GENOTYPIC DIVERGENCE OF 3 SINGLE NUCLEAR POLYHEDROSIS-VIRUS (SNPV) STRAINS FROM THE CABBAGE-LOOPER, TRICHOPLUSIA NI

Three singly-enveloped nuclear polyhedrosis virus strains of Trichoplu sia ni (TnSNPV) from Mexico (LBIV-4), Canada (LBIV-8), and China (LBIV -10), were compared by their genome size, restriction patterns generat ed by endonucleases EcoRI, BamHI and HindIII, virulence measured by LC (50)s, ultrastructure of polyhedra and virions, Southern hybridization analysis of complete genomes, protein content of virions and occlusio n bodies (OBs), and specificity by bioassays against four other lepido pteran species. Genome size of strains LBIV-4, LBIV-8, and LBIV-10 was calculated at approximately 112, 119 and 106 kb, respectively. Percen tage 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, an d 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 t imes greater than strains LBIV-8 and LBIV-10, respectively, while viru lence of strain LBIV-8 was 1.4 times greater than strain LBIV-10. Sout hern analysis of each strain's genome and protein content of virions a nd OBs indicated very high similarity between the TnSNPV strains, with ultrastructure nearly identical in all the strains; none showed patho genicity 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 virus es, with a common ancestor. Geographic isolation may be the cause of t his divergence, as North American strains showed greater similarity am ong themselves than with the Chinese strain. (C) 1997 Elsevier Science Ltd.