Abstract
Twenty-eight genotypes of bivoltine silkworm (Bombyx mori L.) were studied for genetic divergence using Mahalanobis D2 statistic. Based on fifteen important metric traits, D2 values were obtained and the genotypes were grouped into five clusters using Tocher’s method. The clustering pattern indicated a mixed trend. The silkworm genotypes originating/evolved from different geographical regions fell in the same cluster. The inter-cluster distance ranged from 6142.45 to 19605.60. The genetic divergence was maximum between Clusters 5 and 2 followed by that between Cluster 3 and 2. Fifth age larval duration (19.56%), Total larval duration (15.93%), weight of mature silk gland (16.73%), Single cocoon weight (11.29%), Cocoon yield/10,000 larvae by No. (22.78%) and Denier (13.11%) contributed maximum towards the total genetic divergence. The results reveal that while identifying parents for hybridization programme, genetic distances and not the geographic diversity are to be considered. The choice of characters is also important while planning the cross breeding programmes. Key words: Cluster, genetic divergence, heterosis, silkworm.
Highlights
In order to synthesize high yielding silkworm hybrids it is important to have a collection of varied gene pool of silkworm races, because variability is the basic requirement for the genetic improvement of any crop
Fifth age larval duration (19.56%), Total larval duration (15.93%), weight of mature silk gland (16.73%), Single cocoon weight (11.29%), Cocoon yield/10,000 larvae by No (22.78%) and Denier (13.11%) contributed maximum towards the total genetic divergence
To create new reservoirs of genetic variability cross breeding strategies have been extensively used as a means of harnessing heterosis in the bivoltine silkworms (Narayanswamy et al, 2002)
Summary
In order to synthesize high yielding silkworm hybrids it is important to have a collection of varied gene pool of silkworm races, because variability is the basic requirement for the genetic improvement of any crop. The silkworm genotypes originating/evolved from different geographical regions fell in the same cluster. Fifth age larval duration (19.56%), Total larval duration (15.93%), weight of mature silk gland (16.73%), Single cocoon weight (11.29%), Cocoon yield/10,000 larvae by No (22.78%) and Denier (13.11%) contributed maximum towards the total genetic divergence.
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