The effects of in vivo passaging, solar radiation exposure and inoculum dose on the genetic diversity of Helicoverpa armigera nucleopolyhedrovirus
Date
2017
Authors
Kitchin, Dale John
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Abstract
The nucleopolyhedroviruses (NPVs) are a group of entomopathogenic viruses, with large
double-stranded DNA genomes, which belong to the Baculoviridae family. Considerable genetic
diversity is known to exist within NPV populations, with a number of studies having shown that
NPV populations consist of multiple genotypes. Studies have also shown that the genotypic
composition of NPV populations can vary between different host individuals and geographical
locations. Yet, how this genetic diversity is generated and maintained in NPV populations over
successive infections is not fully understood. In this study, a denaturing gradient gel electrophoresis
(DGGE) assay and deep amplicon sequencing were used to assess the effects of serial in vivo
passaging, pre-infection exposure to solar radiation and occlusion derived virion (ODV) inoculum
dose on the genetic diversity of Helicoverpa armigera nucleopolyhedrovirus (HearNPV)
populations within regions of the DNA polymerase and me53 genes. The serial in vivo passaging of
a HearNPV population, using a high OB inoculum dose (LD90 × 5), did not result in a common or
similar genotypic composition in the 125 third passage HearNPV populations isolated from
individual host insects. Shifts in the relative abundance of inoculum genetic variants and the
generation of novel genetic variants caused the HearNPV populations isolated from individual
insects to diverge in genetic variant composition over the three serial in vivo passages. Although
pre-infection exposure of HearNPV OBs to solar radiation did not increase the frequency at which
novel genetic variants were generated over the course of an infection, it did appear to contribute to
the divergence in genetic variant composition of HearNPV populations over in vivo passages. It was
also observed that the higher the ODV inoculum dose the greater the probability that the genetic
variant composition of the post-passage HearNPV population would resemble that of the inoculum
population. Overall it was shown that in vivo passaging, pre-infection exposure of OBs to solar
radiation and ODV inoculum dose all affect the genotypic composition of HearNPV populations.
The findings of this study contribute to the understanding of the factors that affect the generation
and maintenance of HearNPV genetic diversity over the course of an infection and provide insights
into how the genetic diversity between distant geographical HearNPV isolates may develop in the
field.
Description
A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg 2017
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Citation
Kitchin, Dale John, (2017) The effects of in vivo passaging, solar radiation exposure and inoculum dose on the genetic diversity of Helicoverpa armigera nucleopolyhedrovirus, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/26508