Grouping of Rhizoctonia solani Kühn with Hyphal Anastomosis

Anastomosis phenomena among 234 isolates of Rhizoctonia solani (Thanatephorus cucumeris) indicated that 214 isolates fell into one of six groups (AG-1∼AG-6) and 20 isolates were not assigned any one of groups. In the course of hyphal contact there were three cases, a) hyphae of two isolates were attracted each other, b) hypha of one isolate was attracted by hypha of another isolate, and c) these attracting phenomena were not observed and fusion was left to chance.Anastomosis within one and the same isolate was perfect fusion. Anastomosis between isolates from the same group was imperfect or contact fusion. It was observed that the imperfect fusion resulted in the death of fused and adjacent cells. Most isolates fell into AG-1 were those from rice plant, sugar beet, and soils. Most isolates of AG-2 were from soils, flax, and Cruciferae. All isolates of AG-3 were from Solanaceae (mostly potatoes). The majority of isolates of AG-4 were from Leguminosae and sugar beet. The majority of iaolates of AG-5 were from soils. Most isolates of AG-6 were from sugar beet and soils to which sugar beets had been cultivated.It is suggested that there may be pathological and ecological differentiation in R. solani.