Causal agent of sharka disease: historical perspective and current status of Plum pox virus strains

Abstract

Knowledge of the existence of strains or types of Plum pox virus (PPV), defined as monophyletic groups of closely related isolates sharing similar properties, has gradually emerged. Early attempts illustrated both the interest and the limits of biological properties for discrimination of isolates but in the late 1970s gel‐immunodiffusion assays allowed the grouping of PPV isolates into two serogroups typified by the Dideron (D) and Marcus (M) isolates. Technical difficulties, however, limited the widespread use of this approach and only in the early 1990s, with the availability of more discriminating and higher throughput techniques, did it become clear that PPV isolates could be allocated into two major groups. This led to the description of the strains, or types, PPV‐D and PPV‐M. Following this, distant PPV isolates typifying other strains such as El Amar (PPV‐EA), Cherry (PPV‐C) or Winona (PPV‐W) were identified, as well as the widespread group of recombinants known as PPV‐Rec. Each of the six known strains or types can now be identified using a range of serological or molecular techniques. However, their evolutionary history and, in particular, the reason for the wide prevalence of the PPV‐D, ‐M and ‐Rec types relative to PPV‐EA, ‐C or ‐W is still a matter of speculation.