Genetic diversity of phytoplasmas identified in peach (Prunus persica) accessions at the Canadian Clonal Genebank.

Peach [Prunus persica (L.) Bastch] is mainly cultivated in Canada in Ontario province (82% of national production). A variety of symptoms typical of a phytoplasma infection were observed some of the 83 P. persica accessions during June-August 2009 at the Canadian Clonal Genebank. PRU0430 (‘HW274’, from Canada), PRU0380 (‘GF305’ from France), PRU0334 (‘RedSkin’ from USA), PRU0155 (‘Harblaze’, from Canada) and PRU0375 (‘Babygold #5’, from USA) showed decline, leaf reddening, yellowing, shortening of internodes, witches’ broom and reduced fruit size; while ‘PRU0382’ (peach-almond ‘Kando’ from the Czech Republic) and PRU0445 (peach ‘HW271’ from Canada) exhibited peach rosette-like symptoms. Leaf samples from symptomatic and symptomless plants were collected and total DNA was extracted. Phytoplasma universal 16S rRNA primers, R16mF2/R1 and R16F2n/R2 and fU5/rU3 were used in nested PCR assays. R16F2n/R2 nested PCR products were obtained for ‘PRU0430’, ‘PRU0380’, ‘PRU0155’, ‘PRU0334’ and ‘PRU0375’; while fU5/rU3 PCR products were obtained for ‘PRU0382’ and ‘PRU0445’. Plants lacking symptoms yielded no PCR products. Amplicons were purified, cloned, and sequenced. BLAST analysis showed that R16F2n/R2 sequences (GU223903) were 99% identical to 16S rRNA phytoplasma sequences for group 16SrVII ‘Candidatus Phytoplasma fraxini’, while those from fU5/rU3 amplicons (GU223904) shared 99% identity with those of group 16SrI ‘Candidatus Phytoplasma asteris’. AluI, RsaI and MseI RFLP analysis yielded profiles consistent with those of phytoplasma in subgroups 16SrVII-A and 16SrI-B, respectively. To our knowledge, this is the first report of a 16SrI-related phytoplasma in peach in Canada, and the first world report of a 16SrVII-related phytoplasma strain identified in peach after a case in southern Italy.