A half diallel cross among seven bread wheat genotypes (Parents) namely
R.C.B 143, R.C.B 70, R.C.B 122, Sakha 202, Sakha 206, Gemmeiza 7 and Sids1
were evaluated for yield and its components as well as some other agronomic
characters in the F1 and F2 generations. Genotypes mean squares were significant
for all studied characters. Mean squares for parents In Crosses as an indication for
heterosis were significant for all studied cheracters in the F1 and F2, except plant
height and 1000-kernel weight in F1 and spike length, 1000-kernel and grain yield in
F2. Both general and spacific combining ability (GCA and SCA), were significant for
all studid characters in the F1 and F2, except SCA for plant height in F1 and spike
length in F1 and F2. These results indicate the importance of both additive and
dominance genetic variance in the inheritance of most characters. Though most of
estimates of not GCAlSCA exceeded unty, most of then was not significant to show
the probablity of equal importance of both addition and non-addition gene action.
Moreover, the parents P4 (R.C.B 122) and P5 (R.C.B 70) were the best combiners for
grain yield in F1 and F2 but P6 (Gemmiza 7) in F1 only. Meanwhile, significant SCA
effects for grain yield were found In the crosses between (P1xP3), (P1xP7), (P2xP4),
(P2xP6), (P3xP4), (P4xP7), (P5xP6) an (P5xP7) in the F1 and (P1xP3), (P2xP3),
(P3xP7), (P4xP5), (P4xP6), and (P5xP7), in the F2. The additive variance effects
were significant for all studied characters except for 1000 kernel weight, grain yield
and total plant weight in the F1, being significant for most characters in the F2. Over
dominance effects of heterozygous loci were significant for most studied characters in
the F1 and F2. Values of (H2I4H1) analysis being less than 0.25 indicated
asymmetric distribution of positive and negative alleles among parents for all
characters in the F1 and F2. On the other hand, narrow sense heritability was low for
some characters, indicating the importance non-additive genetic effects.