Nucleotide sequence diversity in Velvet tobacco mottle virus: a virus with a unique Australian pathosystem

Velvet tobacco mottle virus (VTMoV) is a naturally occurring mirid-transmitted sobemovirus of native velvet tobacco (Nicotiana velutina) plants in the Australian arid zone. We have sequenced the coding region of a typical field isolate of VTMoV (isolate I-17-04, satellite-plus) and show that it differed by nine polymorphisms from the previously sequenced atypical 'satellite-minus' variant VTMoV-K1 (represented here as L-K1-04), while retaining the same genomic and amino acid sequence motifs. We also report that although L-K1-04 was confirmed to be free of detectable satellite RNA by gel electrophoretic assay, the satellite sequence was detected in it by RT-PCR assay. Nucleotide sequence variation among the RNA-dependent RNA polymerase open reading frames of 15 field and laboratory isolates identified four phylogenetic groups, but these did not show a pattern related to site or time of sampling. This result would be consistent with nucleotide sequence variants of VTMoV being dispersed widely by migrating adult mirid vectors.