Assessment of gene action for grain yield and its attributes in bread wheat using three diallel sizes

'The results indicate high degree of genetic variability existed among parental wheat genotypes and their FI crosses for days to heading, flag leaf area, yield and its components and protein content The in two number of superior genotypes that could be exploited through phenotypic selection was increased with increasing diallel size. The most desirable wheat genotypes that exhibited high grain yield and all , the relevant characters were Sids 1 and Line 1 and their Fl crosses (Gemmeiza 7 x Sids 1 and Sids 1 x Line 1 at 4x4 diallel size); Giz 168 and Line 2 and their F1 crosses (Gemmeiza 9 x Line 2, Giza 168 x Line 2 and Line 2 x Line 3 at 5x5 diallel size) as well as Sids 4, Cham 4 and Cham 6 and their Fl crosses (Gemmeiza 10 x Sids 4, Sids 4 x address, Cham 6 and Sakha 8 x Cham 4 at 7X7 diallel size). Consequently the breeder could be utilized the appropriate diallel size for isolating new recombinants with high yielding ability. The additive and dominance genetic components and their derived parameters differed in magnitude from diallel size to another. In general, both additive and dominance genetic components were significant and involved in the inheritance of days to heading, yield and its components and protein content in most cases at 4x4, 5x5 and 7x7 diallel sizes. The dominance component was larger in its magnitude than the additive [(Hl/D). '5 was more than unity] for the abovementioned characters. Additive gene action was the prevailed type controlling flag leaf area at 4x4 and protein content at 7x7 diallel level, whereas dominance component was more important in controlling flag leaf area at 5x5 and 7x7 diallel sizes. The covariance of additive and dominance gene effects in the parents (F value) was positive and significant for days to heading at 7x7 diallel size; flag leaf area and grain protein content at 4x4 diallel size as well as number of grains /spike and 1000-grain weight at 5x5 diallel size..