The genetic system controlling yield and its contributing i.e., flag leaf area, days to heading, number of spikes/plant, number of grains/spike, 1000-grain weight and grain yield/plant for six local and bread wheat genotypes were studied, under three treatments of irrigations (1-six irrigates 2- four irrigates 3- two irrigates). The diallel cross among parental genotypes in all possible combinations, exculuding reciprocals was used. The studied genotypes were, Sakha 93, Giza 168, Sahel 1, Gemmeiza 7, Gemmeiza 9 and Sids 1. This investigation was carried out during 2005/2006 and 2006/2007 seasons at Tag El-Ezz Agricultural Research Station, Dakhlia Governorate. In the second season 2006/2007 the obtained F₁'s together with the six parents were evaluated in randomized complete block design with three replicates for each treatment of irrigation. The obtained results showed that, mean squares for types of gene action according to Jones Method (1956), additive genetic variance (a) was significant for all characters under various irrigation treatments. Whereas, the dominance genetic components (b) was significant for all characters except, number of spikes/plant for first treatment of irrigation (I₁). By using second degree statistic (Hayman, 1954) results indicated that, the dominance genetic variance accounted for days to heading, number of spikes/plant (I₁, I₂ and I₃), number of grains/spike (I₁) and grain yield/plant (I₁ and I₂) resulting in (H₁/D)^0.5 which was more than unity. Both positive and negative alleles (H₂/4H₁) were not equally distributed among parents for all characters, except number of spikes/plant (I₁). Heritability in narrow sense was more than 50% for flag leaf area and days to heading (I₁, I₂ and I₃) as well as number of spikes/plant (I₃). The  mean squares of general and specific combining ability were significant for all characters. The wheat cultivars, Gemmeiza 7 and Gemmeiza 9 proved to be good general combiners. Wheat crosses; Sakha 93 X Gemmeiza 9, and Gemmeiza 7 X Sids 1 could be considered promising crosses and the best crosses combinations displayed for amount of heterotic effects for grain yield/plant.