Molecular Marker Assisted Breeding and Development of Bidensovirus Resistant and Thermo Tolerant Silkworm (Bombyx mori) Hybrids Suitable for Tropical Climatic Conditions

Bombyx mori bidensovirus (BmBDV) causes “Flacherie” disease leading to significant economic loss to sericulture industry. Resistance to BmBDV is controlled by the recessive gene, nsd-2 (non-susceptible to DNV-2). Consequently, screening and development of silkworm breeds for BmBDV resistance by artificial inoculation may not work as the nsd-2 resistant allele is in heterozygous condition. Deletion in nsd-2 gene is associated with the BmBDV resistance and hence can be used as a molecular marker. Silkworm breeds with nsd-2 resistant allele in heterozygous condition can be identified and selectively bred through marker assisted breeding. In the present study, twenty productive bivoltine breeds popular among the breeders for development of hybrids for tropical climatic conditions of West Bengal & Northeast region of India were screened to detect the presence of nsd-2 resistant allele. Out of twenty breeds, ten revealed the presence of nsd-2 resistant allele in heterozygous condition. Among the breeds which carried the nsd-2 resistant allele, SK6 and SK7, popular parental silkworm breeds of ruling hybrid for Northeast India were made homozygous for the nsd-2 resistant allele through marker assisted selection and were observed to be resistant to BmBDV infection and designated as SK6R and SK7R. The improved breeds SK6R and SK7R were further crossed to develop hybrids and these hybrids were also resistant to BmBDV infection retaining all the economic traits. The SK6R and SK7R breeds and their hybrids can be utilized for commercial silkworm seed production. This study also demonstrates utility of molecular marker, nsd-2 as a complementary tool to develop breeds and hybrids resistant to BmBDV infection.