Biological characteristics of Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) isolated from the sericultural region of Guangxi

Abstract:

[Background] Silkworm (Bombyx mori) midgut polyhedrosis is a highly infectious and harmful viral disease caused by B. mori cytoplasmic polyhedrosis virus (BmCPV). Which virus has strong resistance, a wide host range, and is difficult to control and prevent. [Objective] To investigate the occurrence of silkworm midgut polyhedrosis in the sericultural region of Guangxi and study the pathogenicity, morphological characteristics, and molecular information of BmCPV, so as to provide a basis for the effective control of silkworm midgut polyhedrosis. [Methods] The anatomical and microscopic examinations of the diseased silkworm were combined to reveal the incidence of silkworm midgut polyhedrosis, and the median infectious concentration (IC₅₀) of BmCPV on silkworm was investigated via biological tests. The external morphology of BmCPVwas observed by optical microscopy and scanning electron microscopy, and the internal structure by transmission electron microscopy. PCR amplification and sequencing were employed to identify the BmCPV. [Results] Silkworm midgut polyhedrosis was prevalent in the sericultural region of Guangxi, with the incidence rate of 6.06% and 13.02% in Jinchengjiang and Donglan, respectively, and the highest incidence of 30.41%. Two BmCPV strains, BmCPV-J and BmCPV-D, were isolated from the diseased silkworm in the two sericultural regions, with the IC₅₀ of 4.88×10³ PIBs/mL and 1.63×10⁴ PIBs/mL, respectively, which indicated strong pathogenicity. BmCPV-J and BmCPV-D were hexagonal polyhedra with the diameters of 1.0-3.4 μm, differences in size between polyhedra, the spherical virion diameters of 30-50 nm, and spiny protuberances. PCR was conducted with the primers designed based on the RNA replicase gene of BmCPV. The fragment of BmCPV-J was identical with that of BmCPV reference strain, while that of BmCPV-D had two base differences. [Conclusion] Silkworm midgut polyhedrosis is a serious disease in the sericultural region of Guangxi, and its pathogen has strong infectivity and wide distribution. BmCPV-J and BmCPV-D with typical characteristics of CPV which belong to BmCPV. The results provide an important basis for the effective control of silkworm midgut polyhedrosis.