant leaves exhibited higher (p<0.05) membrane damage with ion leakage of 168.2 μS cm" compared to 139.7 and 136.8 μS cm" of the 1v1.P and CP derived plants. Moreover, the water stressed leaves of the off-type plants had enhanced total antioxidant activity of
5.17 M trolox equivalent per milligram proteins, whereas the total antioxidant activity of the MP and CP derived
plant leaves was as low as 3. 76 and 3.67 M trolox equivalent per milligram proteins, respectively.
