Xanthomonas oryzae pv. oryzae
On seedlings, infected leaves first turn yellow to straw-colored and later wilt and die. On mature plants, the period of occurrence is mainly from tillering to panicle formation. Light green to grayish green, water-soaked streaks appear first on leaves. As they merge, they form larger yellowish lesions with uneven edges. Leaves become chlorotic and gradually wilt and die. In the final stage of infection, milky bacterial ooze can be observed dropping from the leaves. These drops can later dry up and leave a white encrustation. This trait can help to distinguish this disease from the damage caused by some stem borers. Bacterial blight is one of the most serious diseases of rice.
Symptoms are caused by the bacteria Xanthomonas oryzae pv. oryzae, which can survive on grass weeds or stubbles of infected plants. These pathogens are spread by wind and rain splash or irrigation water. Thus, disease incidence and severity are increased during bad weather (frequent rainfall, wind), high humidity (above 70%) and warm temperatures (25°C to 34°C). High nitrogen fertilization or close planting also favors the disease, particularly in susceptible varieties. The earlier the disease occurs, the higher the yield loss. When plants are infected during the development of the panicle, yields can be unaffected but a high proportion of the grains is broken. The disease occur in both tropical and temperate environments, particularly in irrigated and rain-fed lowland areas.
To this day, no biological products are commercially available to the control bacterial blight in rice. The application of products based on copper can help to alleviate or reduce the symptoms but will not control the disease.
Always consider an integrated approach with preventive measures and biological treatments if available. To combat bacterial blight, the treatment of seeds with an authorized antibiotic plus copper oxychloride or copper sulfate has been recommended. The use of antibiotic is severely restricted in some countries, so please check measures in force in your country.
Use only healthy or certified seeds.,Plant resistant rice varieties is the most efficient, reliable way to control the pathogen (and the cheapest!).,Handle the seedling carefully during transplanting.,Ensure proper drainage of the fields and nursery to avoid cross-contamination.,Destroy and remove weeds and alternative hosts from channels and surroundings.,Plow under rice stubble, straw, ratoons and volunteer seedlings which can serve as hosts for the bacteria.,Adjust nitrogen fertilizer applications to avoid excess and split the applications over the season.,Apply an extra dose of potash along with last dose of nitrogen when weather conditions are favorable.,Allow the fields to dry between the seasons in order to suppress disease agents in the soil and plant residues (fallow).,Avoid application of nitrogen in the form of urea.