Rice sheath rot

Acrocylindrium oryzae, widely known in modern taxonomy as Sarocladium oryzae, is a fungus responsible for the devastating rice disease known as sheath rot. It belongs to the Ascomycota phylum and is categorized as a significant phytopathogen that causes serious economic losses in rice-growing regions globally, particularly in tropical and subtropical climates.

The disease primarily manifests on the flag leaf sheaths that enclose the young panicle. Infected areas show irregular, elongated, or oval spots with dark brown margins and gray or white necrotic centers. When the infection is severe, the fungal mycelium colonizes the interior of the sheath, preventing the panicle from emerging properly, leading to grain sterility and reduced milling quality.

The biology of Acrocylindrium oryzae involves the production of conidia that are easily dispersed by wind, rain splashes, and insects. The pathogen survives between cropping seasons in infected rice straw, soil, and dormant seeds. It requires a humid environment to trigger spore germination and tissue penetration, often utilizing wounds created by stem borers to enter the host plant.

Environmental conditions play a crucial role in disease development. High relative humidity and warm temperatures during the panicle initiation stage are ideal for the pathogen. Agronomic practices that promote excessive canopy density, such as high planting density and high nitrogen fertilizer application, significantly increase the risk of rapid disease transmission within the field.

Management of rice sheath rot requires an integrated pest management (IPM) strategy. Key control measures include the cultivation of resistant or tolerant rice varieties, crop rotation to break the infection cycle, and the removal of infected plant residues. Chemical intervention, through the application of systemic fungicides at the early booting stage, remains the most effective way to protect yield potential.

• Balanced application of potassium and nitrogen fertilizers.
• Use of certified pathogen-free seeds.
• Monitoring for secondary infestations by insects.
• Timely fungicide sprays at the booting stage.