Sheath rot of rice

The fungus Sarocladium attenuatum (often linked to the Acremonium genus) is the causal agent of sheath rot in rice. This pathogen colonizes the leaf sheaths and spreads rapidly, utilizing the plant's resources to produce its characteristic mycelial growth, which manifests as pale or greyish masses on the infected tissues.

Rice (Oryza sativa) is the primary host of this pathogen. The infection specifically targets the leaf sheaths that enclose the emerging panicle. When the infection is severe, it prevents the panicle from fully emerging, leading to significant physiological stress and failure in the reproductive cycle of the crop.

Symptoms typically appear as oblong, irregular lesions with dark brown margins and grey or white centers on the upper leaf sheaths.

• Necrosis of the sheath tissues
• Incomplete panicle emergence
• Discoloration and decay of the grain
• Reduced grain filling and viability

Development and spread are strongly favored by high humidity (80–90%), frequent rainfall, and temperatures ranging from 20°C to 30°C. These conditions are common in many rice-growing regions during the heading stage. Furthermore, high nitrogen fertilization rates can exacerbate the disease by creating denser, more susceptible plant tissues.

Management of sheath rot requires an integrated pest management (IPM) approach. This includes the use of resistant rice cultivars, appropriate plant spacing to improve aeration, and balanced fertilization. Chemical control involves the application of systemic fungicides specifically targeted at the booting stage to suppress fungal growth and protect the developing panicles from initial infection.