The phylogeny of Turnip mosaic virus; comparisons of 38 genomic sequences reveal a Eurasian origin and a recent 'emergence' in east Asia

The genomes of a representative world-wide collection of 32 Turnip mosaic virus (TuMV) isolates were sequenced and these, together with six previously reported sequences, were analysed. At least one-fifth of the sequences were recombinant. In phylogenetic analyses, using genomic sequences of Japanese yam mosaic virus as an outgroup, the TuMV sequences that did not show clear recombination formed a monophyletic group with four well-supported lineages. These groupings correlated with differences in pathogenicity and provenance; the sister group to all others was of Eurasian B-strain isolates from non-brassicas, and probably represents the ancestral TuMV population, and the most recently 'emerged' branch of the population was probably that of the BR-strain isolates found only in east Asia. Eight isolates, all from east Asia, were clear recombinants, probably the progeny of recent recombination events, whereas a similar number, from other parts of the world, were seemingly older recombinants. This difference indicates that the presence of clear recombinants in a subpopulation may be a molecular signature of a recent 'emergence'.