Growth, Antioxidant, and Physiological Responses Associated with Tuber Yield in Cassava Under Irrigation and Late-Season Drought Conditions in a Tropical Savanna Climate

In tropical savanna climates such as the Northeast of Thailand, cassava is cultivated year-round but frequently experiences drought during storage root development, reducing productivity. However, the physiological mechanisms linking drought responses to carbon allocation and yield in Thai cassava cultivars remain poorly understood. In this field study, two cassava genotypes, including RY72 and CMR35–91–63, were planted during the late hot season (May 2022) and grown under either continuous irrigation (control) or drought conditions imposed for 60 days from 6 to 8 months after planting (MAP) during the dry season (November 2022 to January 2023), with no irrigation. Following the drought treatment, the plants were rewatered and allowed to grow until harvest at 12MAP. Moderate drought had a greater impact on carbon allocation and biomass accumulation than on photosynthetic capacity. Both genotypes maintained photosystem II efficiency, and photosynthetic performance under drought while enhancing antioxidant enzymes activity, thereby limiting oxidative damage and enabling rapid recovery after rewatering. During drought, photoassimilates were preferentially translocated to tuber in RY72 but to above-ground organs in CMR35–91–63. Following rewatering, RY72 hadhigher net photosynthesis rate and maintained higher sink activity of the tubers resulting in higher tuber biomass and starch content at final harvest. Therefore, stable photosynthesis performance together with high sink activity of storage roots during drought and after recovery are important characters alleviating yield loss in cassava subjected to late-season drought.