Rhizoctonia damping off

The causative agent of the disease is the soil-borne fungus Thanatephorus cucumeris (anamorph Rhizoctonia solani). This pathogen is widely distributed and thrives as a saprophyte on decaying plant debris, but under favorable conditions, it colonizes the roots and stems of living plants, causing significant tissue necrosis.

This fungus has a very broad host range, affecting many vegetable, cereal, and pulse crops. Notably, it causes severe damage to alfalfa (Medicago sativa), where it manifests as crown and root rot. In alfalfa fields, the infection often leads to thinning stands and reduced forage productivity over time.

Symptoms typically start as water-soaked lesions that turn reddish-brown on the roots and hypocotyls of young seedlings. As the disease progresses, the stem tissue weakens, causing the seedlings to collapse—a classic case of damping off. In older plants, decay of the taproot and secondary roots leads to stunting and yellowing of the foliage.

Disease development is favored by warm, moist soil conditions and poor drainage. The pathogen survives in the soil for several years through sclerotia (hardened mycelial structures), which are highly resistant to environmental stress and allow the fungus to persist even in the absence of a susceptible host plant.

Control measures rely heavily on integrated pest management. Key strategies include improving soil drainage, utilizing crop rotations with non-host species, and treating seeds with appropriate fungicides. Maintaining optimal plant vigor through balanced fertilization and avoiding deep planting can significantly reduce the incidence of Rhizoctonia infections.