Anastomosis groups and sensitivity to fungicides of Rhizoctonia solani strains isolated from potato in Russia

A survey of Rhizoctonia solani isolates from potato tubers and stems grown in European and Far Eastern regions of Russia in 2012–2020 was conducted. Ten isolates from German and two from Australian seed potato tubers were analyzed, too. Species-specific region ITS1/2 of rDNA was sequenced and analyzed for all 53 isolates. Out of those, 51 isolates were classified as multinucleate and two as binucleate Rhizoctonia. Among the tested multinucleate isolates, 49 belong to AG 3PT, the most frequent group on potato, and two isolates to AG 5 group. Binucleate Rhizoctonia were determined as AG K. All AG 5 and AG K isolates were isolated from Russian potato tubers (AG 5) and stems (AG K). A study of fungicide resistance showed that all tested isolates were susceptible to thiabendazole (EC50 < 7.2 mg/l) and fludioxonil (EC50 < 42 mg/l). Resistance to benzoic acid varied between isolates, and EC50 ranged from 5.38 to 362 mg/l. After long-term (1 month and more) cultivation on Petri dishes with fludioxonil, several strains developed resistant sectors. Almost all strains were sensitive to pencycuron (EC50 < 5 mg/l), while three isolates with very high resistance (EC50 > 1000 mg/l) were detected. Two resistant isolates belonged to the anastomotic group AG 5 and one to AG 3. To our knowledge, this is the first report of pencycuron-resistant R. solani strains in Russia. Three resistant to pencycuron multinucleate and binucleate isolates grow at temperature + 34 °C. After a week of incubation, no growth of sensitive multinucleate isolates at + 34 °C was registered. © 2021, Deutsche Phytomedizinische Gesellschaft.