Abstract
BackgroundThe 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.ResultsThe 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.ConclusionsOn 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.
Highlights
The alphabaculoviruses are lethal pathogens of lepidopteran caterpillars including a polyphagous and globally recognized pest, Helicoverpa armigera (Hubner) infesting economically important agriculture crops worldwide
38 genes are reported to be conserved among all sequenced genomes of baculovirus till date, and these genes are assigned as core genes (Williams et al 2016; Blissard and Theilmann 2018)
Electron microscopy Morphology of the purified Occlusion bodies (OBs) extracted from individual larvae was studied under scanning electron microscope (SEM) (Model: FEI Quanta 250, The Netherlands) and transmission electron microscope (TEM) (Model: Jeol JEM 1400, Japan) at EM Unit-SAIF, CSIR-CDRI, Lucknow (India), and photographed at different magnifications
Summary
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 baculoviruses are regarded as potential biological control agents because of their safety to vertebrates, high pathogenicity, host-specificity, and ability to cause epizootics in the insect population. They have been reported worldwide from over 600 host species (Martignoni and Iwai 1986), mostly from the insect species of orders Lepidoptera, Diptera, and Hymenoptera (Herniou et al 2012). The genus Alphabaculovirus that included lepidopteran-specific nucleopolyhedroviruses (NPVs) is further classified into group I and group II NPVs, based on the presence of envelope fusion proteins in budded viruses, viz., GP64 and F protein, respectively (Lauzon et al 2006). Oligonucleotides that amplify partial sequences of baculovirus core genes, polyhedrin encoding a major
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