Variation in virulence to dry beans, soybeans and maize among isolates of Rhizoctonia solani from beans

The relative susceptibility of dry beans ( Phaseolus vulgaris ), soybeans and maize to anastomosis group 4 isolates of Rhizoctonia solani was determined in greenhouse experiments. Large variations in virulence were found among 30 field isolates. This variation was not due to differential reductions in isolate virulence during axenic culture. There was considerable variation among isolates from within the same field but variability within isolates was small. Twelve of 30 isolates of R. solani were highly virulent to dry beans and soybeans, while the others were of low virulence. Soybeans were more susceptible than dry beans to both pre-emergence mortality and hypocotyl disease. No isolates were highly virulent to maize. The importance of using isolates with a high level of virulence for testing soybean cultivars for resistance to Rhizoctonia disease is stressed.