Characterization of the Helicoverpa Armigera Nucleopolyhedrovirus During Serial Passage in Cell Culture

Helicoverpa armigera nucleopolyhedrovirus (HearNPV) is highly pathogenic to the cotton bollworm, H. armigera. There have been several attempts to develop in vitro production of this virus, including the selection of high producing cell line. In order to evaluate the potential of in vitro methods of producing this virus on a large-scale, the virus was propagated in the H. armigera (HAPO2) and H. zea (HZ-AM1) cell lines and the correlation between the few polyhedra (FP) phenotype of HearNPV and the mutation in the polyhedrin (polh) and fp25k genes was analyzed. The many polyhedra (MP) phenotype was the predominant population of HearNPV for 3 passages in HZ-AM1 culture. The production of occlusion bodies (OBs) decreased with increasing passage number. The phenotypic observations on the HearNPV FP variants when this virus is serially passaged in HZ-AM1 cells suggest genomic changes occurring in the viral genes. A single point mutation resulting in an amino acid change was identified in the fp25k gene. This mutation could be correlated with the appearance of the FP phenotype with no relation to the polh gene. In contrast, serial passage in HAPO2 cells showed a slower accumulation of FP variants when compared to the use of HZ-AM1 cell line and no mutation was found in the fp25k gene. Therefore, HAPO2 cell line is a productive new cell line that will be useful for the scale-up process of HearNPV bioinsecticides.