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

Abstract

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 environmentdependent. 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 nonadditive 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.