Egyptian Journal of Biological Pest Control (Sep 2019)
Genetic diversity among different geographical isolates of the gram pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) nucleopolyhedrosis virus (HearNPV)
Abstract
Abstract The gram pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), is infected by nucleopolyhedrosis virus (HearNPV), which is the most promising microbial biocontrol agent of the pest. A genetic diversity analysis of geographically distinct isolates of HearNPV was done, using the polyhedrin (polh) gene of the viruses that encodes a major structural protein of the occlusion bodies. The gene was amplified and isolated from eight Indian isolates, using the polymerase chain reaction (PCR). These sequences were compared with the polh genes of other HearNPV from different geographical regions of the world. A phylogenetic tree was constructed, using polh nucleotide/deduced amino acid sequences to know their genetic relatedness. The polh gene of isolates originating from nearby locations clustered together with the gene of isolates in the present study; however, some showed relatedness with gene isolate from other geographically distinct isolates, with respect to the genetic distances among them. The Indian isolate (Ban-PDBC-In) shared lower genetic distance of 0.0020 to 0.0040 substitutions per site with the Spanish isolates SP1A-Sp and SP1B-Sp and clustered in one group based on nucleotide sequences. The isolates showed different a clustering pattern in phylogenetic tree based on deduced amino acid sequences than that of the nucleotide sequences. The overall genetic distances between polh nucleotides ranged from 0.0000 to 0.0203 substitutions per site, while it was 0.0000 to 0.0121 between deduced amino acid sequences. Among different geographical groups of isolates, the Indian group showed the highest genetic diversity based on both polh nucleotide (0.0070 ± 0.0002 substitutions per site) and deduced amino acid (0.0057 ± 0.0003 substitutions per site) sequences among different groups of geographical isolates. A diversity analysis of virus isolates can aid in the selection and identification of virulent virus isolates for the development of a virus-based bio-pesticide formulation.
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