Diversity and pathogenicity of anastomosis groups of Rhizoctonia associated with potato stem canker and black scurf diseases in Brazil

Abstract

Sixty-seven isolates of Rhizoctonia obtained from potato stems and tubers in the main potato growing regions of Brazil between 2013 and 2014 were analyzed for their molecular and pathogenicity characteristics. Using phylogenetic analysis of the internal transcribed spacer region of ribosomal DNA, 49 isolates were identified as R. solani and 18 isolates as binucleate Rhizoctonia (BNR). Twenty-five isolates (37.3%) belonged to anastomosis group (AG)-3 PT, 20 (29.9%) to AG-4 HGI, 15 (22.4%) to AG-R, three (4.5%) to AG-2-1, three (4.5%) to AG-A, and one (1.5%) to AG-1 IB. Most of the AG-3 PT, AG-4 HGI, AG-A and AG-R isolates, and all isolates of AG-2-1 and AG-1 IB were obtained from tubers with black scurf symptoms. AG-4 HGI isolates were widely distributed and recovered from six out of seven Brazilian states, including 11 potato-growing fields. All isolates were pathogenic to potato, causing necrotic lesions on subterraneous stems, but there were differences in aggressiveness among different AGs. AG-4 HGI was significantly more aggressive to potato plants than other AGs. To our knowledge, this is the first detailed report of the AG composition of Rhizoctonia populations causing potato diseases in different Brazilian regions.