Rhizoctonia solani

Systematic position and pathogen type: Rhizoctonia solani (teleomorph Thanatephorus cucumeris) belongs to the kingdom Fungi, phylum Basidiomycota. It is a soil-borne necrotrophic fungus known for its wide host range, affecting hundreds of plant species. The pathogen does not produce asexual spores but spreads primarily through mycelium and highly resistant sclerotia in the soil.

Diseases and host crops: This pathogen is responsible for various plant diseases, most notably black scurf of potatoes, root and crown rots in cereal crops, damping-off in seedlings of vegetables, and stem cankers in beans and sugar beets. Its broad host range makes it a consistent threat across various agricultural sectors.

Biology and life cycle: The fungus survives as sclerotia or mycelium in soil and on organic debris. Infection occurs when hyphae penetrate the plant tissues, often facilitated by moisture and temperature levels. The pathogen exhibits significant saprophytic ability, allowing it to maintain populations in the absence of a host crop, which complicates management efforts significantly.

Conditions and pathogenicity: Rhizoctonia solani thrives in cool to moderate temperatures (15–22°C) and moist soil conditions. The pathogenicity is highest during the early seedling stage, causing significant pre-emergence and post-emergence damping-off. In established plants, it damages the root cortex and stem base, significantly reducing plant vigor and yield quality.

Management and control: Managing this pathogen requires an integrated approach to limit soil inoculum levels and prevent early infection.

• Use of pathogen-free seeds and certified seed potatoes.
• Crop rotation to reduce the build-up of sclerotia in the soil.
• Chemical seed treatment with effective fungicides.
• Soil moisture management and maintenance of proper drainage.
• Application of beneficial microbial agents like Trichoderma species.