First molecular characterization of plum pox virus strains in stone fruits of Tuscany (Central Italy)

Plum pox virus (PPV) a potyvirus in the family Potyviridae, is the etiologic agent of sharka, the worldwide most important and detrimental viral disease of stone fruits (genus Prunus). Although PPV was identified in Italy already in the 1970s and it has been largely reported in almost all Italian regions, a broad investigation and genetic characterization of PPV isolates was lacking in most of them, including Tuscany (Central Italy). To address this knowledge gap, in 2020 and 2021, field surveys were carried out in 80 commercial Tuscany orchards and a total of 690 leaf samples were collected from different Prunus species. PPV was identified in 25 and 12 peach and plum samples, respectively (more than 5% of tested samples), whereas no positive samples were reported in apricot. Eighteen of the 37 PPV positive samples showed mixed infections with other viruses and viroids, mostly Prunus necrotic ringspot virus in plum and peach latent mosaic viroid in peach. Molecular typing of PPV infected samples generated NIb/CP amplicons corresponding to PPV-Marcus (M) or PPV-Recombinant (Rec) strains. Furthermore, starting from the identification of eight PPV nucleotide sequences (among which five and two new PPV-M and PPV-Rec isolates, respectively), this study firstly identified the PPV-Mb subgroup in Italy, which was even prevalent than PPV-Ma. Finally, PPV-Rec isolates resulted phylogenetically close to Italian and Turkish isolates previously detected. Overall, the results here presented represent an important step to fill knowledge gaps about PPV in Tuscany, and we believe it may encourage other similar research to achieve more accurate data on PPV populations at both national and international levels.