A half diallel set of F2 crosses involving five parents were used to
estimate the type and relative amount of genetic variance components for days W
heading, plant height (cm), number of productive tillers/plant, main spike length
(cm), number of spikelets/main spike, number of grains/main spike, 1000-kernel
weight (g) and grain yield/plant (g) of wheat. The data were genetically analysed
according to the procedure developed by Griffing (1956 b) method 2 model 1.
Significant differences aniong the genotypes were detected for all the
studied traits. The mean squares associated with general and specific combining
ability (GCA and SCA) were highly significant for all the studied traits. The
magnitudes of the ratios of GCA/SCA revealed that the additive and additive by
additive types of gene action were the more important expression for all traits
except main spike length, number of spikelets/inain spike and grain yield/plant.
For the exceptional traits, the magnitude of additive and non additive types of
gene action were similar.
Estimates of , effects revealed that the parental line (P3) seemed lo be
the best combiner for high grain yield. While, the parental line (P1) followed by
Giza 157 exhibited significant negative , effects for heading date. The highest
desirable SCA effects were obtained in the following crosses: (P1 x P2), (P1 x P3).
(P1 x P4), (P1 x P5), (P2 x P4) and (P3 x P5) for heading date and (P3 x P5). (P2 x
P.3), (P1 x P5) and (P1 x P2) for grain yield/plant.
For days to heading, the parental variety Giza 157 gave the earliest
genotype. While, the P2 x P5 gave the highest grain yield/plant, but without
significant superiority over those of P1 x P4 and P2 x P,. Also, these crosses
exhibited significant positive heterotic effects relative to mid- and better parent.