Rhizoctonia rot

Hypochnus solani (also known as Rhizoctonia solani) is a devastating soil-borne fungus categorized within the Basidiomycetes. As a versatile necrotrophic pathogen, it colonizes the roots, stems, and tubers of numerous host plants. It is widely recognized as the primary agent of the disease complex commonly referred to as Rhizoctonia disease or black scurf, which affects potato production globally.

The fungus manifests itself through various symptoms depending on the host and environmental stage. On potatoes, the most characteristic sign is the presence of black, hardened sclerotia on the tuber skin, often resembling soil particles. Additionally, it causes "stem canker," where the underground parts of the stem develop sunken brown lesions, leading to poor crop emergence and plant stunting.

The lifecycle of this pathogen centers on the sclerotia, which act as survival structures in the soil or on infected tubers. Under moist conditions, these sclerotia germinate to produce vegetative mycelium. The mycelium grows through the soil towards host tissues, where it secretes enzymes that break down plant cell walls, allowing the fungus to invade and kill host cells effectively.

Environmental conditions play a critical role in the severity of Hypochnus solani outbreaks. The pathogen thrives in relatively cool, moist soils, especially during the early stages of plant development. When soil temperatures remain below 18°C during planting, the host plant's growth slows down, providing a prolonged window of vulnerability for the fungus to infect sensitive tissues.

Effective management of this disease requires a combination of integrated pest management (IPM) practices. Key strategies include: sourcing certified disease-free seed tubers, applying targeted seed treatment fungicides, optimizing soil drainage to reduce excess moisture, and implementing long-term crop rotations with non-host species to reduce the overall inoculum density of the fungus in the soil.