Genetic structure of a Spodoptera frugiperda nucleopolyhedrovirus population: high prevalence of deletion genotypes.
A Nicaraguan field isolate (SfNIC) of Spodoptera frugiperda nucleopolyhedrovirus was purified by plaque assay on Sf9 cells. Nine distinct genotypes, A to I, were identified by their restriction endonuclease profiles. Variant SfNIC-B was selected as the standard because its restriction profile corresponded to that of the wild-type isolate. Physical maps were generated for each of the variants. The differences between variants and the SfNIC-B standard were confined to the region between map units 9 and 32.5. This region included PstI-G, PstI-F, PstI-L, PstI-K and EcoRI-L fragments. Eight genotypes presented a deletion in their genome compared with SfNIC-B. Occlusion body-derived virions of SfNIC-C, -D and -G accounted for 41% of plaque-purified clones. These variants were not infectious per os but retained infectivity by injection into S. frugiperda larvae. Median 50% lethal concentration values for the other cloned genotypes were significantly higher than that of the wild type. The variants also differed in their speed of kill. Noninfectious variants SfNIC-C and -D lacked the pif and pif-2 genes. Infectivity was restored to these variants by plasmid rescue with a plasmid comprising both pif and pif-2. Transcription of an SfNIC-G gene was detected by reverse transcription-PCR in insects, but no fatal disease developed. Transcription was not detected in SfNIC-C or -D-inoculated larvae. We conclude that the SfNIC population presents high levels of genetic diversity, localized to a 17-kb region containing pif and pif-2, and that interactions among complete and deleted genotypic variants will likely influence the capacity of this virus to control insect pests.
Simón
Oihane
O
Departamento de Producción Agraria, Universidad Pública de Navarra, 31006 Pamplona, Spain. pcm92@unavarra.es
Williams
Trevor
T
López-Ferber
Miguel
M
Caballero
Primitivo
P
D000818:Animals; D003001:Cloning, Molecular; D017353:Gene Deletion; D005814:Genes, Viral / Q000235:genetics*; D014644:Genetic Variation / Q000235:genetics; D005838:Genotype; D017924:Nucleopolyhedroviruses / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D015183:Restriction Mapping; D018411:Spodoptera / Q000821:virology*