Stem rot of rice

Stem rot is a severe fungal disease caused by the pathogen Sclerotium oryzae (teleomorph Magnaporthe salvinii). This fungus targets the stem tissues of susceptible plants, leading to severe structural failure, lodging, and significant yield losses in commercial production cycles.

The host range of Sclerotium oryzae is broad, affecting various crops beyond rice, including peanuts, papaya, poinsettia, common beans, potatoes, and wild species like Zizania. The pathogen survives in the soil and on crop debris as small, dark, round sclerotia, which can remain viable for several years.

Disease symptoms typically start as dark lesions on the leaf sheaths near the waterline. As the fungus progresses, it penetrates the inner stem tissue, where it produces numerous black sclerotia. This weakens the plant's structural integrity, causing it to lodge, while grain filling is interrupted, often resulting in empty or shriveled panicles.

Conditions favoring the spread of stem rot include prolonged high humidity and temperatures between 25°C and 30°C. The disease spreads rapidly through infested irrigation water and movement of soil containing sclerotia. Agronomic practices that promote excessive canopy density or high nitrogen availability often exacerbate the severity of the infection.

Effective management requires an integrated approach. Cultural practices such as removing crop residues, implementing proper crop rotation, and optimizing plant spacing are crucial. Farmers should monitor nitrogen levels to prevent overly succulent growth and apply registered fungicides when the initial symptoms appear to minimize the spread and impact of the fungus.