LAUSR

To investigate the current status of viroid infection in potato fields in Russia, potato spindle tuber viroid (PSTVd) and chrysanthemum stunt viroid (CSVd) were detected in potato (Solanum tuberosum) and S. nigrum plants growing in the Volga (V), North-Western (NW), and Far Eastern (FE) federal districts in Russia. While both PSTVd and CSVd were detected in potato samples from the V and FE regions, only CSVd was detected in potato samples from NW. CSVd was detected in S. nigrum from FE, and this was the first detection of CSVd in S. nigrum. Analysis of the complete genomes of 30 PSTVd and 10 CSVd variants revealed that 5 and 7 PSTVd variants from V and FE, respectively, and 2, 4, and 3 CSVd variants from V, NW, and FE, respectively, were new. Analysis of the infectivity of and symptoms caused by 15 Russian PSTVd isolates in tomato revealed that 14 PSTVd isolates caused intermediate or severe symptoms, and only FP14 caused mild symptoms. Our survey revealed that most of the Russian PSTVd isolates from V and FE caused intermediate symptoms in tomato, and the genome sequences were identical to that of PSTVd isolated from S. demissum. Phylogenetic analysis of nucleotide sequences of the Russian PSTVd variants showed their close relationship to previously studied PSTVd isolates, suggesting that most strains in Russia have not substantially changed genetically, but have widely spread in potato fields.