Morphology of BmNPV - polyhedra of Bombyx mori in Thailand

Abstract

Morphology of nucleopolyhedrovirus of Bombyx mori (BmNPV) was studied.
BmNPV causes grassery disease which is the most severe disease in Thai sericulture.
The aim of this study was to investigate the morphology of BmNPV in Thailand. The
BmNPV infected Thai silkworm larvae were surveyed and collected from 26 provinces. The
collected areas, divided into 4 regions, were the Northeastern: Nakhon Ratchasima,
Buriram, Surin, Si-SaKet, Ubon Ratchathani, Amnat Chareun, Roi Et, Mahasarakham, Khon
Kaen, Chaiyaphum, Udon Thani, Bung Karn, Loei and Sakon Nakhon. The Northern:
Phetchabool, Chiang Rai, Phayao, Kamphaeng Phet, Sukhothai, Phitsanulok and Tak. The
Center: Uthai Thani, Kanchanaburi and Ratchaburi. The Southern: Chumphon and Ranong.
The grassery infected silkworms were collected and BmNPV-polyhedra was harvested by
cutting the prolegs of the 4th and 5th instar larva. Haemolymph including BmNPV -
polyhedra was separated by centrifugation at 1957 x g for 5 minutes. The pellet of BmNPV
– polyhedra was suspended in distilled water. We examine the purity of polyhedral by
using light microscopy. The morphology of BmNPV-polyhedra was studied and prepared
by fixing in 2% of glutaradehyde at 4 °C and BmNPV-polyhedra were observed by scanning
electron microscopy (SEM) at a magnification of 10,000x. The results showed that the
morphology of BmNPV-polyhedra were 4 shapes: cuboidal, hexagonal, octagonal, and
globular. The globular and hexagonal shape were found in 100 % of silkworm collections
and the cuboidal and octagonal were present in 84.61% and 73.07%, respectively. The
result obtained from this study will be the basic information for the further virulence
determination of grassery disease caused BmNPV.