Abstract: SpltMNPV X₁₇ was isolated from the stock collected in Ogasawara Island, Japan, by in vivo cloning techniques. In order to reveal its genotype, the primer was designed according to the complete genome sequence deposited in GenBank under accession no. NC_011616. The polyhedrin gene of X₁₇ was amplified by PCR, and then the neighbor-joining tree based on nucleotide sequences of the polyhedron gene between SpltMNPV different genotypes including X₁₇ and 37 NPVs was constructed. The phylogenetic tree indicated that SpltMNPVs were broadly divided into three groups, i.e., SpliNPV (A) type, SpltMNPV (B) type and SeMNPV (C) type, which is consistent with other reported research results by DNA restriction endonuclease analysis. X₁₇, SpltMNPV-1 and SpltMNPVⅡ clustered into one clade, which was genetically away from the other SpltMNPV genotypes and belonged to SpltMNPV C genotype. Moreover, the genes 38.7kD, Lef-1, Lef-9, fp, p10 and p74 of X₁₇ were also cloned by PCR amplification, and homologous analyses of the genes between X₁₇ and SpltMNPV, SpltMNPVⅡ, SeMNPV and SfNPV were performed. The results showed that based on the six cloned ORFs the homology between X₁₇ and SpltMNPV is the lowest. The identity for amino acid sequence of the late expression factor 9 (lef-9) is the highest (69%), but that of the 38.7 kD amino acid sequence is only 26%. The homology of the most genes amplified between X₁₇ and SpltMNPVⅡor SeMNPV is higher than that between X₁₇ and another NPV analyzed here. The identities of the fp25K amino acid sequence between X₁₇ and SpltMNPVⅡor SeMNPV are both high (up to 95% and 96%, respectively), but that of the 38.7kD amino acid sequence is the lowest of the six ORFs (64%). It is reasonably concluded that X₁₇ is a new strain of SpltMNPV C gentype, named as SpltMNPVⅡ-1. This study provides some theoretical basis for further study and utilization of X₁₇ strain.  

Key words: Spodoptera litura multinucleocapsid nucleopolyhedrovirus (SpltMNPV), C genotype, gene, homology, phylogeny