Sheath rot of rice

Sheath rot of rice is a significant fungal disease caused by the pathogen Sarocladium oryzae. This fungus primarily attacks the leaf sheaths that enclose the young rice panicle during its development. It is a major constraint in rice-producing regions globally, leading to substantial yield losses if not managed correctly.

The host range is primarily limited to rice (Oryza sativa). The fungus thrives on plant debris and can be seed-borne, meaning that infected seeds serve as a primary source of inoculum for the next planting season. The interaction between the pathogen and the host plant is most critical during the booting and heading stages of the rice life cycle.

Diagnostic symptoms include oblong or irregular lesions on the uppermost leaf sheaths. These lesions typically have greyish centers with dark brown margins. As the infection progresses, the lesions enlarge and coalesce, eventually covering the entire sheath. A white, powdery growth of fungal mycelia and conidia often develops inside the sheath, preventing the panicle from emerging properly.

Environmental conditions such as high humidity (above 80%) and temperatures between 25°C and 30°C are ideal for the development and spread of Sarocladium oryzae. Furthermore, injuries to the leaf sheaths, frequently caused by stem borers or other insects, facilitate the penetration of the fungus into the plant tissues, significantly exacerbating the severity of the infection.

The impact of sheath rot includes empty or partially filled panicles, poor grain quality, and reduced overall weight. To mitigate these risks, the following management strategies are recommended:

• Selection of resistant or tolerant rice varieties.
• Implementation of proper crop rotation to break the disease cycle.
• Judicious use of nitrogen fertilizers to avoid overly succulent plant tissue.
• Effective pest control to prevent physical damage to leaf sheaths.
• Application of appropriate fungicides during the early stages of disease appearance.