Isolation, Complementation and Partial Characterization of Temperature-sensitive Mutants of the Baculovirus Hyphantria Cunea Nuclear Polyhedrosis Virus

Twelve temperature-sensitive mutants were isolated from Hyphantria cunea nuclear polyhedrosis virus grown in Spodoptera frugiperda cells and were sorted into four groups by their properties in plaque assays at the non-permissive temperature (32 °C). The phenotypes of the four groups were as follows: (i) failure to make polyhedra, (ii) few polyhedra formed, (iii) reduced plaquing efficiency, (iv) small plaque size. Ten mutants had reduced plaque size and polyhedra formation at 32 °C. One mutant formed plaques without polyhedra, had a reduced infectious virus titre at 32 °C and also showed a defect in late gene function. Two mutants formed small plaques with few polyhedra and were temperature-sensitive with respect to production of extracellular non-occluded virions at 32 °C. Other phenotypes were also distinguished. The formation of polyhedra by all the mutants was 2 to 4 h faster at 32 °C than at 25 °C. After temperature shift-up from 25 °C to 32 °C at 12 h post-infection polyhedron formation was still 2 to 4 h faster. Complementation analyses based on polyhedron formation in double infections at 32 °C distinguished four complementation groups.