CHARACTERIZATION OF POPULATIONS OF RHIZOCTONIA-SOLANI AG-3 FROM POTATO AND TOBACCO

Historically, Rhizoctonia solani anastomosis group 3 (AG-3) was regard ed, as host specific, composed of isolates causing black scurf of pota to. Recently, isolates of R. solani AG-3 were reported causing target spot of tobacco in South Africa. In the United States, isolates causin g target spot of tobacco were identified as AG-2-2. Our anastomosis te sts indicated that isolates of R. solani from diseased tobacco in Nort h 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 ana lyses based on cellular fatty acids indicated that AG-3 isolates from tobacco were distinct from AG-3 isolates from potato. Isolates from to bacco had uniform cultural appearance, whereas isolates from potato sh owed cultural variation. Isolates of R. solani from potato were not pa thogenic on tobacco plants, and isolates from tobacco were not pathoge nic on potato plants.