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Characterization of Populations of Rhizoctonia solani AG-3 from Potato and Tobacco. J. Stevens Johnk, Research assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108; R. K. Jones(2), H. D. Shew(3), and D. E. Carling(4). (2)Associate professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; (3)professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; (4)professor, Department of Plant Pathology, University of Alaska, Fairbanks 99645. Phytopathology 83:854-858. Accepted for publication 10 May 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-854.

Historically, Rhizoctonia solani anastomosis group 3 (AG-3) was regarded as host specific, composed of isolates causing black scurf of potato. Recently, isolates of R. solani AG-3 were reported causing target spot of tobacco in South Africa. In the United States, isolates causing target spot of tobacco were identified as AG-2-2. Our anastomosis tests indicated that isolates of R. solani from diseased tobacco in North Carolina belong to AG-3. Furthermore, the tobacco isolates, like AG-3 from potato, were prototrophic for thiamine, whereas isolates of AG-2-2 were auxotrophic for thiamine. Cluster and principal component analyses based on cellular fatty acids indicated that AG-3 isolates from tobacco were distinct from AG-3 isolates from potato. Isolates from tobacco had uniform cultural appearance, whereas isolates from potato showed cultural variation. Isolates of R. solani from potato were not pathogenic on tobacco plants, and isolates from tobacco were not pathogenic on potato plants.