Antioxidant Enzymatic Activity and Its Related Genes Expression in Cassava Leaves at Different Growth Stages Play Key Roles in Sustaining Yield and Drought Tolerance Under Moisture Stress

The objective of this study was to explore the physiological and molecular mechanisms of a drought-tolerant cultivar (Xinxuan048, XX048) and a drought-sensitive cultivar (Kasetsart 50, KU50) at four growth phases under drought stress. Treatments were composed of three drought stress levels, viz., keeping the soil moisture content as 55–60%, 35–40%, and 15–20% of field capacity last for 15 days, respectively. Results showed that cassava growth and yield were substantially decreased with increasing drought stress. Oxidative damage enhanced with the increasing drought stress in both cassava cultivars. Compared with KU50 cultivar, XX048 showed stronger activation of the antioxidant defense system at different growth stages. This resistance to oxidative stress in XX048 was the result of increased accumulation of ascorbic acid (AsA) content and higher peroxidase (POD) and catalase (CAT) activities under drought stress. Furthermore, RNA-Seq data revealed that six drought-induced differentially expressed genes associated with antioxidant defense were also observed. qRT-PCR analysis showed that the relative expression levels of these genes were higher in XX048 compared with KU50. Conclusively, the XX048 cultivar was more beneficial in terms of high yield and drought tolerance due to more AsA content and higher POD and CAT activities and genes expression at different growth stages under water stress compared with KU50 cultivar. These data could provide fundamental knowledge for improving the approaches of cassava cultivation and molecular breeding with drought-resistant features.