Differential Medium for Identification of Rhizoctonia solani AG-3. C. Castro, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. J. R. Davis, and M. V. Wiese, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. Plant Dis. 67:1069-1071. Accepted for publication 7 April 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1069.

Anastomosis groups (AG) of Rhizoctonia solani may coinhabit soil and differ in pathogenicity and epidemiology characteristics. Therefore, methods for rapid identification and separation of AG-types would be desirable. Separation of Rhizoctonia solani AG-3 from other Rhizoctonia AG-types was studied on Stewart’s medium and on potato-dextrose agar (PDA). One hundred twenty-six isolates of R. solani, representing AG-1, AG-2, AG-3, and AG-4 and four isolates of R. solani-like fungi were grown on these media. After incubation on Stewart’s medium, all AG-3 isolates were consistently and uniformly brown, whereas all other isolates were white. On PDA or other common media, the colony appearance of AG-3 isolates was less characteristic. Stewart’s medium might be a useful and rapid tool for differentiating isolates of R. solani AG-3.