Characterization of alphabaculovirus: HearNPV-IIPR05 isolate infecting Helicoverpa armigera (Hubner) larvae

Abstract

Abstract Background The alphabaculoviruses are lethal pathogens of lepidopteran caterpillars including a polyphagous and globally recognized pest, Helicoverpa armigera (Hubner) infesting economically important agriculture crops worldwide. The biological and molecular characterizations of indigenous nucleopolyhedrovirus of the genus Alphabaculovirus isolated from H. armigera in chickpea fields are described. Results The virulence of virus isolate was tested in 3rd instar H. armigera larvae, and LC50 (median lethal concentration) was estimated to be 2.69 × 104 OBs ml−1. The ST50 (median survival time) was 4 days post-inoculation, when the 3rd instar H. armigera larvae were inoculated by OB (occlusion body) concentration equivalent to LC90. An average incubation period of the virus isolate in 3rd instar ranged between 4 and 6 days post-inoculation. The OBs of a virus isolate appeared irregular in shape and variable in size with diameter ranging from 0.57 to 1.46 μm on the longest edge and average of 1.071 ± 0.068 μm (mean ± SE). On the basis of phylogenetic analysis of polh, pif-1, and lef-8 genes, the isolate was found to be a member of the genus Alphabaculovirus. The isolate showed a genetic affinity with species of group II Alphabaculoviruses and appeared to be a group II NPV. Conclusions On the basis of molecular phylogeny and associated host insect, this indigenous isolate was designated as HearNPV-IIPR05 isolate, which could be a potential candidate for the biological control of H. armigera infesting legumes and other commercial crops.

Keywords

• Alphabaculovirus
• Nucleopolyhedrovirus
• Helicoverpa armigera
• Phylogeny
• Virulence
• Biological control