Effect of two cycles of direct selection on early heading and correlated
response in yield components were studied in the F3 generations of a cross between
Gemmeiza 3 and Sids 1 cultivars. Significant genotypic variations among the F3
families were obtained for heading date and yield components. Estimates of genotypic
and phenotypic coefficients of variability showed the presence of sufficient variability
for direct selection for all studied traits. Estimates of broad sense heritability were
relatively high and ranged from 65.06% for grain yield per plant to 73.94% for number
of spikes per plant, indicating that the proportion of genetic effects were greater than
those of environment. Heading date revealed positive genotypic correlations with
number of spikes per plant (0.41) and grain yield per plant (0.39). Whereas, the
genotypic correlation between heading date and 1000- grain weight was negative (-
0.37). These finding indicates that selection for early heading may slightly decrease
number of spikes per plant and grain yield per plant. After two cycles of selection in
the F3 families, the genotypic and phenotypic coefficients of variability decreased
rapidly for all studied traits. Consequently, the values of broad sense heritability
reduced from 73.6% and 65.1% to 47.4% and 48.1% for heading date and grain yield
per plant, respectively. These results showed that two cycles of selection in the F3
generations exhausted the genetiC variation and further selection will not be effective.
The results of observed gain after two cycles of direct selection showed that days to
heading was reduced by 9.1 and 7.0 days from F3 bulk families and the earliest
parent, respectively. Direct selection for early heading was accompanied with a
slightly decrease of 2.5 and 3.4 gm. in grain yield per plant after two cycles of direct
selection compared to the F3 bulk families and the better parent, respectively.
Although the reduction after two cycles of selection in yield components, some early
families still had high grain yield over both F3 bulk families and better parent. The early
high yielding lines obtained from this study could be used in developing new wheat
varieties for cultivation in new reclaimed areas, in Upper Egypt, where the water
supply is limited.