Genetical Studies of Yield and its Components in Durum Wheat Under Heat Stress

The present study was carried out at Assiut Agricultural Research Station during 2007/2008, 2008/2009, 2009/2010 seasons. Diallel cross without reciprocals among eight parents of durum wheat namely, Sohag 3 (P₁), line #1 (P₂), line# 2 (P₃), Bin- Sweef 1 (P₄), Bin- Sweef 5 (P₅), Karifla (P₆), Altar 84 (P₇) and Admor (P₈) were used to estimate heterosis, and general and specific combining ability under recommended and late planting dates. Mean squares showed that highly significant differences among genotypes, parents and crosses for all studied traits in the F₁'s and F₂ generations, except number of spike/plant under late planting date. Moreover, both general (GCA) and specific (SCA) combining abilities were highly significant for most studied traits  in the F₁'s and F₂ generations under both planting dates except grain yield/plant, biological and number of kernel/spike in the F₁'s under late planting date in the SCA .The estimates of heterosis for grain yield/plant indicated  that seven crosses out of 28 F₁'s hybrids significantly surpassed their better parent with percentage ranged from 8.798 (P₄×P₇) to 41.22% (P₁×P₆). These relatively high heterotic percentage along with the variability existed among all diallel set increase the chance of good  recombination's that can be isolated in the following generations particularly, when selfing in the following generations gives an essentially homozygous state and enhances the role of selected plants in reducing the effects of dominance. However, the additive gene effect was of great importance in the performance of the most studied trait i.e. No. of spikes/plant, grain yield/plant (g), biological yield/plant (g), number kernel/spike. Moreover, the parents P ₇ and P₄ were good combiners for four traits i.e. Number of spikes/plant, grain yield/plant (g), biological yield/plant (g), number kernel/spike while, P₂ was the best for only three traits i.e. days to heading, maturity and number kernel/spike date in the F₁'s and F₂ generations. Meanwhile, significant SCA effects for grain yield were found in four out of the 28 F₁'s crosses P₁×P_4, P₁×P₆, P₄×P₇ and P₆×P₈ giving positive values of SCA effects under normal planting date and one cross P₂× P₄  under late planting date. On the other view, F₂ populations, one crosses P₃× P₈ gave positive values of SCA effects .while in the F₁'sand  F₂ generations, only one cross; P₃×P₈ gave positive values of SCA effects for 100- kernel weight under both planting date.