Nakataea stem rot of rice

Nakataea stem rot is a destructive fungal disease affecting rice crops worldwide, caused by the pathogen Nakataea sigmoidea. This fungus is known for its ability to survive in soil and crop debris through sclerotia, making it a persistent challenge for farmers in irrigated rice production systems.

The disease primarily impacts rice plants (Oryza sativa), although the pathogen can potentially survive on various host grasses. Rice plants are susceptible throughout their growth cycle, but the most severe damage usually occurs from the late tillering stage through the grain-filling period, when the plant is most vulnerable to systemic colonization.

Symptoms initially appear as small, dark, irregular spots on the leaf sheaths near the water level. As the infection progresses, these lesions enlarge and penetrate the stem, causing internal decay. The presence of numerous small, black, spherical sclerotia inside the diseased stem is a diagnostic indicator that confirms the infection by Nakataea sigmoidea.

The spread of the pathogen is highly dependent on environmental conditions, particularly high humidity, warm temperatures, and prolonged water saturation. Dense planting patterns and excessive nitrogen fertilization exacerbate the disease development by creating a conducive microclimate and weakening the physical structure of the rice stems, allowing the fungus to spread rapidly.

The economic impact of stem rot is significant, leading to lodging, unfilled grains, and decreased grain quality, which directly reduces total yield. To effectively manage and mitigate the risk, the following practices are recommended:

• Selection and planting of disease-resistant rice varieties.
• Deep plowing and removal of infected crop residues to reduce primary inoculum.
• Balanced fertilization, avoiding excessive nitrogen that promotes lush, susceptible tissue growth.
• Proper water management, including periodic drainage of rice paddies to expose the soil.
• Application of targeted fungicides as part of an integrated pest management program.