There are many diseases that affect agricultural produce, and many fungal agents that cause diseases in plants. We shall discuss one such common fungal pathogen―Rhizoctonia solani, in this article.
What is Rhizoctonia solani?
This is a soil fungus that infects plants. It causes various plant-related diseases, like collar rot, root rot, wire stem, and damping off. The infection is seen in seedlings, and proves to be fatal in most cases. Damping off is the most common seedling problems, caused by the fungus that leads to death of the seedling. Cabbage, cauliflower, and plants of the same family are commonly affected by wire stem, a disease that leads to production of a wiry stem.
Rhizoctonia solani has multinucleated hyphal cells. This fungal pathogen does not produce any asexual spores, that are called conidia. It may, however, produce sexual spores called basidiospores occasionally on infected plants. It is asexual, and it is mostly found as vegetative mycelium. It produces white mycelium that appears as small treads around the plants. So basically, it has a cross wall within the hyphae, called dolipore septum. The branches of the mycelium are produced at right angles. When a plant is invaded by this pathogen, there are sexual spores produced. These sexual spores are produced on structures called a basidia. Each basidium produces four spores. When there is moisture in the environment, the basidiospores disperse and germinate. There is one nucleus in every basidiospore. When the germinating spores produce hyphae, spores fuse forming new hypae, with an influx of different nuclei types.
It infects many plants, like beans, alfalfa, soybean, lime bean, cucumber, peanut, papaya, corn, eggplant, cabbage, cauliflower, etc. This fungal infection is found to have more than 500 hosts in the United States. When it infects a germinating bean seed or seedling, one can observe red spots. These red spots tend to appear sunken, and as they expand, they kill the plant. Younger plants tend to show reddish-brown to brown collar rots. This causes stunted growth and decrease in plant vitality. The collar area may thicken and also develop callus formation. Root rot causes plant death and reduction in the yield. In periods of high moisture, one may observe leaf and pod rots. The fungal threads called the web blights tend to cover the leaves and pods entirely.
Control is very important, as this fungal pathogen affects young plants. Thus, it causes widespread damage and decrease in yield. This fungus can survive in the soil for many years, as it has the ability to infect a wide number of different hosts. It tends to produce irregular-shaped brown or black structures called sclerotia in the soil as well as plant tissue. This helps the plant survive for many years. Control is carried out by removing and burning the infected plants. One should avoid using the infected plant material as compost, as the spores tend to survive. Thus, it is important to destroy the infected plant immediately. There are many fungicides available that help control this fungus. Soil fumigation and soil sterilization will ensure that the fungus is removed from the soil. In some cases, farmers tend to skip several planting cycles. This helps in reduction of nutrition and death of fungus.
This fungal pathogen causes a lot of damage to plants and crops. If one observes infection on even a single plant, it is important to destroy it and take control measures. After the harvest, it is important to remove all debris, as it will help in reduction of soil inoculum. An alternative method to reduce the number of fungal spores within the soil is through plantation of a non-susceptible host.