Genetic variability in the coat protein gene of Potato virus X and the current relationship between phylogenetic placement and resistance groupings

The complete coat protein nucleotide sequences of 11 Potato virus X isolates from Australia and two from Britain were compared to those of 72 others. On phylogenetic analysis, clade I contained all 11 Australian sequences, and sub-clade II-1 contained the two new British sequences. Clade I isolates were from six different continents, but those in sub-clades II-1 and II-2 were only from Europe and the Americas, respectively. Clade I contained isolates in strain groups 1, 3 and 4, and sub-clades II-1 and II-2, isolates in strain groups 2 and 4. Thus, strain group 4 now occurs within both clades.