Bacterial brown stripe

The causal agent of bacterial brown stripe in rice is the gram-negative bacterium Acidovorax oryzae. This pathogen is recognized as a significant threat to rice production globally, particularly in tropical and subtropical regions. It invades the vascular tissues of the plant, disrupting the transport of nutrients and water, which ultimately leads to severe physiological stress and reduced grain yield.

The primary host for this pathogen is rice (Oryza sativa), although it has been documented affecting other graminaceous weeds. The disease cycle begins either from infected seeds or from contaminated soil and irrigation water. The bacteria survive in seeds and plant debris, making long-distance transmission through seed trade a major concern for biosecurity in rice-growing regions.

Symptoms initially appear as water-soaked, narrow, translucent streaks on the leaves. As the disease progresses, these lesions turn brown or reddish-brown. In severe cases, the infected leaves wilt and curl. A distinctive feature is the presence of bacterial exudate on the lesions under high-humidity conditions, which acts as a primary source of inoculum for secondary spread throughout the field.

The development of the disease is highly dependent on environmental factors, with temperatures between 28°C and 32°C and high relative humidity being optimal for infection. Rain splashing and wind are the primary mechanisms for the spread of bacteria between plants. Poor drainage in rice paddies further exacerbates the issue by creating a conducive environment for bacterial multiplication.

Management requires an integrated approach that prioritizes prevention. Key practices include using high-quality, certified, and disease-free seeds and performing seed disinfection. Cultural practices such as maintaining proper spacing between plants to improve airflow and avoiding excessive nitrogen fertilizer application are crucial. In severe cases, copper-based bactericides can be used, though resistant varieties remain the most effective long-term solution.