Rice Bacterial Blight

Rice bacterial blight is one of the deadly bacterial diseases, which is the most destructive affliction of cultivated rice (Oryza sativa and O. glaberrima). It is also known as the bacterial blight of rice. Bacterial leaf blight of rice is caused by a species of Xanthomonas. Almost, 75 percent of the crops would be destroyed in severe epidemics and millions of hectares of rice are infected annually. This disease was first found in Kyushu, Japan (1884 - 1885), and the causal agent like bacterium Xanthomonas oryzae was first identified in 1911 at that time, this was named Bacillus oryzae.

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Diagram represents the symptoms of the disease on leaves with water-soaked streaks that widen, lengthen, and turn yellow.

Bacterial leaf blight of rice is most commonly observed in rice-growing regions of Asia, the western coast of Africa, Australia, Latin America, and the Caribbean regions. In places like the United States, bacterial blight is not found but a bacterial strain related to Xoo has been listed as a select agent by the US Department of Agriculture. It is a designation that places it under strict regulations. The common name of the rice bacterial leaf blight is also known as rice leaf blight. 

Bacterial Blight of Rice Symptoms

When a seedling of the rice plant is affected by the disease, the infected leaves first turn yellow to straw coloured, and later it would wilt and die. And in mature rice plants, it mainly occurs from tillering to panicle formation. Primarily the plant is light green to greyish green and water-soaked streaks appear on the leaves but once it gets affected by the bacterial blight, they form larger yellowish lesions with uneven edges. Further, the leaves become yellow, gradually wilt and die.  In the final stage of the bacterial blight, a milky bacterial ooze is observed dripping from the leaves, this can be left to dry finally a white crust can be observed. 

Effect of Bacterial Blight

Symptoms of bacterial blight of rice are caused by  Xanthomonas oryzae, which can survive on grass weeds or the stubbles of infected plants. These pathogens are spread through the wind, a splash of rain, or irrigational water. This disease spreads more during bad weather conditions like frequent rainfall, wind, and high humidity more than 70 percent, and warm temperature ranging from 25 to 34-degree celsius. More nitrogen fertilizers in the field favours the disease, particularly in susceptible varieties. Rice blight disease is found in both tropical and temperate environments, particularly in lowland rainfed areas. 

Method of Controlling Rice Blight 

There are methods to control rice blight: biological control and chemical control.

Biological Control - Till today there is no biological product, available commercially to control bacterial rice blight. But there are some of the products based on copper that would help to reduce the symptoms but cannot control the disease.

Chemical Method -  To fight against bacterial blight, rice seeds are treated with authorized antibiotics with copper oxychloride or copper sulfate has been recommended.  In some of the countries the use of antibiotics is prohibited, So go through your country guidelines before using them. 

Preventive Measures of Bacterial Blight

Some of the preventive measures taken to prevent bacterial blight of paddy (rice) are:

• It can be prevented by using healthy seeds, like from a certified source.

• Bacterial blight-resistant rice varieties, it is one of the most effective and reliable ways to control diseases, and also it is one of the cheapest ways of prevention.

• By properly handling the seedlings during transplanting.

• By properly adjusting the nitrogen fertilizers and by applying the extra dose of potash along with the last dose of nitrogen, when weather conditions are favourable.

• By avoiding the use of nitrogen in the form of urea.

• By removing a weed and other hosts from the rice field and by ploughing under rice stubble, straw, ratoons,  and volunteer seedlings can serve as hosts for the bacteria. 

• Leave the land uncultivated in between the season to suppress the disease agents in the soil and plant residues.  

Do You Know?

Which gene of rice is resistant to bacterial blight? The Xa1 gene in rice is resistant to Japanese race 1 Xanthomonas oryzae. Oryzae is the causative agent of bacterial blight. This gene of rice is highly resistant to race 1 strains of Xoo in japan.