First Report of the Presence of Plum pox virus Rec Strain in France.

Plum pox virus (PPV) is the most detrimental virus in stone fruit crops (Prunus sp.). At least nine monophyletic PPV strains are recognized, three of which, PPV-D, PPV-M, and PPV-Rec, have broad distributions (2). PPV-Rec is characterized by a unique founding recombination event and has been reported mostly from Central and South-Central Europe (2). It is generally considered poorly adapted to peach, and the weak and transient symptoms it causes in the GF305 peach seedling indicator may complicate its biological detection (2). During surveys in the Alsace region of France in spring 2013, a plum orchard with trees (Prunus domestica cv. Quetsche d'Alsace 3066) showing dubious leaf symptoms possibly reminiscent of PPV infection was identified. Testing of material from this plant by ELISA (Bioreba AG, Switzerland) gave clear positive reactions, putting the overall infection rate of the orchard at 6.25%, while a second nearby orchard was found infected at a rate of 0.8%. The presence of PPV was confirmed by polymerase chain reaction (PCR) amplification using either the P1-P2 polyvalent primer pair or the P3M-P4b primer pair, which allows the specific amplification of isolates of the Rec and M strains (1). Sequencing of the 467-nt-long P3M-P4b PCR product (Genbank Accession No. KM035763), which spans the end of the NIb gene and the N-terminal hypervariable end of the coat protein gene, provided clear identification of the PPV isolate as belonging to the Rec strain, since it contained all the PPV-Rec specific mutations in the amplified region and showed 98.7 to 97.7% identity with a range of PPV Rec isolates mostly originating from the Balkans. Identification as a PPV-Rec isolate was also confirmed using a strain-specific reverse-transcription-PCR assay (3). This is, to our knowledge, the first report of the presence of PPV-Rec in France. This finding is worrisome given that PPV-Rec is considered well adapted to plum (2), the most important Prunus crop in Alsace. Further surveillance in Alsace during 2014 failed to provide evidence for the presence of PPV-Rec in other areas of the region away from the initial infection focus, which is currently undergoing eradication efforts. References: (1) T. Candresse et al. Phytopathology 88:198, 1998. (2) J. A. García et al. Mol. Plant Pathol. 15:226, 2014. (3) Z. Subr et al. Acta Virol. 48:173, 2004.