Rice stem rot

Nakataea oryzae is a fungal phytopathogen within the kingdom Fungi and the genus Nakataea. It is recognized globally as the primary agent responsible for stem rot disease in rice. This pathogen specifically targets the basal parts of rice plants, significantly disrupting the vascular system and physiological health of the crop.

The disease is characterized by the appearance of dark, irregular lesions on the leaf sheaths, which gradually penetrate the stem tissue. As the infection progresses, these areas soften and turn gray, often showing visible mycelium and sclerotia. This structural damage leads to premature lodging of plants and results in poorly filled grains or total crop failure if the infection occurs early in the season.

The biology of the pathogen centers on its sclerotia, which serve as the primary inoculum. These resting structures are highly resistant to adverse environmental conditions and can survive in the soil or crop debris for multiple seasons. When rice fields are flooded, these sclerotia float to the water surface, contact the rice tillers, and initiate infection through the epidermis.

Environmental conditions play a crucial role in the development of Nakataea oryzae. High relative humidity and temperatures ranging from 25°C to 30°C are optimal for the growth of the fungus. Excessive nitrogen fertilization and high plant density are major cultural factors that exacerbate the severity of the disease by creating a microclimate favorable for fungal spread.

Effective management and control strategies include:

• Selecting resistant or tolerant rice cultivars for high-risk areas.
• Implementing proper water management, including periodic drainage of rice paddies.
• Maintaining field hygiene by removing or burning crop residues after harvest.
• Applying recommended systemic fungicides at the early tillering stage to prevent establishment.