The polyhedral membrane does not protect polyhedra of AcMNPV against inactivation on greenhouse chrysanthemum

Polyhedral inactivation of wild-type AcMNPV and an AcMNPV mutant lacking the gene for the polyhedral membrane pi protein (AcMNPV-Delta pp34) was studied on greenhouse chrysanthetnum. It was hypothesized that polyhedra without a polyhedral membrane might be more susceptible to inactivation on plants. The density of infectious polyhedra of both viruses on the leaf surface decreased in time in a near-exponential fashion. The inactivation curves suggested the presence of two distinct fractions of polyhedra with differences in persistence. One function of polyhedra is not inactivated at all, whereas the other fraction is inactivated in an exponential fashion. Relative inactivation rates of the inactivated polyhedra fraction for wild-type AcMNPV and AcMNPV-Delta pp34 were 0.16 and 0.13 per day, respectively, which is not significantly different. After 28 days on leaves in a greenhouse, both viruses still showed residual infectivity. The fi action of residual infectious polyhedra were not significantly different and amounted to approximately 20% of the original density for both wild-type AcMNPV and AcMNPY-Delta pp34. Therefore, the polyhedral membrane does not protect polyhedra against inactivation on greenhouse chrysanthemum.