Isolation of an Adoxophyes orana granulovirus (AdorGV) occlusion body morphology mutant: biological activity, genome sequence and relationship to other isolates of AdorGV.

A granulovirus (GV) producing occlusion bodies (OBs) with an unusual appearance was isolated from Adoxophyes spp. larvae in the field. Ultrastructural observations revealed that its OBs were significantly larger and cuboidal in shape, rather than the standard ovo-cylindrical shape typical of GVs. N-terminal amino acid sequence analysis of the OB matrix protein from this virus suggested that this new isolate was a variant of Adoxophyes orana granulovirus (AdorGV). Bioassays of this GV (termed AdorGV-M) and an English isolate of AdorGV (termed AdorGV-E) indicated that the two isolates were equally pathogenic against larvae of Adoxophyes honmai. However, AdorGV-M retained more infectivity towards larvae after irradiation with UV light than did AdorGV-E. Sequencing and analysis of the AdorGV-M genome revealed little sequence divergence between this isolate and AdorGV-E. Comparison of selected genes among the two AdorGV isolates and other Japanese AdorGV isolates revealed differences that may account for the unusual OB morphology of AdorGV-M.