Identification of phytoplasma species associated with potato diseases in Russia

Four out of six known potato diseases attributed to phytoplasma infection were previously reported to occur in Russia based on a combination of biological properties such as symptomatology and/or vector relationships and electron microscopy of infected phloem tissue. In 2007, the first molecular identification of potato diseases causing symptoms including purple top, round leaves, stunting, bud proliferation and formation of aerial tubers was carried out using PCR methods. A nested PCR using primer pair P1/P7 in the first amplification followed by R16F2n/R16R2n in the second amplification was performed to detect phytoplasma in infected potato samples. PCR products were digested singly with several restriction enzymes. Comparison of RFLP profiles with published profiles was used for identification of the putative phytoplasma detected. The majority of 49 PCR positive potato samples showed RFLP profiles of 16S rDNA sequences very similar or identical to stolbur phytoplasma, a strain belonging to stolbur phytoplasma group (16Sr XII), subgroup 16SrXII-A, and only two showed RFLP profiles similar to those of aster yellow phytoplasma strains ('Candidatus Phytoplasma asteris') belonging to aster yellows phytoplasma group (16SrI), subgroup 16SrI-A and 16SrI-B. The results demonstrated that stolbur phytoplasma is prevalent in several potato growing regions of Russia.