Selection for Grain Yield in Bread Wheat (Triticum aestivum L.) Under Normal and Heat Stress Conditions

The objective of the present work is to study the efficiency of pedigree selection in improving grain yield under normal and late planting dates. Two cycles of selection were completed under each date on the F₃ and F₄-generations. The F₅ selected families under normal and late planting were evaluated under both conditions. The genotypic variance was slightly less than the phenotypic variance under both dates and generally decreased from the base population (F₃) to the F₅-generation. Broad sense heritability estimates for grain yield/plant under normal and heat stress conditions were 81.76 and 75.04% after two cycle's selection, respectively. The realized heritability under normal date was 49.47 and 70.98% compared to 40.90 and 53.92% under heat stress after C₁ and C₂ respectively. The average observed gain from selection under normal and late planting groups, evaluated under normal planting date showed significant difference in grain yield from the bulk sample by 13.08 and 3.36%, and from the better parent by 25.04 and 15.04%, respectively. Under late planting date, the observed gain showed significant difference (P<0.01) of 6.73 and 7.78%, from the bulk sample and 16.05 and 22.10% from the better parent, respectively. Selection for grain yield under normal planting date evaluated under both dates, increased sensitivity of the selected families, while selection at late planting date, decreased the sensitivity.