This investigation was carried out at the farm of El‘Gemmeiza Agricultural
Research Station. Agricultural Research Center. Egypt. during 20022003 and
200312004 seasons. Six parental lines of bread wheat were used in a half-diallel cross
to produce Fr. crosses. Combining ability. heterosis. type of gene action and
heritabilitywere estimated for days to heading. plant height. Spike length. number of
headed tillers/plant. number of kernelsfspike. tOOO-kernel weight and grain
yieldi'plant .Gn‘ffing. Mather and Jinks and Hayman methods were used to estimate
these parameters. Significant mean squares were obtained tor genotypes. parents.
crosses for all traits studied. Kaman-2 and Sakha 59 were at the top of the tested
parents in grain yield/plant. The two crosses( Sakha 69 x Sids 7) and (Sakha 69 x Giza
170) gave the highest values of grain yieldiplant. The mean squares due to general
combining ability (GCA) and specific combining ability (SCA) were significant, for all
traits studied which indicated the presence of both additive and non-additive types of
gene action including dominance. The ratios of GCNSCA were more than unity in all
traits which indicated that additive gene effects were more important than dominance in
the performance of these traits.
The estimates of heterosis for grain yieldlplant indicated that twelve out of fifteen
crosses exhibited positive and significant heterosis relatively to mid parents. while five
crosses out of fifteen crosses exhibited positive and significant heterosis relatively to
better parent. All H; (the component of variation due to the dominance portion
associated with gene distribution values were smaller than H1 (the dominance
component of variation) values for all the studied traits. indicating unequal allele
frequency. Values oi (HrlD) “ were higher than‘units for most traits indicating over
dominance However spike length exhibited (H«.!D)'9 was less than unity suggesting the
existence of partial dominance effect The values of H2l4Hr for all traits were less than
D 25 for all the studied traits. indicating unequal distribution of dominant and recessive
alleles among the parents. Narrow sense heritability was high for days to heading. spike
length. moderate for number of headed tillers. number of kernels spike and lOOO—kernel
weight and low for plant height and grain yieldiplant.