Biological and molecular characterization of two Anticarsia gemmatalis multiple nucleopolyhedrovirus clones exhibiting contrasting virulence

Abstract

Baculovirus natural populations are known to be genetically heterogeneous and such genotypic diversity could have implications in the performance of biocontrol agents. The Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) has been widely used to control the velvetbean caterpillar, Anticarsia gemmatalis, in Brazil. In the present work, morphological and molecular analyses as well as the biological activity of AgMNPV genotypes derived from a Brazilian field isolate (AgMNPV-79) were carried out. The existence of genotypic variants in the population was confirmed by DNA restriction analysis. Although difference in virulence was observed among the variants, the most (Ag79-01) and the least (AgL-16) virulent clones do not show any morphological and cytopathological changes when compared to the most studied isolate (AgMNPV-2D). The complete genome analysis of the two viral clones showed the presence of single open reading frames (ORFs) of the pe-38 and he65 genes, which contrasts with the two split ORFs present in the genome of the AgMNPV-2D isolate. The viral clone AgL-16 has many variations in the ie-2 and pe-38 genes, which are transcription regulatory genes responsible for the regulation of viral early gene expression during insect cell infection. Furthermore, other genes showed alterations like the odv-e56, which have an essential role in the maturation and envelopment of the ODVs, and bro-a and bro-b genes which were fused to form a single ORF. For the Ag79-01, although the total number of single nucleotide variants (SNVs) was more prominent in the pe-38 gene, its genome showed very few modifications in comparison to the AgMNPV-2D genome.