Rhizoctonia Solani - Disease Cycle

Disease Cycle

Rhizoctonia solani can survive in the soil for many years in the form of sclerotia. Sclerotia of Rhizoctonia have thick outer layers to allow for survival, and they function as the overwintering structure for the pathogen. In some rare cases(such as the teleomorph) the pathogen may also take on the form of mycelium that reside in the soil as well. The fungus is attracted to the plant by chemical stimuli released by a growing plant and/or decomposing plant residue. The process of penetration of a host can be accomplished in a number of ways. Entry can occur through direct penetration of the plant cuticle/epidermis or by means of natural openings in the plant. Hyphae will come in contact with the plant and attach to the plant by which through growth they begin to produce an appressorium which penetrates the plant cell and allows for the pathogen to obtain nutrients from the plant cell. The pathogen can also release enzymes that break down plant cell walls, and continues to colonize and grow inside dead tissue. This breakdown of the cell walls and colonization of the pathogen within the host is what forms the sclerotia. New innoculum is produced on or within the host tissue, and a new cycle is repeated when new plants become available. The disease cycle begins as such- 1)the sclerotia/mycelium overwinter in plant debris, soil or host plants. 2)The young hyphae and fruiting basidia(rare) emerge and produce mycelium and rarely basidiospores. 3)The very rare production of the germinating basidiospore penetrate the stoma whereas the mycelium land on the plant surface and secrete the necessary enzymes onto the plant surface in order to initiate invasion of the host plant. 4)After they mycelium successfully invade the host- necrosis and sclerotia form in and around the infected tissue which then leads to the various symptoms associated with the disease such as soil rot, stem rot, damping off etc. and the process begins all over again.