Genetic variability in physiological and agronomic traits of newly developed rice lines under well-watered and water-deficit conditions

Water scarcity is a critical environmental stress that profoundly constrains rice growth and productivity. Consequently, the development of drought-tolerant and high-yielding rice genotypes is of paramount importance to sustain rice production and safeguard global food security. This field-based study aimed to evaluate the physiological and agronomic performance of diverse advanced rice breeding lines to identify genotypes with high yield and drought tolerance. A set of 15 newly developed rice lines and three check cultivars were used to assess their physiological and agronomic responses under well-watered (WW) and water-deficit (WD) conditions over two consecutive growing seasons, 2022 and 2023. The results showed highly significant differences (p < 0.01) among irrigation regimes, genotypes, and their interactions for all studied traits. Under WD conditions, there was a substantial decrease in chlorophyll content, relative water content (RWC), plant height, grain yield (GY), and yield attributes. On the other hand, leaf rolling, proline content, antioxidant enzyme activities (catalase and peroxidase), and sterility percentage were significantly increased compared to WW conditions. The genotypes L8, Sakha-107, and IRAT-170 had the best performance for chlorophyll content, RWC, and stomatal conductance under WD conditions, respectively. Additionally, L5 and L11 recorded the highest GY under WD conditions. The principal component analysis combined with correlation matrix analysis emphasized that both physiological traits (chlorophyll content, RWC, proline accumulation, peroxidase activity, and catalase activity) and agronomic traits (number of panicles per plant and GY) can be considered as effective selection criteria to improve productivity in rice breeding programs under limited water conditions. Notably, genotypes L5 and L11 demonstrated superior GY performance under water-deficit conditions, representing the most valuable genetic materials for drought-prone environments. These elite genetic resources constitute promising germplasm for introgression into breeding programs to enhance rice's drought resilience and maintain productivity under water-limited conditions.