Sheath brown rot

Pathogen and disease type. Sheath brown rot is a bacterial disease caused by the pathogen Pseudomonas fuscovaginae. This bacterium is known for its ability to colonize the leaf sheaths of host plants, causing severe necrotization. It is considered a significant threat in rice-producing regions globally, leading to substantial losses in agricultural productivity.

Host crops. The primary host for Pseudomonas fuscovaginae is rice (Oryza sativa). The pathogen is highly adapted to the specific microclimate of flooded rice paddies. It is often seed-borne, meaning the infected seeds serve as the primary inoculum for the next growing season, facilitating the spread of the disease over long distances.

Symptoms and signs. Typical symptoms include the appearance of dark, water-soaked, and necrotic lesions on the leaf sheaths. As the disease advances, these lesions turn brown or reddish-brown. A key diagnostic feature is the failure of the panicle to emerge properly from the sheath (sheath rot), which often results in empty or discolored grains, significantly reducing the yield quality.

Conditions for development and spread. The bacteria thrive in cool to moderate temperatures and high humidity, which are often characteristic of the tillering and heading stages of rice. Spread is facilitated by irrigation water, rainfall, and infected plant debris. High nitrogen fertilization and dense planting exacerbate the severity of the outbreak by providing a favorable environment for bacterial multiplication.

Harmfulness and control measures. The disease can cause significant economic damage by affecting grain filling and panicle development. Effective control requires an integrated approach. Recommendations include sourcing pathogen-free seeds, implementing hot water treatment for seeds, improving field drainage to manage humidity, and practicing strict sanitation to remove infected crop residue from the fields.