Genetic analysis of yield and associated traits in bread wheat crosses under deficit irrigation conditions using generation mean analysis

Drought stress severely limits bread wheat ( Triticum aestivum L.) productivity in arid and semi-arid systems. We used generation-mean analysis on six populations derived from two contrasting crosses (Giza-171 × Var-16, Cross I; PL-10 × Var-18, Cross II) evaluated under both well-watered and water-deficit regimes. Significant genotypic variation was detected for flag leaf area, chlorophyll content, spike number, spike length, kernels per spike, 100-kernel weight, biological yield, and grain yield. Drought Sensitivity Index (DSI) analysis highlighted two different patterns of drought adaptation. In Cross I, the tolerant parent (P₁) appeared to transmit its resilience to subsequent generations. In contrast, Cross II (F₁) exhibited hybrid vigor and maintained consistency. Scaling tests and a six-parameter model indicated the involvement of both additive and non-additive (dominance and epistatic) gene actions, with their relative contributions being trait- and environment-dependent. Grain yield showed marked mid-parent heterosis under drought conditions (30.50% in Cross I and 33.07% in Cross II), accompanied by substantial inbreeding depression (up to 41.83% in Cross I), highlighting the relevance of non-additive effects. Heritability estimates indicated the presence of genetic variation for grain yield under both optimal and water-deficit conditions, with consistently high broad-sense and moderate narrow-sense heritability across both crosses. Cross I exhibited favorable additive and complementary epistatic effects under drought, suggesting that it may be amenable to recurrent selection, whereas the heterosis observed in Cross II warrants further evaluation under water-limited environments. These findings provide preliminary genetic indications that may help guide future assessments of pedigree-based and hybrid breeding approaches.