DEVELOPMENT AND EVALUATION OF CROSS BREED HYBRIDS FOR BmBDV RESISTANCE THROUGH MOLECULAR MARKER ASSISTED SELECTION

Abstract

Bombyx mori bidensovirus (BmBDVs) are one of the causative agents of Flacherie disease which causes densonucleosis in the B.mori silkworm. In BmBDV, resistance or the non-susceptibility is governed by a single recessive gene called non-susceptibility to BmBDV (nsd-2). The deletion in nsd-2 gene is associated with the BmBDV resistance and hence can be used as a marker for molecular marker assisted breeding program. In the present study, cross breeds were developed by screening 17 multivoltine breeds popular among the breeders to develop hybrids for the Northeast regions of India. Out of 17 multivoltine, three showed presence of nsd-2 resistant allele in heterozygous/homozygous condition. Among the breeds which carry nsd-2 resistant allele, Lamerin breed showed complete homozygosity for nsd-2 resistant allele through marker assisted selection and showed complete resistance to BmBDV infection and was taken as female parent. Another productive bivoltine breed CSR2R resistant to BmBDV was developed through marker assisted backcrossing method was taken as a male parent. The control hybrids Lamerin, CSR2 as well as the BmBDV resistant LamerinR and CSR2R were further crossed to develop crossbreed and these hybrids were confirmed for BmBDV resistance through bioassay and absence of viral genome through conventional PCR.The BmBDV resistant hybrids showed >90% (90%) survivability compared to control susceptible hybrid with 10.66% survival post infection with the BmBDV. Further, the BmBDV resistant hybrids (LamerinR X CSR2R) also showed significant improvement in the pre cocoon and the post cocoon traits at par with the (LamerinXCSR2) and there was no deviation or compromise in the economic characters. Hence, the developed cross breeds with the disease resistant trait along with the improved qualitative and quantitative traits will enhance the productivity which can be successfully commercialized in Northeastern part of India and Lamerin can also be used as foundation cross in Multi x Bi hybrids (Crossbreeds).