Nucleotide Sequence Homologies among RNA Species of Strains of Tomato Black Ring Virus and Other Nepoviruses

Nucleotide sequences of the genome RNA species of four strains of tomato black ring virus (TBRV), two each from the Scottish and German serotypes, were compared by hybridization with complementary DNA copies. Within each serotype 90 ~ or more homology was observed between the corresponding RNA species of each pair of strains. Between serotypes greater differences were found, with 30 to 40~ of RNA-1 sequences and only about 10~ of RNA-2 sequences being common to all four strains. Hybridization reactions between RNA species and complementary DNA preparations representing different serotypes proceeded more slowly, and the hybrids melted at lower temperatures than those between homologous combinations, indicating that the apparently conserved sequences are similar, but not identical, in the two serotypes. Satellite RNA species from two TBRV strains in different serotypes had only about a quarter of their sequences in common. Limited nucleotide sequence homology was found between the genome RNA species of TBRV and those of the serologically distantly related grapevine chrome mosaic, cacao necrosis and artichoke Italian latent viruses, but not between TBRV RNA species and those of seven serologically unrelated nepoviruses.