Identification of Heat-Tolerant Rice Genotypes through Phenotypic Selection and Multi-Trait Characterization for Genetic Diversity

Rice (Oryza sativa L.), a global staple crop, is sensitive to elevated temperatures, particularly during reproductive and grain-filling stages. With climate change projections forecasting significant rises in mean temperature, sustaining rice productivity under heat stress has become a critical challenge. The present study evaluated forty-nine rice genotypes, comprising released varieties and advanced breeding lines, under control and heat-stress conditions. Phenological, morpho-physiological, and yield-related traits, were assessed to identify tolerant genotypes. Results revealed substantial variability among genotypes for chlorophyll content, membrane stability, spikelet fertility, and grain yield under stress. Heat-tolerant checks N22 and Rasi, along with genotypes L 663, L 672, MTU 1239, and CL 448, maintained higher chlorophyll levels, superior membrane integrity, and stable yields. In contrast, genotypes such as Vandana, MTU 1166, and MTU 1001 were highly susceptible, exhibiting severe reductions in chlorophyll content, spikelet fertility, and grain yield. Overall, traits such as minimal chlorophyll degradation, higher membrane thermostability, sustained spikelet fertility, and stable grain yield were strongly associated with heat tolerance. These findings highlight promising donor genotypes and key physiological traits that can be exploited in breeding programs to develop climate-resilient rice cultivars.