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Sericultural production is seriously influenced by the blood pathogens of grasserie, Bombyx mori nucleopolyhedrovirus (BmNPV). To investigate the infectious condition and define an effective control method for BmNPV. 233 from 240 suspected samples infected with BmNPV were detected using PCR identification. One sample was selected from each county in the positive sample collection area, 56 isolates of which were used as experimental objects. The homology of the bro-d nucleotide sequence was at least 91% among the 56 BmNPV isolates. However, the conserved 7 amino acids (percentage of amino acid constant sites, PAACS) at the position 217-224 were absent for YNQJLL001 and YNZTQJ074 pandemic isolates. Phylogenetic tree analysis of bro-d gene separated the BmNPV isolates from Yunnan into 4 main clades: I, II, III, and IV. Clade I was the dominant clade containing 32 local epidemic isolates. Clades II, III, and IV contained 5, 16, and 3 pandemic isolates, respectively. Geographical distribution of clade I in Yunnan showed a concentrated pattern, while the remaining members of the other three clades depicted no direct contact in relation to their locations. This study may provide valuable molecular types on BmNPV isolate distribution in the silkworm-raising regions, also be helpful for evaluating BmNPV pathogenesis and epidemic situations in the Yunnan sericulture region. [ABSTRACT FROM AUTHOR]

Bombyx mori nucleopolyhedrovirus (BmNPV) is a silkworm pathogen that causes serious economic losses in sericulture. In this study, a new BmNPV strain, designated as BmNPV-YN1, from Yunnan (China), was isolated and identified through molecular identification. Sequence analysis results revealed that polyhedrin (polh) presented the highest identity among various BmNPVs; this gene indicated that BmNPV-YN1 is a BmNPV strain. The baculovirus repeated-ORF (bro) genes of this isolate were different from those of six BmNPV strains (BmNPV-T3, BmNPV-ZJ, BmNPV-GX, BmNPV-India, BmNPV-Cubic, and BmNPV-Brazilian). The BmNPV-YN1 bro family includes bro-a, bro-b, broc, bro-d, and bro-e, which are similar to those of BmNPV-T3. Sequence alignment results further showed the differences in the composition and sequences of the bro family members among various strains. The bro-d sequences were also phylogenetically analysed. Results demonstrate that BmNPV-YN1, BmNPV-Cubic, and BmNPV-India are closely related. Despite this close relationship, BmNPV-YN1 belongs to a distinct cluster. The BmNPV DNA was subjected to restriction endonuclease analysis and the obtained results provided additional evidence supporting the identity of the novel BmNPV-YN1 strain. Indeed, BmNPV-YN1 isolated from Yunnan is a new BmNPV strain. The proposed method can be used to rapidly and accurately detect and identify BmNPVs strains. [ABSTRACT FROM AUTHOR]