Causal agent of sharka disease: new and emerging events associated with Plum pox virus characterization

Plant RNA viruses have a high genetic variation potential due to the absence of proofreading activity in their RNA replicase. In addition to mutation, recombination is generally thought to be an important source of variability. Both evolutionary processes have contributed to the diversity of Plum pox virus (PPV). There are now six recognized subgroups, strains or serotypes of PPV (D, M, Rec, EA, C and W). Isolates belonging to the PPV‐Rec subgroup are derived from RNA recombination between PPV‐D and PPV‐M and occur frequently in various central and eastern European countries. The divergent isolate W3174 is a new and distinct strain of PPV, identified as PPV‐W. It is quite conceivable that, with time, other groups will be defined and that the present classification will need revision to accommodate additional PPV variability.