Molecular characterization of phytoplasmas identified in Prunus species at the Canadian Clonal Genebank.

In Canada, more than 3,600 hectares (8,900 acres) are devoted to peach, nectarine and apricot cultivation with most production occurring in the provinces of Ontario and British Colombia. The farm gate value of peach, nectarine and apricot in Canada was more than $ 40 million in 2008. More than 90 accessions of peach, nectarine and apricot are represented at the Canadian Clonal Genebank (CCG). ‘Candidatus Phytoplasma asteris’ (16SrI) and ‘Ca. Phytoplasma fraxini’ (16SrVII), have been recently identified affecting peach, Prunus persica (L.) Bastch, at the CCG, in a collection established in the field more than 15 years ago, and were partially characterized based on analysis of the 16S rDNA. In an extensive survey leaf samples from symptomatic and symptomless plants of all plants of the CCG were collected and total DNA was extracted. Phytoplasma universal 16S rRNA primers were used for direct amplification followed by internal primers in nested PCR assays. PCR products were obtained for samples only from 7 symptomatic plants. Plants lacking symptoms yielded no PCR products. The identified phytoplasmas were then further analyzed with multi-gene sequences (multiple phylogenetic markers) technique that currently provide a basis to better distinguish phytoplasma species or strains, characterize phytoplasma populations and define epidemiology and ecology further PCR assays followed by restriction fragment length polymorphism (RFLP) analyses and/or sequencing of ribosomal protein l22, and tuf genes were carried out on the 16SrI and 16SrVII phytoplasma strains identified at the CCG. The accessions held at the CCG provide a unique research opportunity to assess phytoplasma occurrence and expression across a wide spectrum of Prunus genotypes. These studies may result in the identification of potential sources of resistance to these pathogens.