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Thus, it may be concluded
that the variance due to gca is by and large more important in a crop
like wheat. However, both gca and sea variances were highly
influenced by their interaction with environments. The sea variance
was more pronounced for grain yield than the other yield components.
Most of the sea was retained in the successive generations. This is
encouraging because it indicates the fixable nature of non-additive
gene effects. In a crop like wheat, this is important because
commercial hybrid production is not the objective. But the genie
interactions that would be fixable would lead to transgressive
segregation wherein some segregants would exceed the limits of their
parents.
A perusal of the general combining ability (gca) estimates
(Table
2)
showed the transcendency of the parents HD 2204 and Raj 1482 for
grain yield as good general combiners (on the basis of F2
analysis) while Brochis was a consistently low combiner for grain
yield. The two high combiners for grain yield also showed superior
high combining ability for some of the component traits. Parent HD
2204 was also a high combiner for earliness, dwarfness, number of
grains per spike, grain weight per spike and 1000 grain weight.
Similar results were shown by parent Raj 1482 but it was not a high
combiner for 1000 grain weight. It was an average combiner for grain
weight per spike and a low combiner for 1000 grain weight.
Apparently, therefore, there is still further scope for improving
upon the combining ability for component traits as none of the high
combiners for grain yield was a high combiner or at least an average
combiner for all the desirable traits. As compared to this, the
lowest combiner Brochis was average to low combiner for all the
component traits. Almost similar situation was shown by other low
combiners, namely, Pavon and Kharchia 65. Other parent Moncho was
high combiner only for spike length, number of spikelets per spike,
number of grains per spike; WL 711 for spike length; D65 for 1000
grain weight; Raj 821 for earliness, 1000 grain weight and parent
Chiroca for number of spikelets per spike, number of grains per spike
and grain weight per spike.
It seems feasible, therefore, that the gca rank for grain yield is
related to the gca for the useful yield components. It is, therefore,
recommended that breeders should breed for superior combining ability
for the component traits with an ultimate objective to improve the
overall gca for grain yield in wheat. The parents HD 2204 and Raj
1482 could be utilized extensively in hybridization programme to
accelerate the pace of genetic improvement of grain yield in bread
wheat.
The analysis of specific combining ability (sea) effects revealed
that nine crosses showed high sea on the basis of F1
analysis but in the F2 only three crosses seemed to show
high sea for grain yield. However, cross WL 711 x Chiroca showed the
highest sea effects for grain yield in both F1 and
F2 generations. This cross also exhibited maximum
heterosis of 89 per cent for grain yield. Apart from this cross,
however, there seems to be no correlation between the rank for sea
and the rank for heterosis. This could be expected, because heterosis
estimates are worked out from the mean values whereas the sea
estimates are related to the gca of parents. The most consistent
cross for high sea effects was Kharchia 65 x Chiroca which showed
high sea under all situations. Other best crosses for grain yield was
Brochis x Kharchia 65, Brochis x Raj 821 and Brochia x D 65. All the
best crosses for grain yield also showed average to high sea for most
of the yield components. It is, therefore, recommended that new
materials are used in future breeding programmes for recombining the
desirable traits in the envisaged elite genotypes.
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