Assessment of diversity of plant species affected by phytoplasma of X-disease (16SR-III) group in Russia

Worldwide, there is an increase in the harmfulness of plant diseases transmitted by insects, including phytoplasmas. In Russia, phytoplasma diseases have been studied insufficiently. The aim of the study was to monitor phytoplasma diseases in various economic regions of the Russian Federation and determine the taxonomic affiliation of their pathogens. The task of the study was to identify the species composition of plants affected by phytoplasmas belonging to the 16Sr-III group and their potential vectors. Molecular genetic studies were carried out at the All-Russian Research Institute of Phytopathology (VNIIF) in 2006-2021. Plants with symptoms of phytoplasma infection and leafhoppers collected in the Moscow and Samara regions were the material of the research. The presence of phytoplasma DNA in the samples was determined using sequentially direct and nested PCR with the primer pairs: P1/16S-SR and R16F2n/R16R2, respectively. Phytoplasmas were identified by analyzing restriction fragment length polymorphism (RFLP) after treatment of 1.2 Kb DNA amplicons with restriction endonucleases. In a quarter of the analyzed potato samples and five of the eight surveyed economic regions (Volga, North Caucasian, Ural, Central and West Siberian), phytoplasma of the 16SrIII group was found. Among other solanaseous, phytoplasma of the 16SrIII group was found in pepper and garden petunia, as well as in two species of wild potatoes. In total, the phytoplasma of X-disease was detected in 51 species of plants from 19 families, including Fabaceae (12 species), Asteraceae (10), Rosaceae (6), and Solanaceae (5). In other families, 1–2 plant species infected with this phytoplasma were identified. The phytoplasma of the 16SrIII-B subgroup was most frequently found in plant material. Phytoplasma of the 16SrIII-F subgroup was detected in two plant species: astilbe (Astilbe thunbergii (Siebold & Zucc.) Miq.) and hybrid clover (Trifolium hybridum L.). In potential vectors (leafhoppers Euscelis incisа Kirschbaum, Sonronius binotatus Sahlberg, Macrosteles laevis Rib. and Psammotettix striatus L.), phytoplasma of the 16SrIII group, including the 16SrIII-O and 16SrIII-P subgroups, was found.