Stachybotrys elegans: a destructive mycoparasite of Rhizoctonia solani

Abstract

Stachybotrys elegans colonizes hyphae as well as sclerotia of Rhizoctonia solani. Germinability of sclerotia, which had been incubated with the mycoparasite for 49 d, decreased from 84% to 5% as compared with 86% germinability of untreated sclerotia. Light and electron microscopic observations revealed that S. elegans grew toward and coiled around the host cells. In pure culture, cells of S. elegans were surrounded by extracellular fibrillar material. The production of this material was enhanced during contact and colonization of host hyphae only. This fibrillar material was not observed during interaction of the mycoparasite with host sclerotial cells. Penetration of host cells was accomplished by either unspecialized hyphal branches or pseudoappressoria. Penetration of host cells and emergence from them by the mycoparasite is apparently accomplished by both mechanical and enzymatic activity. Trophic hyphae of the parasite developed within the host cytoplasm, resulting in granulation of the cytoplasm and ultimately death of host cells. Papillae of unknown origin and chemical composition were frequently detected in colonized sclerotial cells. The above results indicate that mycoparasitism is the mode of action by which S. elegans attacks its host.