Diversity and pathogenicity of anastomosis groups of Rhizoctonia associated with brassicas in Brazil

Abstract

Seventy-eight Rhizoctonia isolates were obtained from brassicas in five Brazilian states between 2015 and 2017. The isolates were identified by phylogenetic analysis of the rDNA internal transcribed spacer region (ITS) and tested for pathogenicity and aggressiveness. Sixty-eight isolates were identified as R. solani and 10 isolates as binucleate Rhizoctonia. The most prevalent anastomosis group (AG) was AG-4 HG-I (83.3% of isolates), followed by AG-A (7.7%), AG-1 IB (2.6%), AG-G (2.6%), AG-R (2.6%) and AG-2-2 IIIB (1.3%). AG-4 HG-I isolates were widely distributed and recovered from all Brazilian states sampled, including 12 brassicas-growing fields. All isolates were pathogenic to broccoli, cauliflower and kale, causing necrotic lesions on subterraneous stems. There was no significant difference in aggressiveness among the different AGs in broccoli, but AG-1 IB isolates were more aggressive to cauliflower and AG-4 HG-I isolates were more aggressive to kale. This study is the first report of AG-4 HG-I, AG-2-2 IIIB, AG-A, AG-G and AG-R infecting brassica plants in Brazil. To our knowledge, this is the first detailed research of the AG composition of Rhizoctonia populations causing brassica diseases in Brazil.