Morpho-physiological traits and yield quality for cassava genotypes planted under drought during canopy establishment

Growth analysis provides better insight into the adaptability of cassava genotypes grown under drought conditions during canopy establishment and full irrigation. This study is intended to determine the growth rate and starch yield of different cassava genotypes grown under irrigation and drought treatments during canopy establishment. The experiment was conducted in two growing seasons at Khon Kaen University, Thailand, from August 2021 to August 2022 (2021/2022) and from August 2022 to August 2023 (2022/2023) using six cassava genotypes. A 2 × 6 split-plot design with four replications was used. The main plots were full irrigation and drought conditions during canopy establishment (90 to 150 days after planting (DAP)), and the cassava genotypes were assigned as subplots. The results showed that drought treatment applied during 90 to 150 DAP reduced relative water content (RWC) in cassava leaves for both growing seasons, storage root growth rate (SRGR) in the 2021/2022 growing season, and stem growth rate (SGR) and crop growth rate (CGR) in the 2022/2023 growing season. Re-watering after a drought supported cassava's growth rate, resulting in desirable yield and biomass at final harvest. The Rayong 72 and CMR38-125-77 produced significantly higher storage root dry weight, harvest index (HI), and starch yield than the other tested genotypes. Growing under drought treatment, the best performance in storage root dry weight with statistical significance for both years was recorded for CMR38-125-77 (11.2 and 11.4 t ha^-1 for the 2021/2022 and 2022/2023 growing seasons, respectively), and this was associated with a high crop growth rate (CGR, 12.3 g m^-2 day^-1 for the 2021/2022 growing season) and relative growth rate (RGR, 1.11 × 10^-2 g g^-1 day^-1 for the 2022/2023 growing season) during 180 to 360 DAP. These favorable cassava genotypes should be utilized for future plant breeding programs and cultivation to achieve the desired productivity in the growing areas with drought during canopy establishment.