Molecular markers in commercial Bombyx mori (Lepidoptera: Bombycidae) hybrids susceptible to multiple nucleopolyhedrovirus

The silkworm Bombyx mori L. is particularly susceptible to virus diseases, especially B. mori nucleopolyhedrovirus (BmNPV). Disease resistance, along with high productivity, are important selection criteria for developing commercial hybrids of B. mori. We used bioassays and molecular markers linked to susceptibility/resistance to baculovirus infection to analyze the response of commercial B. mori hybrids from two companies to a geographic isolate of B. mori multiple nucleopolyhedrovirus (BmMNPV) from Paraná state in Brazil. Both of these commercial lines were highly susceptible to BmMNPV, with death rates of 92 and 94%. A polymorphic fragment of approximately ~350 bp, associated with susceptibility, and an ~800-bp fragment, associated with resistance to BmMNPV, were detected in all specimens. An additional fragment of ~480 bp, recently identified by our research team as a BmMNPV genomic sequence, was detected in the infected silkworms and could be used as a molecular marker for the diagnosis of nucleopolyhedrovirus infection.