Integrative Dissection of Gene Action and Selection Gain for Climate-Smart Bread Wheat Genotypes Under Normal and Drought-Stressed Conditions: A Step Toward Sustainable Wheat Production

Diallel mating schemes provide an effective means of estimating general combining ability (GCA) and specific combining ability (SCA) among candidate parents, offering a basis for selecting suitable wheat-breeding strategies under water-deficit conditions. Seeds representing ten genetically distinct bread wheat genotypes—seven introduced accessions together with three Egyptian cultivars (Giza-168, Sids-12, and Misr-1)—were obtained from the Nordic Genetic Resource Center (NordGen). During the 2022–2023 winter season, these genotypes served as parents in a 10 × 10 diallel mating system at the Experimental Farm, Faculty of Agriculture, Sohag University, crossed in every possible combination (excluding reciprocals). The resulting F1 hybrids and their parents were then evaluated under normal (N) and drought-stress (DS) conditions. For most physiological and agronomic traits, parents P3 (NGB10893), P6 (NGB6681), P7 (NGB8950), and P9 (Sids-12) proved to be the best general combiners. Most of these traits also showed positive gains in their F1 crosses, reflecting favorable specific combining ability. The parents identified above therefore appear highly promising for a drought-oriented breeding program and may carry particularly desirable genes. For plant height (PH), number of grains per spike (NGS), grain weight per spike (GWS), 1000-kernel weight (TKW), grain yield per plant (GYP), and biological yield per plant (BYP), the expected genetic gain as a percentage of the mean (GAM), estimated from the F1 results under a 5% selection intensity, pointed to a relatively limited environmental effect on the expression of these traits. Such traits are governed by additive gene effects, which makes them amenable to straightforward selection. The dominance degree [a] was also determined for the remaining agronomic traits and for grain output per plant. All traits studied showed over-dominance (a > 1), except for NGS, which was governed by partial dominant variance (a < 1). Based on these findings, the combination of early maturity with favorable agronomic performance appears to signal stress tolerance, pointing to a practical route toward developing a high-yielding, drought-tolerant wheat germplasm and thereby accelerating breeding progress for stress tolerance.