[Molecular properties of potato spindle tuber viroid (PSTVd) isolates from the collection of the Russian Research Institute of Phytopathology].

The complete nucleotide sequences of more than 100 isolates of PSTVd collected from locations in the territory of Russia and the former USSR have been determined. These sequences represent 42 individual sequence variants, each containing 1-10 mutations with respect to the "intermediate" or type strain of PSTVd (GenBank Acc. No. v01465). Isolates containing 2-5 mutations were the most common, and 24 sequence variants are described here for the first time. Twenty one isolates contained a mutation found only in Russian and Ukrainian isolates of PSTVd up till now; i.e., replacement of the adenine at position 121 with cytosine (A121C). Many of these isolates contained two mutations--deletion of one of the three adenine residues occupying positions 118-120 plus replacement of the adenine at position 121 with either uracil or cytosine (A120, A121U/C). Both combinations of mutations were phenotypically neutral, i.e. symptom expression in Rutgers tomato was unaffected. Phylogenetic analysis of the sequences of different PSTVd isolates presented in work together with sequences of other naturally-occurring isolates obtained from Internet databases suggesting that known PSTVd isolates may be divided into four groups: i) a group of isolates from potato, tomato and solanaceous ornamentals where the type strain of PSTVd (PSTVd.018) may be considered to represent the ancestral sequence, ii) a group of isolates from potato, tomato and solanaceous ornamentals where PSTVd.123 play the same role as PSTVd.018 for the first group, and iii) a group of potato isolates where PSTVd.125 is a possible ancestral sequence. The fourth and most divergent group of PSTVd isolates differs significantly from these first three groups. The majority of isolates in this group originate from New Zealand and Australia and infect different solanaceous hosts (tomato, pepper, cape gooseberry, potato, and others).

Russian isolates of potato spindle tuber viroid.

Forty PSTVd isolates collected from five regions of Russia (North-western, Central, Volga region, Northern Caucasus and the Far East) were sequenced during 2006-2008. All isolates lacked the adenine residue present at position 123 of the type strain; i.e., PSTVd-intermediate (GenBank V01465). Nineteen Russian isolates also contained an adenosine --> cytosine substitution at position 120. Twenty two additional unique changes were also observed in one or more of the isolates sequenced.

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.