Studies on Rhizoctonia solani Kuhn, the cause of the black scurf disease of potato

Following a discussion of the nomenclature of R. (Corticium) solani, 15 isolates from potato were divided into 3 groups on cultural characters. Growth was not suppressed by the incorporation of oxytetracycline or streptomycin in the media. None of the isolates was very pathogenic; the majority induced light to moderate infection and showed no correlation between type of isolate and pathogenicity.

The fungus was isolated from soil by inserting pieces of jute stem fixed on steel entomological pins for easy recovery. C. solani could be recovered after only 12 h, and was isolated on either cherry agar or water agar. On cherry agar 49 morphologically distinct types were recognized from naturally infected soil. The pathogen withstood severe winter conditions and persisted in soil for at least 9 months. No correlation was observed between degree of pathogenicity in potato and on other hosts.