Genetic effects and combining ability for agronomic and yield traits clustered with biochemical profiling of rice (Oryza sativa L.) under optimal and water deficit conditions

In order to evaluate the combining ability and genetic effects for morpho-physiological and yield parameters in rice under well-watered and drought situations, this study was conducted in Sakha, Kafr El-Sheikh, Egypt, during the summers of 2023 and 2024. Seven rice accessions were intercrossed in a 7 × 7 half-diallel scheme, generating a total of 21 F₁ hybrids during summer 2023. In 2024, parents and F1 hybrids were evaluated in a RCBD under control watering (every 4 days) and water-deficit stress (every twelve days). Significant variations observed among the genotypes and their components revealed substantial genetic diversity. Hybrids; GZ 179 × IET-1444 and IET-1444 × HR-5824 exhibited the highest mean performance for most traits under both conditions. For every variable, ANOVA revealed highly significant G.C.A and S.C.A impacts. Additive effects dominated for earliness and 1000-grain weight, whereas non-additive effects controlled traits viz., chlorophyll content, yield/plant-1, and harvest index, indicating that effective selection and hybridization are crucial in rice adjustment. GZ 179, Sakha 107, and IET-1444 were the best general combiners, whereas GZ 179 × IET-1444, GZ 179 × HR-5824, and IET-1444 × HR-5824 were superior specific combinations at both environments. Under drought, antioxidant enzyme activities, proline, and phenolic contents increased, while Malondialdehyde (MDA) and R.O.S radical levels decreased, indicating enhanced stress tolerance. Cluster analysis grouped genotypes by drought response, identifying tolerant rice entries with strong biochemical defense and stable yield performance.