Rice sheath rot

Sarocladium oryzae is a plant pathogenic fungus classified within the Sarocladium genus. It is the primary causal agent of rice sheath rot, a destructive disease that affects rice crops worldwide. This fungus focuses its attacks on the leaf sheaths enclosing the young panicle, severely impacting the reproductive development of the plant.

The characteristic symptoms of the disease include oblong or irregular lesions on the leaf sheaths. These lesions initially appear as greyish-white or light brown spots, which eventually expand and turn dark brown with a distinct border. Under high humidity, an abundant white powdery growth of fungal spores is observed inside the leaf sheath, which physically hinders the panicle from emerging properly.

The biology and lifecycle of Sarocladium oryzae are highly dependent on environmental conditions. The pathogen survives in soil, infected seeds, and crop debris from the previous season. Its development is favored by temperatures ranging from 25°C to 30°C and high relative humidity. The fungus spreads through irrigation water, rainfall splashing, and insect vectors that create entry wounds on the rice stems, facilitating infection.

The agricultural impact of this disease is significant, as it leads to both reduced grain yield and poor quality. Infected plants often produce unfilled grains (sterile panicles), which directly lowers the total harvest. Furthermore, the presence of the fungus can lead to grain discoloration and reduced germination potential, making the harvest less valuable for commercial distribution and milling.

Integrated disease management strategies are essential for effective control:

• Selecting and planting resistant or tolerant rice varieties.
• Practicing crop rotation and thorough sanitation of rice fields post-harvest.
• Managing nitrogen fertilization levels, as excessive nitrogen increases plant susceptibility.
• Seed treatment with appropriate systemic fungicides before planting.
• Applying foliar fungicides during the booting stage to prevent initial infection spread.