Phylogenetic Reconstruction from Sequences of Plum Pox Virus Samples Collected in the United States Points to Multiple Independent Introductions

Plum pox virus (PPV) is a serious threat to peach, plum, and other stone fruit production worldwide. It has spread from Europe to most major Prunus cultivation areas worldwide; the major exception is the United States. PPV was discovered in Pennsylvania in 1999 and, after a massive survey effort, declared eradicated 20 years later, following the last positive find in 2015. In this study, genome sequences of six PPV finds from the eradication effort are presented. They all belong to strain D; however, there is up to 1.8% nucleotide sequence diversity among them. Phylogenetic analysis reveals that most previously published U.S. PPV sequences and two of the ones reported here are highly similar, consistent with all of them arising from a single introduction to south-central Pennsylvania. However, four of the PPV sequences reported here are significantly different from ones in the Pennsylvania epicenter and are likely to be separate, independent introductions of PPV into the United States. Because there appear to have been at least six separate introductions of PPV into the United States, continued diagnostic surveys will likely be required to keep U.S. agriculture free of this damaging virus. [Formula: see text]