In vivo and in vitro characterization of several isolates of spodoptera exigua nuclear polyhedrosis virus.

Spodoptera exigua nuclear polyhedrosis viruses (SeNPVs), isolated form five geographically distinct regions of Japan and Thailand, were characterized by their DNA restriction endonuclease pattern, level of virus production in a continuous cell line of S. exigua and biological activity to S. exigua larvae. The EcoRI and PstI fragments exhibited similar overall patterns with minor differences. Digestion of virus DNA from a plaque-purified isolate, SeNPV-I1, with PstI yielded 14 fragments and the estimated genome size was approximately 123 kbp. The SeNPV wild isolate from Kagoshima, SeNPV-KW, showed the highest yield of extracellular virus (ECV) in the Se301 cell line of S. exigua among five wild isolates, but there was no significant difference in the level of polyhedral inclusion body (PIB) formation. In comparative studies of biological activity using 2nd-instar S. exigua larvae, SeNPV-KW had the highest virulence with an LD50 value of 3.0 PIBs per larva. When 16 clones, plaque-purified from the Isahaya isolate, SeNPV-IW, were examined for genetic relatedness, seven distinct EcoRI patterns were observed, indicating that SeNPV-IW wild isolate consisted of a mixture of different genotypes.