Rhizoctonia Solani as a Parasite of Fungi

Abstract

Rhizoctonia solani Kühn, an important soil-inhabiting parasite of cultivated plants, also parasitizes fungi. Except for Ambylosporium botrytis of the Fungi Imperfecti, only species of Phycomycetes were parasitized. R. solani attacks fungi by penetrating their aerial hyphae and establishing an internal parasitic mycelium or by coiling around their aerial hyphae or by a combination of both. The host-parasite relations are described. Evidence is presented that R. solani does not secrete an antibiotic effective in killing fungi at a distance. The hypothesis is presented that the host fungus and R. solani produce complementary chemical stimuli responsible for the development of parasitic hyphal coils and infection hyphae. Isolates of R. solani differ in virulence from highly virulent to avirulent. Four physiologic races were recognized on the basis of differential pathogenicity to Pythium debaryanum and Rhisopus sp. The effects of nutrition, temperature, light and other fungi on parasitism are given. The results of these studies indicate that good growth of the host and parasite was prerequisite for parasitism. Two isolates of R. solani produced basidiospores in culture. This is believed to be the first report of a basidiomycete parasitizing fungi belonging to the Phycomycetes and Fungi Imperfecti.