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According to the data
presented in Table
2, low yielding
parent Buc's and Blue Silver combine well to exhibit better parent
heterosis, which indicated the preponderance of additive gene action.
The hybrids P1x P2 and P4 x
P1 are likely to produce high yielding progenies in early
generations due to better specific combining ability
(Table
4), this
indicates that yield per plant is the expression of additive and
dominant genes. This is confirmed by the findings of Lupton (1961),
who found that certain crosses with large standard deviation but low
mean yield displayed greater promise than those with high yield.
According to East (1936), hybrid vigour may also be due to
accumulation and fixation of favourable genes, the maximum number of
which is brought together in the F1 hybrids, but the
intensity of action of certain genes which manifest heterosis may be
very low as a result of inbreeding.
Heterosis for these yield components has an important relationship
with heterosis for grain yield. The crosses expressing significant
and positive heterosis for yield per plant had significant and
positive heterosis for some yield components. In F1
generation significant and positive heterosis, particularly for spike
length, spikelets per spike, seeds per spike, yield per spike and
seed index was most frequently associated with significant and
positive heterosis for yield per plant (Table
2). Similar
positive relationship between heterosis for yield per plant and
heterosis for yield components was reported by Larik et al. (1988,
1992).
When the heterosis for the crosses was compared with their SCA
effects, it was observed that both were positively related. The
crosses P1 x
P2, P2 x
P4,
P4 x
P6,
P5 x
P6,
P2 x
P1, P3 x P1, P4 x
P1 and
P5 x P1 had significant estimates of both SCA
effects and heterosis for yield per plant (Table
4). Significant
estimates of both heterosis and SCA effects suggest predominance of
non-additive gene action for yield per plant in these crosses.
Selection through conventional breeding methods would not be
effective in these crosses, alternatively development of hybrid
variety might be a good choice.
2. Combining ability
The analysis of variance for general combining ability (GCA),
specific combining ability (SCA), and reciprocal effects (RE) are
presented in Table
5. Both GCA and
SCA variances were highly (P<0.01) significant for plant height,
spike length, seeds per spike and single plant yield, whereas GCA was
only significant (P<0.05) for fertile tillers per plant. RE were
highly significant (P<0.0 1) for plant height, seeds per spike and
single plant yield. GCA variance contains additive and additive x
additive epistasis while SCA variance contains dominance and additive
x dominance, dominance x dominance epistasis (Griffing 1956; Baker
1978), so the significant estimates of GCA and SCA variances
suggest that both
additive and non-additive gene actions were involved in controlling
these characters in the present materials. The variance for GCA were
larger than those of SCA for all the traits, which suggest that the
major portion of genetic variability in the base population was
additive in nature. Higher estimates of non-additive genetic variance
were noticed only for seeds per spike (Table
5).
These results suggest that
the yield components were predominantly controlled by additive gene
action. But seeds per spike were mainly controlled by non-additive
gene action.
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