Integrating Griffing and Hayman Approaches to Dissect Gene Action for Yield Traits in Bread Wheat Under Normal Irrigation and Water Stress Conditions.

The analysis of variance revealed highly significant differences among parents and their crosses for all studied traits. Griffing’s analysis revealed significant effects of both general combining ability (GCA) and specific combining ability (SCA), indicating the contribution of additive as well as non-additive genetic components. Hayman’s Wr-Vr regression further confirmed these findings, revealing that over-dominance was predominant for most yield-related traits. Plant height, spike length, number of spikes/plant, grain yield/plant, and 100-grain weight under water stress conditions, whereas additive gene effects were more pronounced under normal irrigation for some traits such as days to 50% heading, weight of spikes/plant and biological yield. Parents located near the origin on the Wr-Vr graph, as well as those exhibiting high GCA effects (notably P3 and P5), were identified as the most promising combiners for yield improvement and drought tolerance. The integration of Hayman's and Griffing's analyses provides robust evidence for designing efficient wheat breeding strategies that combine heterosis exploitation under water-stress conditions with additive-based selection under irrigation to achieve sustainable genetic gains. These findings provide useful guidelines for breeding programs aiming to combine drought tolerance with high productivity in bread wheat.