Schneider: plum pox virus in the USA
Plum pox virus in the USA: Not all viruses are created equal
William L. Schneider
Plum pox virus (PPV) is a major pathogen of Prunus worldwide. In 1999 the associated disease was first identified in Pennsylvania, and the following year the disease was found in Canada. In 2006 the disease was found in upper New York and in one isolated location in Michigan. All of the isolates found in Pennsylvania and New York are classified as D strain isolates, and genetically they are more closely related to other western hemisphere D strain isolates than D strains from Europe. The levels of genetic identity for the Pennsylvania PPV isolates were 98-99% within the state, 96-98% with other western hemisphere isolates, and 93-98% with all other D strain isolates. Despite the close genetic relationship, there was considerable phenotypic variation both among Pennsylvania PPV isolates and between Pennsylvania PPV-D and European PPV-D. One subset of the Pennsylvania PPV isolates had higher titers, a broader host range and was more aphid transmissible than the other subset of Pennsylvania PPV isolates and European PPV-D isolates. This indicates that minor genetic changes are capable of generating significant phenotypic changes, and that as new outbreaks of PPV occur it is critical to characterize the isolate both genetically and biologically, rather than assuming that a new outbreak will follow patterns typical of genetically related PPV isolates. The Pennsylvania isolates of PPV were also fully capable of infecting two varieties of almond (Prunus dulcis cvs. “Butte” and “Mission”) when inoculated by aphids.