1978 Volume 44 Issue 5 Pages 554-560
In plastic house cropping of spinach having its growing season from May to October, damping-off and foot rot diseases caused by Rhizoctonia solani Kühn were most serious from June to Septmeber. The occurrence of the fungus was more frequent at the earlier growth stage of the plant. The fungus was more dominant in the plastic house cropping in drained rice paddy fields than in upland fields or in open field cropping, and was less frequent in light clay soil than in clay loam or in loam soil. Isolates of R. solani from spinach were assigned to 5 anastomosis groups (AG). Isolates occurred most frequently and being most pathogenic to spinach seedlings were of AG-4, followed by ones of AG-2, type-2. The former group was most dominant at the earlier growth stage of the plant irrespective of the growing season, cropping histories of the plant and soil types of the fields. The latter group was frequently isolated from drained rice paddy fields and increased with the development of the plant. The groups, AG-1, AG-2, type-1 and AG-1 were additional ones which were found less frequently in plastic house cropping.