STUDIES ON COMBINING ABILITY AND HETEROSIS IN SOME BIVOLTINE BREEDS OF SILKWORM, Bombyx mori L.
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Date
2009-08-18
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University of Agricultural Sciences GKVK, Bangalore
Abstract
Investigations were carried out to study the combining ability and heterosis in some
bivoltine silkworm breeds through Line x Tester analysis. Seventeen bivoltine pure breeds were
reared twice and evaluated for fifteen quantitative traits so as to finally select the parents. Based
on the multiple traits evaluation index values, seven oval cocoon breeds viz., SH-6, KPGA,
CC-1, CSR-2, CSR-27, KSO-1 and APS-5 were selected as lines and crossed with each of the
selected dumbbell cocoon breeds viz., NB4D2, CSR-4, CSR-26, APS-8 and NP-2. All the 35
single cross hybrids and their parents were evaluated across three seasons (rainy, winter and
summer) for fourteen quantitative traits. The mean performance among the hybrids was
significantly superior in KSO-1 x CSR-4 for eleven traits, followed by SH-6 x CSR-4, KSO-1 x
NB4D2, KSO-1 x NP-2, APS-5 x NP-2, APS-5 x CSR-26 and APS-5 x APS-8 for ten traits each.
The variance due to specific combining ability (SCA) was higher than that of the general
combining ability (GCA) for all the traits, indicating the predominance of non-additive gene
action in controlling the traits. The parents, KSO-1, APS-5, CSR-2 and CSR-27 as lines and
NP-2 and CSR-4 as testers were the best general combiners for most of the traits. KSO-1 x
CSR-4 ranked top by recording the highest specific combining ability for eleven traits. While,
KPGA x NB4D2 and CSR-2 x CSR-4, KPGA x APS-8 and APS-5 x CSR-26 hybrids yielded
high SCA effects for eight and seven traits each, respectively. Higher heterotic value for majority
of the traits was exhibited by KSO-1 x CSR-4, APS-5 x CSR-26, CSR-27 x CSR-4, APS-5 x
APS-8 and CSR-27 x CSR-26 hybrids. The multiple traits index value was highest in KSO-1 x
CSR-4 and it ranked top among hybrids. Considering the rearing performance, specific
combining ability, heterosis and evaluation index, KSO-1 x CSR-4 was adjudged as the potential
hybrid for commercial exploitation. Genetic divergence among the seventeen bivoltine breeds
indicated a distant diversity as they formed six clusters. The large-scale evaluation of KSO-1 x
CSR-4 hybrid at three different locations revealed its better performance over CSR-2 x CSR-4
and KPGA x NB4D2 hybrids.
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