Characterization of Rhizoctonia species associated with common bean in Idaho

Between 2018 and 2020, 106 isolates of the Rhizoctonia species complex and a single isolate of Waitea zeae were isolated from the stems and roots of common bean plants (Phaseolus vulgaris) grown in Idaho. To determine the anastomosis group (AG) of each isolate, sequencing of the rDNA internal transcribed spacer region was conducted. The majority of isolates (65.5%) belonged to the multinucleate Rhizoctonia solani, while 34.6% were binucleate Rhizoctonia. The most frequently isolated AG subgroup was AG4 HG-II (28 isolates), followed by AG A (15 isolates), AG 4 HG-I (13 isolates), and AG K (13 isolates). Pathogenicity tests were conducted on bean seedlings with representative Idaho isolates to assess their aggressiveness. The results revealed a wide range of aggressiveness among the isolates. AG 4 HG-I was the most aggressive AG on stems, followed by an isolate of AG 1-IB and the AG 11. This study provides the first evidence of the relative AG composition of Rhizoctonia species populations causing disease in common bean crops in Idaho.