Rhizoctonia Solani - Hosts and Symptoms

Hosts and Symptoms

Rhizoctonia solani primarily attacks seeds of plants below the soil surface, but can also infect pods, roots, leaves and stems. The most common symptom of Rhizoctonia is "damping off", or the failure of infected seeds to germinate. Rhizoctonia solani may invade the seed before it has germinated to cause this pre-emergent damping off, or it can kill very young seedlings soon after they emerge from the soil. Seeds that do germinate before being killed by the fungus have reddish-brown lesions and cankers on stems and roots.

There are various environmental conditions that put the plant at higher risk of infection due to Rhizoctonia, the pathogen prefers warmer wet climates for infection and growth. Post-emergent damping off is a further delay in attack of Rhizoctonia solani. The seedling is most susceptible to disease in its juvenile stage.

Cereals in regions of England, South Australia, Canada, and India experience losses caused by Rhizoctonia solani every year. Roots are killed back, causing plants to be stunted and spindly. Other non cereal plants in those regions can experience brown stumps as another symptom of the pathogen. In England, this is called purple patch. Rhizoctonia solani can also cause hypocotyl and stem cankers on mature plants of tomatoes, potatoes and cabbage. Strands of mycelium and sometimes sclerotia appear on their surfaces. Roots will turn brown and die after a period of time. The best known symptom of Rhizoctonia solani is black scurf on potato tubers which are the sclerotia of the fungus.

The fungus has a wide host range. Strains of Rhizoctonia solani may differ in the hosts they are able to infect, the virulence of infection, selectivity for a given host ranges from non-pathogenic to highly virulent, the temperature at which infection occurs, the ability to develop in lower soil levels, the ability to form sclerotia, the growth rate, the survival in a certain area. These factors may or may not show up given the environment and host that Rhizoctonia attacks.