How to Identify, Prevent, and Control 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.
FAQs on Rice Bacterial Blight: Key Facts, Symptoms, and Solutions
1. What is Rice Bacterial Blight?
Rice Bacterial Blight is a serious and widespread disease affecting rice crops, particularly in Asia. It is caused by the bacterium Xanthomonas oryzae pv. oryzae. The infection leads to significant damage to the plant's leaves, reducing its photosynthetic ability and resulting in substantial yield losses.
2. What are the main symptoms of Rice Bacterial Blight?
The primary symptoms of Rice Bacterial Blight depend on the stage of infection and the plant's age. Key signs to look for include:
- Water-soaked lesions: These appear as long, wavy, water-soaked streaks starting from the leaf tips and margins.
- Yellowish-grey streaks: As the disease progresses, the lesions turn yellowish-grey and spread down the leaf.
- Kresek or Wilt Phase: In young seedlings, a severe systemic infection can cause the entire plant to wilt and die, a condition known as 'kresek'.
3. What is the causal organism of Rice Bacterial Blight?
The causal organism responsible for Rice Bacterial Blight is a gram-negative bacterium named Xanthomonas oryzae pv. oryzae. This pathogen specifically targets rice plants and is known for its ability to spread rapidly under favourable environmental conditions.
4. How does Rice Bacterial Blight spread from one plant to another?
Rice Bacterial Blight primarily spreads through various means, making it highly contagious in a field. The main transmission pathways include:
- Infected seeds: The bacteria can be present in or on the seeds, leading to infection in the next generation of crops.
- Water sources: Pathogens can travel through irrigation water, spreading from infected to healthy plants.
- Wind and rain: Wind-driven rain can splash bacteria from infected leaves onto healthy ones, especially during monsoon seasons.
- Contaminated equipment: Farm tools and machinery can also carry the bacteria between fields if not properly cleaned.
5. What are the most effective management strategies for Rice Bacterial Blight?
Effective management of Rice Bacterial Blight involves an integrated approach combining cultural, biological, and chemical methods. The most crucial strategies are:
- Planting disease-resistant rice varieties, which is the most sustainable solution.
- Using certified, disease-free seeds to prevent initial infection.
- Ensuring proper field sanitation and managing irrigation water to reduce spread.
- Applying copper-based bactericides or antibiotics like streptocycline as a last resort and under expert guidance.
6. Is Rice Blight a fungal or bacterial disease?
This is a common point of confusion. Rice Bacterial Blight is, as its name suggests, a disease caused by the bacterium Xanthomonas oryzae. However, rice is also affected by other diseases with similar names, such as Sheath Blight, which is caused by the fungus Rhizoctonia solani. It is essential to distinguish between them as their treatments are different.
7. How does Bacterial Blight differ from Sheath Blight in rice?
While both are major rice diseases, they are caused by different pathogens and show distinct symptoms. Bacterial Blight is caused by a bacterium and appears as long, yellowish, wavy lesions starting from leaf tips. In contrast, Sheath Blight is caused by a fungus and typically starts as oval, greyish-green lesions on the leaf sheath, usually just above the waterline.
8. What environmental conditions favour the outbreak of Rice Bacterial Blight?
Outbreaks of Rice Bacterial Blight are heavily influenced by environmental factors. The disease thrives in conditions of high humidity (above 70%) and warm temperatures, typically between 25°C and 30°C. The presence of strong winds and heavy rainfall during the growing season significantly accelerates the spread of the bacteria from plant to plant.
9. Why is developing disease-resistant rice varieties considered the best long-term solution?
Developing disease-resistant rice varieties is the most economical and environmentally sustainable strategy for managing Bacterial Blight. Unlike chemical controls, which require repeated application and can have ecological side effects, resistant varieties provide inherent protection. This reduces costs for farmers, minimises environmental pollution, and ensures more stable crop yields.
10. What is the economic importance and impact of Rice Bacterial Blight?
The economic impact of Rice Bacterial Blight is immense, especially in major rice-producing countries. The disease can cause severe yield losses, which can range from 20% to over 50% in susceptible varieties under favourable conditions. This not only leads to significant financial losses for individual farmers but can also impact national food security and the stability of rice markets.
