Genetic diversity is critical to success in any crop breeding and it provides information about the quantum of genetic divergence and serves a platform for specific breeding objectives. It is one of the three forms of biodiversity recognized by the World Conservation Union (IUCN) as deserving conservation.
Silkworm Bombyx mori, an economically important insect, reported to be domesticated over 5000 years ago by human to meet his requirements.
Genetic diversity is a particular concern because greater genetic uniformity in silkworm can increase vulnerability to pests and diseases.
Hence, maintenance of genetic diversity is a fundamental component in long-term management strategies for genetic improvement of silkworm which is cultivated by millions of people around the worlds for its lusture silk.
In this paper genetic diversity studies carried out in silkworm using divergent methods (quantitative traits and biochemical and molecular markers) and present level of diversity and factors responsible for loss of diversity are discussed.
Three new Multi x Bi combinations M.Con.4 x (SK6 x SK7), M.Con.4 x NB4D2 and Nistari x (SK6 x SK7) were studied in five seasons i.e. during the period of 18 th June-12 th July, 30 th August-23 rd September, 3 rd November-2 nd December, 29 th January-2 nd March and 30 th March-25 th April with one control Nistari x NB4D2 considering nine reeling characteristics along with shell percent and cocoon yield per 100 disease free layings (DFLs) to establish the seasonal effect on all the parameters. Results reveal that all the characters performed well in November-December. Highest yield per 100 DFLs was recorded during November-December in all combinations showing >60 kg yield. Higher correlation of yield/100 DFLs with filament length, non-breakable filament length, denier, raw silk percent, reelability percent and recovery percent was recorded in all combinations of Multi x Bi considered in this study. Variability observed among four combinations indicates the effect of different temperature and humidity of different seasons on expression of different traits. The results indicate that there is significant relationship of raw silk percent with reelability percent, recovery percent and evenness. Reelability percent showed higher correlation with recovery percent. It was observed that neatness was positively correlated with evenness. The overall performance of the newly evolved combinations with regard to productivity and reeling characteristics is discussed emphasizing their utilization at commercial level.
Thirty five bivoltine breeds were acclimatized under controlled condition for three years during two seasons to evaluate their efficiency in Seri industry of tropical region. Out of thirty five ten breeds had been short listed based on ranking for individual trait. Three breeds out of those ten selected breeds viz. SK6, NB18 and B.Con.4 ranked top in respect of overall performance. The ten breeds based on average Evaluation Index value > 50 considering twelve economically important traits are the resource material for future course of breeding program in West Bengal.
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