Virulence of Isolates of Rhizoctonia solani AG-3 Collected from Potato Plant Organs and Soil

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Abstract
Isolates of Rhizoctonia solani were collected directly from hymenia and lesions on potato stems and sclerotia on tubers and by direct and indirect methods from soils. Isolates were collected soil planted to barley, bluegrass and carrot and from fallow soil. Nearly 95% of isolates from plants and tubers were determined to be members of anastomosis group 3 (AG-3), whereas only 52% of isolates from soil were AG-3. Most isolates of R. solani AG-3 were moderately to highly virulent on potato sprouts at 10 C. On average, isolates from hymenia were significantly more virulent than isolates from lesions, but neither was significantly different in virulence from isolates collected from sclerotia or soil. Crop, year, and growth rate of isolates at the time of collection also had no significant effect on relative virulence.