(Role of Combining Ability and Gene Action in the Genetic Improvement of Maize (Zea mays L.))

This study aimed to evaluate the role of combining ability and gene action in the genetic improvement of maize (Zea mays L.) under open field conditions in The Research Farm of Faculty of Agriculture, Sohag University, Egypt. Eight inbred lines were crossed in a half-diallel mating design to produce 28 single-cross hybrids, which were evaluated along with two check hybrids at two sowing dates during the 2022 and 2023 summer seasons. The experiments were arranged in a randomized complete block design with three replications. Significant and highly significant differences among parental lines and their F1 hybrids were detected for all studied traits. Both general and specific combining ability mean squares were highly significant, suggesting that both additive and non-additive gene actions were involved in the inheritance of yield and its related traits. However, the predominance of non-additive effects was observed for most traits, especially for grain yield per plant, while additive effects were more important for 100- grain weight. Parents P₁, P₄, and P₈ were identified as good general combiners for yield and yield components, whereas hybrids such as P₁×P₈, P₆×P₈, and P₁×P₂ exhibited superior specific combining ability effects. The results emphasize that heterosis breeding through single-cross hybridization can be an effective strategy to improve maize productivity and stability under varying sowing conditions in Upper Egypt.