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Mean squares due to
reciprocal effects were non-significant for tillers per plant, spike
length, spikelets per spike, yield per spike and seeds index
indicating the presence of reciprocal differences among the hybrids
studied. The preponderance of additive genetic variation for five
traits in F generation indicated that the parents involved in these
crosses may be selected out on the basis of their GCA. The importance
of additive and non-additive gene action for these quantitative
traits in hexaploid wheat has also been reported by Larik et al.
(1992) and Sharma and Singh (1986).
3. GCA effects of the parents
Estimates of GCA effects of the parents are shown in Table 6. It is
evident that parents Z.A.77 and T.J. 83 were good general combiners
for single plant yield and other yield components. 'Me parents Z.A.77
had significant GCA for all yield components and single plant yield.
T.J.83 displayed similar results except plant height. The parents
Mon's and Z.A.77 had significant effects for tallness and were good
general combiner for this trait, while parents Blue Silver showed the
highest GCA effects for dwarness and can be exploited for breeding
dwarf genotypes. Parent Vee's was good general combiner for spike
length and seeds per spike (Table
6). It was
observed that the significant GCA effects of the parents, Z.A.77 and
T.J.83 for single plant yield were associated with the significant
GCA effects for some of the yield components. Such positive
association of GCA effects for yield components with GCA effects for
single plant yield of spring wheat was also reported by Liu et al.
(1989). This suggests that assessment on GCA effects for yield
components has considerable importance in selecting parents for yield
improvement.
4. SCA effects of the crosses
Estimates of SCA effects of the crosses (Table
4) showed that
there were a good number of crosses having significant and positive
SCA effects for single plant yield. The crosses were P1
x
P2, P2 x
P4,
P4 x
P6,
P5 x
P6,
P2 x
P1, P3 x P1, P4 x
P1, P5
x P1, P4 x
P2 and
P5 x
P2. These
crosses showed also significant and positive SCA effects for some of
the yield components. Seeds per spike showed significant SCA effects
in 12 out of 30 crosses. There were differences among the arrays of
parents from SCA effects of the cross. When all the characters were
considered, the arrays of Mon's, Vee's and Z.A.77 had maximum number
of estimates of significant SCA effects.
The crosses with significant SCA effects indicate presence of
non-additive (dominance and epistasis) gene action in them. The
combining ability studies indicate the existence of both additive and
non-additive gene actions in the present material. Additive gene
action was more prominent for yield components, while non-additive
gene action was strong for single plant yield. Therefore, breeding
method should be designed to exploit both additive and non-additive
gene actions. Diallel selective mating of Jensen (1970) has suggested
usefulness of such situation. But the method involves many crosses
among diverse parents and intermating in F1 populations, which makes
it difficult for practical utilization. However, the crosses which
have shown significant SCA effects for single plant yield may be used
in the development of hybrid variety. Another possibility of these
crosses is that the non-additive genes of the crosses would give
wider transgressive segregation. Careful selection of the potential
transgressive segregants through family selection would be worth
while for yield improvement.
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