The microbes such as viruses, microsporidia, bacteria and fungi cause the infectious diseases in silkworm. Among the infectious diseases, the flacherie prevails during all the seasons and is caused by Bombyx mori cytoplasmic polyhedrisis virus (BmCPV), Bombyx mori infectious flacherie virus (BmIFV) and Bombyx mori densonucleosis virus (BmDNV) individually or in association with one or both other viruses. The estimated cocoon crop loss is as 11.486, 14.864 and 14.500 kg/100 dfls during summer, winter and rainy seasons respectively in India. The cumulative mortality rate of popular multivoltine breeds viz., Pure Mysore, Nistari C.Nichi and ND7 indicated that larvae inoculated with a high dose of 1 × 10-2.0, 1 × 10-4.5 BmIFV, Pure Mysore is showing 79.34 and 60.33% mortality. In case of Nistari, mortality rate is 72.50 and 60.00%, ND7, 78.75 and 50.67% and C. Nichi showing 49.67 and 42.33% mortality rate respectively. The cumulative mortality rate of popular bivoltine breeds viz., CSR2, CSR4, CSR50, CSR51 revealed that larvae inoculated with high dose of 1 × 10-2. , 1 × 10-4.5 BmIFV, CSR2 is showing 83.00 and 61.30% mortality. In case of CSR4, mortality rate is79.50 and 50.33%, in CSR50 it is 57.50 and 43.67% and CSR51 showing 65.50 and 48.33% mortality rate respectively. The overall result exhibited that among multivoltines, C.Nichi with 42.33% mortality and in bivoltine category, CSR50 showing least mortality of 43.67% considered to be most tolerant breeds against BmIFV even at high dose. It was also reported in earlier studies that in tolerant breeds, the mid gut epithelial layer is found to be multi layered and having regenerative capacity to withstand the pathogen infection. Thus the present study indicated that the resistant and popular multivoltine, bivoltine breeds can be used as potential breeding resource materials against the BmIFV disease.
