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|Title: ||Genetic Divergence in Some Bivoltine Silkworm (Bombyx mori L.) Breeds.|
|Authors: ||Asma Maqbool, (Scholar)|
Dar, H. U. (Guide)
|Issue Date: ||2010|
|Abstract: ||Sericulture industry has been benefited tremendously through exploitation of heterosis. Silkworm hybrids in general, are superior to pure breeds in growth, vigour and economic traits. In order to improve yield and quality of silk, it is pertinent to characterize the potential of available allelic resources in transferring desirable performance to hybrid progenies. Selection of parents on the basis of per se performance does not always lead to fruitful results. The selection should be based on a thorough knowledge of genetic diversity of parents with regard to traits that need to be improved. More diverse the parents, greater are chances of obtaining higher amount of heterotic expression and also more variability is expected to appear in segregating generations of such crosses.
In the present study twenty eight bivoltine silkworm (Bombyx mori L.) genotypes were grouped into five clusters on the basis of Mahalanobis D2 analysis. The twelve genotypes selected from among these D2 clusters were again grouped into five groups on the basis of analysis of six isozymes viz., alkaline phosphatase, amylase, aspartate amino transferase, esterase, peroxidase and succinate dehydrogenase. The estimates of genotypic correlation coefficients were higher in magnitude than the corresponding estimates of phenotypic correlation coefficients. All the isozymes studied were found associated with yield parameters viz., single cocoon weight, single shell weight, cocoon yield/10,000 larvae by number and cocoon yield/10,000 larvae by weight. No genotype displayed a significant superior performance vis-à-vis check breeds in all the metric traits under study. However, several genotypes registered higher performance in several subsets of traits.
In view of the results obtained it could be conceived that the genetic distance and not the geographic diversity are to be considered while identifying parents for hybridization programme. The choice of characters is also important while planning the cross breeding programmes. Out of thirty three bands observed for six isozymic systems, twenty seven were polymorphic. Moreover, the enzymes showed an appreciable range of relative mobility and activity suggesting their usefulness as genetic markers for genotype identification. Based on the mean performance of genotypes and the genetic distances between them it can be conceived that the genotypes NB4D2, SH6, Meigitsu, CSR4, Sheiki II, Pampore-5, J122, J2M, 14M, JBEL, NJ3 and B38 could be used for hybridization programme in future. In the present study weight of mature larvae, single cocoon weight, single shell weight, cocoon yield/10,000 larvae by number and filament length exhibited a significant positive correlation with cocoon yield/ 10,000 larvae by weight. Hence these are the core characters determining economic end product (the yield). These traits also revealed strong genetic association with one another. Hence simultaneous selection of these traits would help in increasing the efficiency of selection while evolving high yielding genotypes or in the amelioration of deteriorated breeds. The enzymes studied, being associated with certain yield parameters can be utilized in marker assisted selection (MAS) programmes for the improvement of silkworm. In spring the breeds J2M, A and NCD displayed significantly superior performance in several subsets of traits while, genotypes CSGRC-5, New race, JA1 and Jam 21 surpassed the check breeds (NB4D2 and SH6) in a good number of metric traits during summer. The genotypes Sheiki II, Pampore-5, J122, Meigitsu, 14M, NJ3, NB18, CSR2 and CSR4 were significantly superior to the check breeds in several subsets of traits in both spring and summer. This information can be utilized for evolving new season specific breeds with accumulation of maximum desirable traits.|
|Appears in Collections:||Sericulture|
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