Genetic Diversity, Combining Ability, and Gene Action in Diverse Rice Genotypes Under Contrasting Irrigation Regimes

Water scarcity is a major environmental constraint limiting rice production, particularly as climate variability increases the frequency and severity of water deficits. Therefore, developing high-yielding and drought-tolerant genotypes is essential for sustaining rice productivity. Exploring genetic variability and combining ability among parental genotypes is crucial for accelerating the breeding of resilient genotypes. This study characterized the molecular variations of thirteen local and exotic rice parental genotypes and evaluated their combining ability, inheritance patterns, and responses to water deficit. SSR-based molecular profiling revealed noticeable genetic variation among the parental genotypes. The parents were utilized to generate 30 F1 hybrids through line × tester mating design. The parents and their crosses were evaluated under well-watered and water-deficit regimes. Water-deficit stress substantially shortened days to heading and reduced plant height and flag leaf area. It also decreased relative water content, chlorophyll content, yield components, and grain yield per plant. In contrast, leaf rolling increased under water deficit conditions. Line × tester analysis showed that the non-additive gene effects accounted for most of the genetic variation and predominantly governed the inheritance of grain yield and all evaluated traits under both irrigation regimes. L1 and L3 were favorable general combiners for earliness. L6 and L7 emerged as superior combiners for reducing plant height. L2 and L10 showed favorable general combining ability for grain yield and several yield-related traits under water deficit conditions. The crosses L5 × T1, L2 × T2, L7 × T2, L10 × T2, L3 × T3, and L5 × T3 exhibited desirable specific combining ability effects for improving grain yield under normal and water-deficit conditions. Among them, L10 × T2, L3 × T3, L2 × T2, and L5 × T3 had high grain yield coupled with favorable yield-based drought-tolerance indices. Grain yield under water deficit was positively associated with relative water content, chlorophyll content, number of panicles/plant, fertility percentage, and 1000-grain weight. The identified parents and crosses represent promising breeding materials for enhancing rice grain yield under water-limited conditions.