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.
Silkworm, being a poikilothermic insect, its growth and development is affected by environmental factors especially, temperature. In tropical countries like India, it has considerable effect on silk production due to the prevailing of hot climatic conditions. Previous attempts to evolve silkworm breeds and hybrids tolerant to high temperature by traditional breeding methods have not yielded the desired results. Hence application of new strategies like marker assisted selection (MAS) could be the most effective strategy for developing a thermo-tolerant bivoltine silkworm for sustainable silk production in India. As a prelude, in this study it is aimed to identify simple sequence repeat (SSR) markers closely linked with thermotolerance in silkworm. To do so, 20 silkworm breeds were evaluated at high temperature (36?C) and based on pupation percentage, two multivoltines (Nistari and Cambodge) and two bivoltines (SK4C and BHR3) were identified as thermo-tolerant and one bivoltine (CSR2) was identified as the susceptible breed. These breeds were screened with 85 SSR markers drawn from different linkage groups and out of those, only 11 markers (12.9%) showed distinct polymorphism between thermo-tolerant and susceptible breeds. Further, bulked segregant analysis (BSA) was performed using 11 polymorphic SSR primers, by comparing the SSR profiles of the tolerant (Nistari) and susceptible (CSR2) parents, their F1 and F2 bulks. Nevertheless, only 5 markers generated clear differences in the amplified DNAs between the bulks corresponding to that of the parents suggesting that the DNA regions amplified by these SSR markers are closely linked to thermotolerance in B. mori. The results obtained through bulk segregant analysis was further confirmed by genotyping 5 linked SSR markers using 140 individual F2 progenies. Of these 5 markers, highest Spearman's rho correlation coefficient was shown by S0816 indicating a high degree of closeness between the genotypic and phenotype variations in F2 population. Furthermore, we have also attempted to locate the genes near to S0816 by in silico approach and upshot revealed 3 genes nearer to its sequence on the B. mori genome. The BGIBMGA005249 gene was found to be located nearest to S0816 at a distance of 14.8 Kb. But, further studies are required in this regard to derive a relationship between the thermotolerance and the functional role of identified genes nearer to the closest marker, so that the identified markers can be used to develop a thermo-tolerant silkworm breed through MAS.
The tropical climate prevailing in India adversely affects temperate bivoltine silkworm rearing and causes crop loss especially during summer. Identification of high temperature tolerant bivoltine breeds by screening for thermotolerance in the silkworm, Bombyx mori (Lepidoptera: Bombycidae) is an essential prerequisite for the development of thermotolerant bivoltine breeds / hybrids. Therefore, in this study, 20 silkworm breeds were reared at different temperatures (25 ± 1°C,32 ± 1°C, 34 ± 1°C and 36 ± 1°C) for 6 h every day from 3 rd d of 5 th instar to till spinning. Significant differences (p < 0.01) were found among all the rearing traits over temperature. Based on pupation percentage, SK4C and BHR3 were identified as thermotolerant bivoltine breeds. Hierarchical clustering analysis based on rearing traits at tested temperatures grouped 20 silkworm breeds in four clusters which included one cluster each of susceptible and tolerant, and two clusters of moderately tolerant silkworm breeds. This suggests that clustering based on rearing data at high temperatures by using Euclidean distance can be an effective approach in classifying the silkworm breeds on their thermotolerance capacity. The identified breeds would be used for development of thermo tolerant bivoltine silkworm breeds / hybrids.
Aim: To compare the remunerativeness of Mulberry, Tasar, Eri and Muga based sericulture enterprises. Methodology: An empirical analysis was undertaken to compare the economics of mulberry and non-mulberry cocoon production in India, utilizing the available data from Central Silk Board using descriptive statistics and suitable ratios. Results: The study indicated that returns per rupee of investment in Mulberry (1.66), Tasar (1.60), Eri (1.88) and Muga (2.07) were higher compared to agriculture crop enterprises (National Silk Policy-2020), besides being of short duration with frequent assured income at least for three to six times in a year. Interpretation: The Mulberry and Eri silkworm cocoon production is highly remunerative enterprise and attracts the youths, because of its domesticated nature, short duration and women friendly enterprise. Key words: Cocoon production, Economics, Eco-friendly, Mulberry, Sericulture enterprises, Vanya
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