• Korean Journal Plant Pathology
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• v.3 no.3
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• pp.217-222
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• 1987

Pathogenicity of nine Rhizoctonia solani isolates of different anastomosis groups (AG) on seed and hypocotyls of red pepper, cucumber, Chinese cabbage and radish varied considerably from nonvirulent to highly virulent. Rhizoctonia solani AG 1 was highly virulent on the above four plant species. AG 2 type 1 was highly virulent on radish and Chinese cabbage, moderately virulent on red pepper, and AG 2 type 2 was avirulent or weakly virulent except red pepper. R. solani AG 5 was moderately virulent on hosts tested. In general, virulence of the R. solani isolates to a given host varied among anastomosis groups, but not within anastomosis groups. Anastomosis groups lacked host specificity. The pathogenicity was stronger in steam-sterilized soil than in non-sterilized field soil, if the inoculated plants were closely related with orginal host from which the pathogen was isolated. On the other hand, pathogen was more virulent in non-sterilized field soil than in steam-sterilized soil, if the inoculated ones were not closely related. Generally, contrary to other soil-brone plant pathogenic fungi, Rhizoctonia isolates tended to be more virulent in non-sterilized field soil than in the same soil which had been steamed. A potential danger of building up propagules of R. solani in southern horticultural area are discussed in terms of cropping system.