Model Answer
0 min readIntroduction
Tungro disease is a devastating viral disease affecting rice crops, particularly prevalent in Southeast Asia and increasingly observed in other regions. The name "Tungro" originates from the Ho language of Vietnam, meaning “shoestring,” a reference to the characteristic symptom observed in affected plants. The disease significantly reduces rice yields and poses a considerable threat to food security in vulnerable regions. The recent surge in its prevalence, linked to climate change and altered cropping patterns, warrants a comprehensive understanding of its etiology, symptoms, and effective management strategies. This answer will detail the causal organism, observable symptoms, and various management practices for Tungro disease in rice.
Causal Organism and Transmission
Tungro disease is primarily caused by two distinct viruses: Rice tungro virus (RTV) and Rice tungro spherical virus (RTSV). These are not single pathogens but are transmitted through the white-backed planthopper (WBPH), *Nilaparvata lugens*, and brown planthopper (BPH), *Blocmus amylophagus*. These insects act as vectors, acquiring the viruses during feeding and transmitting them to healthy rice plants through stylet punctures. RTV is filamentous, while RTSV is spherical, and co-infection results in more severe symptoms. The virus is non-persistent, meaning it doesn't remain viable within the insect for long, limiting the transmission distance.
Symptoms of Tungro Disease
The symptoms of Tungro disease manifest in distinct stages, making diagnosis crucial. Early symptoms are often subtle and can be easily overlooked. The disease presents in two main forms: acute and chronic.
- Acute Tungro: This form is most severe and results from infection during the seedling stage. Affected plants exhibit stunted growth, yellowing (chlorosis) of the leaves, and "shoestring" appearance – the leaves become narrow, elongated, and brittle. Panicle blast (premature panicle sterility) is common, leading to complete yield loss.
- Chronic Tungro: Infection during the tillering stage results in a less severe, chronic form. While growth is still stunted, the plant may survive and produce a reduced yield. The “shoestring” symptom is less pronounced, and panicle blast is less common.
The characteristic “shoestring” symptom is a result of the virus disrupting chlorophyll synthesis and affecting cell elongation.
Management of Tungro Disease
Managing Tungro disease requires an integrated approach, focusing on prevention and suppression of the vector insects. There is no specific cure for the virus itself.
Preventive Measures
- Vector Control: This is the most critical aspect of Tungro management.
- Monitoring and Trapping: Regular monitoring of planthopper populations using sticky traps (yellow and blue) helps assess infestation levels and guide control measures.
- Insecticides: Judicious use of insecticides targeting nymph and adult stages of WBPH and BPH can reduce vector populations. However, overuse can lead to resistance.
- Biological Control: Promoting natural enemies of planthoppers, such as spiders, predatory insects, and parasitoids, can help suppress their populations. *Orius* species are known predators.
- Resistant Varieties: Developing and deploying rice varieties resistant to Tungro virus and/or the planthopper vectors is a sustainable solution. Several resistant varieties have been released in affected regions.
- Crop Rotation & Intercropping: Rotating rice with non-rice crops or intercropping with legumes can disrupt the life cycle of the vectors and reduce disease incidence.
- Weed Management: Controlling weeds that serve as alternate hosts for the planthoppers is important.
- Sowing Time: Adjusting sowing time to avoid peak planthopper activity periods can reduce initial infestation pressure.
Curative Measures
- Roguing: Removing and destroying infected plants early on can prevent further spread.
- Nutrient Management: Balanced fertilization, particularly with nitrogen and potassium, can improve plant vigor and resilience to the disease.
- Plant Growth Regulators (PGRs): Some PGRs have shown limited efficacy in alleviating symptoms and improving yield, but their use is not widely recommended.
Integrated Pest Management (IPM)
The most effective approach involves an IPM strategy, combining multiple control measures. The FAO recommends a systems approach including resistant varieties, biological control, and careful insecticide use. The National Plant Protection Authority (NPPA) in affected countries plays a crucial role in coordinating and implementing Tungro disease management programs.
| Management Strategy | Description | Effectiveness |
|---|---|---|
| Resistant Varieties | Using rice varieties with genetic resistance to Tungro virus. | High, sustainable |
| Biological Control | Utilizing natural predators of planthoppers. | Moderate, requires ecosystem support |
| Insecticide Application | Targeting planthopper nymphs and adults. | Short-term, risk of resistance |
| Crop Rotation | Rotating rice with non-rice crops. | Moderate, long-term benefit |
Conclusion
Tungro disease remains a significant challenge for rice production globally. Understanding the viral etiology, recognizing the characteristic symptoms, and implementing a comprehensive integrated pest management strategy are crucial for effective control. The development and dissemination of resistant rice varieties, coupled with sustainable vector control practices, represent the most promising long-term solutions. Continuous monitoring, research, and farmer education are essential to mitigate the impact of this devastating disease and ensure food security in vulnerable regions. Future research should focus on identifying novel biological control agents and developing more durable resistance genes.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.