Abstract
The presence of Rhizoctonia spp. was investigated by isolation from soil and plants in natural grasslands, and the seasonal development was compared. Isolated Rhizoctonia spp. belonged to the R. solani anastomosis groups (AG)-2-2 or AG-6, binucleate Rhizoctonia spp. (BnR) AG-A, AG-B or AG-Ba and R. oryzae type. Rhizoctonia spp., except for the R. orvzae type, were isolated from the upper layers of soil in applying the bait method. Frequency of Rhizoctonia spp. in relation to seasonal development was relatively stable from June to September but decreased in October. Rhizoctonia spp. from plants could be isolated with a higher frequency from the roots of Pleioblastus variegatus var. viridis in July, and from Rosa multiflora and Lespedeza bicolor var. japonica in June, September and October. These Rhizoctonia spp. isolated by the bait method belonged mainly to the BnR AG-B group and R. oryzae type, and those from plant debris and root of plants belonged mostly to the BnR AG-A group. Especially, R. solani AG-2-2 causing root rot of Japanese radish could be isolated from plant debris and the roots of L. bicolor var. japonica and R. multiflora. Thus, it is suggested that the ecology of Rhizoctonia spp. in the soil of natural grasslands varies with the groups. It was also shown that R. solani AG-2-2 occurs as a saprophyte on the roots of plants and plant debris.
