Isolates of Rhizoctonia solani Anastomosis Group 2-2 Pathogenic to Soybean. Zonglin Liu, Postdoctoral Research Associate, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana 61801-4709. J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign (UIUC), 1102 S. Goodwin Avenue, Urbana 61801-4709. Plant Dis. 75:682-687. Accepted for publication 14 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0682.

Two highly virulent isolates of Rhizoctonia solani, 61D-3 and 65L-2 (ATCC 66489), from diseased soybean (Glycine max) plants grown in Illinois were identified as members of anastomosis group (AG) 2-2. They caused crown and root rot on inoculated plant species in the Chenopodiaceae, Fabaceae, and Poaceae at an inoculum level of 100 μg of fresh mycelium per gram of soil in the greenhouse. Both isolates produced few loose, thick-walled sclerotia and maintained their pathogenicity to soybean after 2 yr in storage. The minimum, optimum, and maximum growth temperatures for both isolates were 8, 30, and 40 C, respectively. Single hyphal cells of isolate 65L-2 from fragmented mycelium germinated directly, similar to spores of other fungi. A previously undescribed gobletlike structure developed before a viable germ tube was formed. The number of nuclei per cell varied. Both isolates were thiamine auxotrophic. They differed from most sugar beet isolates at loci aco, est-1, est-2, and pgm as determined by isozyme analysis.