First Report of Plum pox virus Recombinant Strain on Prunus spp. in Canada

In July of 2008, during the Canadian Plum pox virus (PPV) eradication survey, three Prunus spp. trees (B-5, B-6, and C-1) in a home owner's yard in Grimsby, ON, Canada were found to be infected with PPV by triple antibody sandwich (TAS)-ELISA using the 5B generic monoclonal detecting antibody (1) and reverse transcription (RT)-PCR using the well-validated universal primer set P1/P2. All three trees were grafted on an unknown plum rootstock cultivar. Tree B-5 contained grafts of unknown peach (P. persica) and plum (P. domestica) cultivars, tree B-6 contained the same peach graft as tree B-5 and an unknown apricot (P. armeniaca) cultivar, and tree C-1 was grafted with the same plum cultivar as tree B-5. Strain typing was done by TAS-ELISA using strain-specific monoclonal antibodies for D, M, C, and EA strains. Positive results were obtained with the M-specific test. Strain typing by RT-PCR also was done using primers specific for D, M, W, and recombinant (Rec) strains. Positive results were obtained with the M and Rec primers (4). The 605-bp fragment generated by the PPV Rec primers, which spans the recombination site, was cloned and sequenced. The nucleotide sequences obtained from B-5, B-6, and C-1 are 99% identical to each other and approximately 98 and 99% identical to the PPV Rec isolates BOR-3 and J4c, respectively. Correspondingly, percentage identities are approximately 90% for PPV M, 84% for PPV isolate D-Fan (a typical Canadian D isolate), and 69% for PPV W. The deduced amino acid sequence of B-5, B-6, and C-1 are 98 to 99% identical to each other, 99% identical to the PPV Rec isolates BOR-3 and J4c, 92% identical to isolates of PPV M, and only 84% identical to the typical Canadian D isolate PPV Fan. The P3-6K₁ genomic region was amplified using primers that generate a 836-bp fragment (2). This region was 97 to 98% identical to the PPV Rec isolates BOR-3 and J4c, 96 to 97% identical to isolates of PPV D, but only 86% identical to isolates of PPV M. The data above confirm that the PPV isolates B-5, B-6, and C-1 belong to the strain PPV Rec (3). To our knowledge, this is the first report of PPV Rec in North America, and together with PPV D and W, it represents the third PPV strain found on this continent. An intensive survey of all Prunus spp. within a 1.5-km radius area surrounding the home owner's property failed to reveal any additional PPV-positive plants. The three positive plants were removed. References: (1) M. Cambra et al. EPPO Bull. 24:569, 1994. (2) M. Glasa et al. Arch. Virol. 147:563, 2002. (3) M. Glasa et al. J. Gen. Virol. 85:2671, 2004. (4) A. Šubr et al. Acta Virol. 48:173, 2004.