Rice stem rot is a disease that affects rice crops worldwide. It was first identified in Italy in 1876 and later reported in India in 1911. A type of fungus, Sclerotium oryzae, causes the disease. It is particularly harmful to rice plants during the vegetative and reproductive stages.
When a rice plant is infected with stem rot, it can result in wilting and death of the plant. The disease can lead to significant yield losses, especially in humid and warm growing conditions. The disease can be particularly severe during August and September, leading to up to 75-100% crop losses.
The disease affects all crop yield components, such as the number of productive tillers and the number of grains produced per panicle. Stem rot disease can lead to the formation of lesions, chalky grains, and unfilled panicles. Stem rot has been detected in rice-growing regions across the world, including Japan, China, the Philippines, Ceylon, Italy, Brazil, and the United States of America.
Stem Rot disease management in Paddy
The causal organism of Rice Stem Rot disease
- Nakataea sigmoidea and Sclerotium oryzae are two fungus stages that affect rice crops.
- The fungus grows as a greyish-white to pale-olive mycelium and produces small black sclerotia.
- In the conidial stage, the fungus produces dark, nodular conidiophores with pale-olivaceous conidia.
- The sexual stage of the fungus, Magnaporthe Salvini, produces globose, black perithecia containing clavate asci and oblong ascospores.
- The fungus affects the growth of the culm and leaf sheath of the rice plant and produces sclerotia.
- Sclerotia, or infection bodies, are found in the topsoil layer. They can live in air-dry soil, damp rice soil, and tap water.
The Disease cycle of Rice Stem Rot disease
- The disease caused by Sclerotium oryzae is a late-season, soil-borne disease.
- It develops rapidly during the reproductive stage of the rice plant, around its physiological maturity.
- The pathogen perennates through sclerotia in the soil and can persist for several months or even two years in stubbles.
- The sclerotia can spread from field to field or plant to plant by floating on water.
- Sclerotia are responsible for primary infection, while conidia produced can cause secondary infections through spread in irrigation water.
- They may also live on straw that has been buried in the soil. During soil preparation, sclerotia float on irrigation water and infect newly planted rice.
Favorable conditions for the spread of Rice Stem Rot disease
- High nitrogen levels promote stem rot, although potassium mitigates the adverse effects of excess nitrogen.
- Phosphorus promotes the disease as well, but to a lesser extent.
- Silica prevents the disease.
- Early-seeded crops and early-maturing varieties are more affected.
- Infection is common in plants that have wounds from lodging or insect assault. Plants infected with stem borers have a disease incidence two or three times greater.
- Disease development is also influenced by panicle moisture content.