Genotypic divergence of three single nuclear polyhedrosis virus (SNPV) strains from the cabbage looper, Trichoplusia ni

• Published in: Biochemical systematics and ecology 1997-06, Vol.25 (4), p.287-295
• Main Authors: Del Rincón-Castro, Ma.Cristina, Ibarra, Jorge E.
• Format: Article
• Language: English
• ISSN: 0305-1978; 1873-2925
• DOI: 10.1016/S0305-1978(97)00002-1

Three singly-enveloped nuclear polyhedrosis virus strains of Trichoplusia ni (TnSNPV) from Mexico (LBIV-4), Canada (LBIV-8), and China (LBIV-10), were compared by their genome size, restriction patterns generated by endonucleases EcoRI, BamHI and HindIII, virulence measured by LC 50s, ultrastructure of polyhedra and virions, Southern hybridization analysis of complete genomes, protein content of virions and occlusion bodies (OBs), and specificity by bioassays against four other lepidopteran species. Genome size of strains LBIV-4, LBIV-8, and LBIV-10 was calculated at approximately 112, 119 and 106kb, respectively. Percentage similarity of restriction enzyme patterns between strains LBIV-4 and LBIV-8, LBIV-4 and LBIV-10, and LBIV-8 and LBIV-10 were 72, 46, and 51%, respectively, with sequence divergence estimated at 1.87, 4.55, and 3.83%, respectively. Virulence of strain LBIV-4 was 3.5 and 4.9 times greater than strains LBIV-8 and LBIV-10, respectively, while virulence of strain LBIV-8 was 1.4 times greater than strain LBIV-10. Southern analysis of each strain's genome and protein content of virions and OBs indicated very high similarity between the TnSNPV strains, with ultrastructure nearly identical in all the strains; none showed pathogenicity against any of the other lepidopteran species tested. Because of their high similarity and some distinctive genotypic differences, it is suggested that these strains represent divergent groups of viruses, with a common ancestor. Geographic isolation may be the cause of this divergence, as North American strains showed greater similarity among themselves than with the Chinese strain.