T. M. Igyuve, M. S. Mohammed, M. L. Umar, M. M. Abdulmalik, J. Ali Anaerobiosis, heritability, hybrids, rice, vigour 101-112 9 (3) 2025 July 2025 Anaerobic germination (AG) tolerance is critical for enhancing seedling establishment in direct-seeded rice (DSR), especially in flood-prone lowland ecosystems. This study investigated the genetic basis of AG tolerance in rice hybrids for Nigerian lowland ecosystems. The study evaluated 125 F₁ rice hybrids derived from five cytoplasmic male sterile (CMS) lines and 25 restorer lines using a line × tester design under both anaerobic and non-stress conditions. Significant genetic variation was observed for key traits, including germination percentage, seedling vigour index, plant height and root length. Broad-sense heritability ranged from moderate to high (h²b = 0.33–0.84) across most of the traits measured, with negligible values for fresh and dry biomass weight. General combining ability (GCA) analysis identified IR93560B, IR93559B, IR75596B and the tester UPIA 3 as superior parents with significant positive effects across multiple germination stages. Specific combining ability (SCA) analysis revealed that hybrids IR93559B × IRRI 143 and IR75596B × IR98153-15-1-1-1-1-1-1 exhibited consistently high germination rate under anaerobic and control conditions (both 100%). Strong positive correlations were detected between germination percentage and SVI, and between plant height and root length, supports the use of these traits in the selection of hybrids. Principal component analysis showed PC1 accounted for 50% and PC2 for 15% of total phenotypic variance. The study reveals the potential of specific CMS-restorer combinations for developing AG-tolerant rice hybrids, thus providing valuable information for breeding programs targeting climate-resilient, direct-seeded rice systems in Nigeria and beyond.