Submitted to: Journal of General Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/22/2007
Publication Date: 3/1/2008
Citation: Harrison, R.L., Puttler, B., Popham, H.J. 2008. Genomic sequence analysis of a fast-killing isolate of the Spodoptera frugiperda multiple nucleopolyhedrovirus. Journal of General Virology. 89:775-790. Interpretive Summary: Insect pests cause billions of dollars of damage to crops each year. The use of chemical insecticides to control insect pests can have negative ecological, environmental, and health consequences. Baculoviruses are a group of insect viruses that can be used for biologically-based insect control without the problems of chemical insecticides. However, the success of baculoviruses as control agents is partially limited by their slow speed of action against insect pests. A more complete understanding of the genetic factors regulating baculovirus insecticidal activity and speed of kill is necessary for improving their scope and performance as biopesticides. In this study, a new baculovirus was isolated from an insect pest called the fall armyworm. This baculovirus was found to kill fall armyworm larvae very rapidly. The entire DNA sequence of this virus was determined and analyzed. Features of the DNA sequence that may contribute to this virus’s insecticidal activity and rapid speed of kill were documented. The information in this study provides clues for how to develop baculovirus strains with enhanced insecticidal activity. Baculoviruses have a wide range of applications in addition to their use as biopesticides, and this study will be of interest to scientists in academia, government, and industry who work with this group of viruses.
Technical Abstract: Six clones of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) were plaque-purified from field isolates collected in Missouri, USA. In bioassays, four of the plaque-purified isolates killed neonate S. frugiperda larvae more rapidly than the field isolates from which they were derived, with LT50s ranging from 34.4 to 49.7 hours post-infection. The complete genomic sequence of one of these isolates, SfMNPV-3AP2, was determined and analyzed. The SfMNPV-3AP2 genome was 131,330 bp with a 40.2% G+C content. One hundred forty-four open reading frames (ORFs) were identified and examined, including the set of 62 genes in common among lepidopteran nucleopolyhedrovirus genomes. Comparison of ORF content, order, and predicted amino acid sequences with other nucleopolyhedoviruses indicated that SfMNPV was part of a cluster of viruses within NPV group II that includes NPVs isolated from Spodoptera, Agrotis, and Mamestra host species. SfMNPV-3AP2 shared a high degree of nucleotide sequence similarity with partial sequences from other SfMNPV isolates. Comparison of the SfMNPV-3AP2 genome sequence with a partial sequence from a Brazilian isolate of SfMNPV revealed that SfMNPV-3AP2 contains a deletion that removed parts of ORF sf27 and the gene encoding ecdysteroid UDP-glucosyltransferase (egt). An examination of the egt region in the other isolates revealed that the other five SfMNPV clones also contained deletions of varying length in this region. Variant genotypes with deletions extending around the egt gene have been reported previously from a Nicaraguan field isolate of SfMNPV, suggesting that the presence of such variants is a common feature of SfMNPV populations.