Abstract
Problem statement: Synthesis of new-gene combinations by genetic manipulation is one of the powerful tools in exploiting the commercial qualities of plants and animals. Hybrid performance is evaluated from extensive yield trials that are costly and time consuming. Approach: Four silkworm races belonging to two different voltine groups (two multivoltine races namely Pure Mysore and Nistari and two bivoltine races namely C108 and NB4D2) and the twelve regular and reciprocal hybrids derived from them were reared under standard laboratory condition analyzing six quantitative traits namely cocoon weight, shell weight, shell ratio, filament length, denier and renditta. The data of the pure races was analysed for the estimation of evaluation index to study the genetic divergence between the races, where as evaluation index, heterosis and overdominance effects were studied in twelve hybrid combinations. Results: Varied heterotic effects were observed for different traits for hybrid combination. Cocoon weight and shell weight has maximum heterosis over the mid parent in Pure Mysore × Nistari (27 and 42% respectively), whereas C108 × Nistari have shown maximum shell ratio (30%) among the hybrids. The maximum filament length for heterosis was observed in the Nistari × Pure Mysore. Heterosis for cocoon weight, shell weight, shell ratio, filament length, denier and renditta based on evaluation index confirmed the above results. Conclusion: The investigation indicates that optimum level of genetic divergence between parents is necessary to obtain heterosis in F1 generation.
Highlights
Synthesis of new-gene combinations by genetic manipulation is one of the powerful tools in exploiting the commercial qualities of plants and animals
The dendrogram produced on Unweighted Pair Group Method with Arithmetic means (UPGMA) and cluster analysis indicated that the two bivoltines C108 and NB4D2 formed into one cluster, where as, the two multivoltines Pure Mysore and Nistari formed into another separate cluster (Fig. 1)
It is concluded from present studies that cross C108 × Pure Mysore, NB4D2 × Nistari, C108 × Nistari, C108 × NB4D2 and Nistari ×C108 could be further evaluated for selecting high cocoon characters genotypes due to its highest heterotic value for important evaluation index
Summary
Synthesis of new-gene combinations by genetic manipulation is one of the powerful tools in exploiting the commercial qualities of plants and animals. Heterosis, expressed as the improvement in a character shown by a hybrid over their mid- or better parental value, is a vital measure of the genetic progress made in plant, animal and silkworm selection. Doddaswamy et al.[3] studied heterosis effect on economic traits of silkworm, Bombyx mori L. and reported that heterosis was a result of overdominance and proposed that linked favorable dominant gene contributed to heterosis. Das et al.[2] carried out a series of out-breed crosses to select a suitable F1 hybrid for better silk production. They observed that heterotic effects were significant for most of the quantitative characters. Kumaresan et al.[11] observed that heterotic effect for different traits for different hybrid combination in their experiment
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