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Applied and Environmental Microbiology, August 2005, p. 4254-4262, Vol. 71, No. 8
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.8.4254-4262.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Functional Importance of Deletion Mutant Genotypes in an Insect Nucleopolyhedrovirus Population

Departamento de Producción Agraria, Universidad Pública de Navarra, 31006 Pamplona, Spain,¹ Laboratoire de Pathologie Comparée, UR 1231 INRA, 30380 Saint Christol les Alès, France²

Received 22 October 2004/ Accepted 3 March 2005

A Nicaraguan isolate of a nucleopolyhedrovirus (SfNIC) that attacks the fall armyworm, Spodoptera frugiperda, survives as a mixture of nine genotypes (SfNIC A to I) that all present genomic deletions, except variant B (complete genotype). Sequencing of cloned restriction fragments revealed that genotypic variants lack between 5 and 16 of the open reading frames present in a contiguous sequence of 18 kb of the SfNIC genome. The absence of oral infectivity of SfNIC-C and -D variants is related to the deletion of the pif and/or pif-2 gene, while that of SfNIC-G remains unexplained. The presence of open reading frame 10, homolog of Se030, also appeared to influence pathogenicity in certain variants. Previous studies demonstrated a significant positive interaction between genotypes B and C. We compared the median lethal concentration of single genotypes (A, B, C, D, and F) and co-occluded genotype mixtures (B+A, B+D, B+F, A+C, and F+C in a 3:1 ratio). Mixtures B+A and B+D showed increased pathogenicity, although only B+D restored the activity of the mixture to that of the natural population. Mixtures of two deletion variants (A+C and F+C) did not show interactions in pathogenicity. We conclude that minority genotypes have an important influence on the overall pathogenicity of the population. These results clearly demonstrate the value of retaining genotypic diversity in virus-based bioinsecticides.

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