A host range variant of Autographa californica nuclear polyhedrosis virus: identification and specificity studies in Spodoptera frugiperda cells

A new, host range variant of Autographa californica nuclear polyhedrosis virus, designated Gl, grew premissively in the Trichoplusia ni cell line (TN368), but only semipermissively in the Spodoptera frugiperda cell line (IPLB-SF-21,VE). This was in contrast to the previously studied Autographa californica Ll isolate, which grew permissively in both cell lines. This paper compares the growth patterns of the new variant, AcGl, to AcLl, with respect to the production of extracellular and intracellular non-occluded viruses and polyhedral inclusion bodies in both cell lines. The AcGl variant demonstrated a 50% reduction in SF cells of inclusion bodies, extracellular and intracellular non-occluded virus, compared to AcLl. Plating efficiency results showed a three hundred fold lower titer for AcGl in SF cells than AcLl. At 33 C the AcGl variant produced 75% fewer SF cells containing inclusion bodies, indicating temperature sensitivity. The DNA of both viruses were studied by endonuclease digestion with EcoRI, Hind III, and Bam HI. Based on DNA fragment migration, AcGl demonstrated a 7% sequence divergence by Upholt's method from AcLl. A tentative genetic map of AcGl was constructed based on close visual comparison of the restriction patterns with previous work done on AcLl in an effort to locate regions of the AcGl genome responsible for the observed growth differences in cell culture. The analysis showed that host range modifications were likely in the 25-30% and 76-860 regions of the AcLl map (MilIer and Dawes, 1979). These results indicated that AcGl was a host range mutant of wild type AcLl, as it encountered infection block(s) in SF cells. The nature of this block(s) occurred sonnet and budding in viral replication.