Genetic control of grain yield and its related traits in bread wheat.

Genetic control of tiller number, grain number, grain weight, harvest index and grain yield in six generations, along with the biparentals, F3s, F2xparental progeny, and F2xF1 progeny were investigated in an intervarietal cross of bread wheat involving two highly competitive varieties, 'WL711' and 'HD 2009'. The performance of F1, B1, B2, F2, × p1, F2 × P2 and F2 × F1 progeny was midway between the parents involved with respect to all the evaluated characters. The biparental progeny excelled the mean performance of their corresponding F2 and F3 progeny in tiller number, seed weight and grain yield. The estimates of variance components obtained from the two models deployed were almost similar. Considerable additive genetic variance was observed for grains per spike, seed weight and grain yield while dominance variance was more pronounced for harvest index. The additive-dominance model was adequate for grains per spike and harvest index. Epistatic effects of additive × additive and additive × dominance type for tiller number and grain yield, and of additive × dominance type for seed weight were observed. The digenic epistatic model was inadequate for explaining the nature of gene action for tiller number, seed weight and grain yield. The studies indicated that non-allelic interactions should not be ignored in formulating wheat breeding programmes and that a biparental approach could be adopted as an extremely useful tool for enhancing genetic variability and the creation of transgressive segregants. The usefulness of breeding methodologies utilising a biparental approach is discussed.