Estimating combining ability is essential for evaluating genotypes and understanding the nature and magnitude of gene actions involved in plant breeding. In a study involving four lines and seven testers, a Line × Tester mating design was employed to analyze combining ability, heterosis, and gene action across 16 yield-related traits. The results indicated significant variances for general combining ability (GCA) and specific combining ability (SCA), underscoring the relevance of additive and non-additive genetic components in trait inheritance. The analysis revealed that the ratio of dominant genetic variance to additive genetic variance was greater than one for most traits, with the exceptions being test weight and the grain length:breadth ratio. This suggests that non-additive gene action predominantly influences the inheritance of the examined traits. Among the parental lines studied, CO 54, CO 55, RL 8601, RL 6298, and RL 27 emerged as the best general combiners for single-plant yield and other traits. Based on the outcomes of standard heterosis, the following hybrid combinations were identified as optimal for augmenting single-plant yield: ADT 58 × RL 2348 (105.33%), CO 55 × RL 6298 (104.5%), CO 54 × RL 6298 (103.87%), CO 54 × RL 8601 (100.76%), ADT 58 × RL 2196 (99.8%), and ADT 56 × RL 6298 (97.65%). These results indicate that the identified cross combinations could be effectively employed in recombination breeding programs focused on producing early-maturing, high-yielding fine-grain rice varieties that align with market requirements.
