Rhizoctonia solani

Rhizoctonia solani is a species of fungus that belongs to the order Cantharellales. This fungus is usually found in its simple, thread-like form.

This fungus is found all over the world. It can make many plants sick by causing diseases like root rot, damping off, and wire stem. Even so, Rhizoctonia solani can also help some plants, like orchids, by forming special partnerships called mycorrhizal associations that support the plants' growth.

Taxonomy

In 1858, a scientist named Julius Kühn found a fungus on sick potato tubers and named it Rhizoctonia solani, after the potato plant Solanum tuberosum.

Later, in 1956, another scientist named M.A. Donk gave it a different name, Thanatephorus cucumeris, for its spore-bearing form.

Researchers learned that Rhizoctonia solani is actually a group of related fungi. They studied the fungi by looking at their tiny threads, called hyphae. They found that these fungi could be divided into at least 25 different groups. Modern science, using DNA, supports this grouping. Today, Rhizoctonia solani includes both simple and complex forms of the fungus.

Hosts and symptoms

Rhizoctonia solani sensu lato causes many plant diseases. It can make grass look patchy, called brown patch. It can stop seeds from growing, known as damping off. It can create black spots on potatoes and cause rot in roots of crops like sugar beets and cucumbers. This fungus can infect many plants, and its behavior can change based on the strain.

Rhizoctonia solani mainly attacks seeds and young plants in the soil. One problem it causes is damping off, where seeds do not grow or seedlings die just after they appear. When it attacks parts of plants above the ground, it can create brown spots on leaves, stems, and roots. The fungus grows best in warm, wet conditions. It can make crops like cereals, tomatoes, potatoes, and cabbages weak and unhealthy.

Disease cycle

Rhizoctonia solani can live in the soil for many years as small, hard structures called sclerotia. These sclerotia help the fungus survive cold winters. The fungus is drawn to plants by special chemicals that plants give off.

The fungus can enter a plant in different ways. It might go through the plant's skin directly or use natural openings. Once inside, the fungus can break down the plant's cells and use them for food. This creates new sclerotia, and the cycle starts again when new plants grow. The disease can cause problems like rot in the soil, stems, or young plants.

Environment

This fungus grows best in warm, wet weather. Farmers often see sick plants when they harvest their crops in late summer. Things that help the fungus grow are having plants nearby, lots of rain or watering, and warm temperatures in spring and summer. Soil that does not drain well also helps the fungus. The fungus spreads through small, tough parts called sclerotia. These can move by wind, water, or when soil is moved from one place to another.

Identification

Basidiocarps (fruit bodies) of Rhizoctonia solani are thin and smooth, like a web. Under a microscope, they have wide hyphae without special parts called clamp connections. The fungus can also grow in a form called anamorphs, which includes hyphae and small structures called sclerotia. In a lab, the fungus makes white to brown threads called mycelium, and its hyphae often form chains and branch at right angles.

Management

Controlling Rhizoctonia solani can be hard, but there are ways to make it less harmful. Farmers can rotate crops, plant in warmer soil, and choose resistant varieties to help plants stay safe. Keeping soil well-drained and avoiding wet areas can also help.

Some chemicals, like pentachloronitrobenzene (PCNB), can help stop infections. Farmers can also use certified seed without harmful parts. In special cases, scientists have made rice plants using genetically engineered methods to fight the fungus better. The disease is usually worse in moist soil that stays around 15–18 °C (59–64 °F).

Economic importance

Rhizoctonia solani is a harmful fungus that can affect many crops in the United States. It can cause problems for farmers, sometimes reducing crop yields by a lot. The fungus also makes the soil stick to the crops, which can lower the quality of products made from them. One of the biggest problems it causes is a disease called sheath blight, which is a serious problem for rice plants.

Mycorrhizal association with orchids

Rhizoctonia solani is a type of fungus that can partner with orchids. These partnerships are called mycorrhizal associations. Some strains of the fungus can harm plants, while others are harmless. This relationship helps orchids grow and stay healthy.

Genome

Scientists have studied the genes of a type of fungus called Rhizoctonia solani. They found its DNA has about 51.7 million pieces. The real amount is probably bigger because some parts were hard to read. This fungus may have around 12,726 genes that help it grow and stay alive. Researchers are studying other types of this fungus to learn more.