Model Answer
0 min readIntroduction
Bajra ( *Pennisetum glaucum* L.) is a staple food crop in arid and semi-arid regions of India, known for its resilience and nutritional value. However, its production is often threatened by various diseases, among which 'Green ear disease' is a significant constraint. This disease, first reported in Rajasthan in 1978, causes substantial yield losses, particularly during years with high humidity and rainfall. Understanding the disease's biology and developing effective management strategies are crucial for ensuring food security in Bajra-growing regions.
Etiology and Symptoms
The Green ear disease of Bajra is caused by the fungus *Sclerospora graminicola*, an obligate parasite belonging to the Oomycetes group. The disease primarily affects the ear head, hence the name. Key symptoms include:
- Early Stage: Appearance of pale green or yellowish streaks on the ear head.
- Progressive Stage: The infected ear head becomes swollen, elongated, and covered with a greenish-white, slimy exudate containing numerous sporangia.
- Late Stage: The ear head becomes brittle, breaks easily, and the grains are often sterile or poorly developed.
- Systemic Infection: In severe cases, the disease can spread to the stem and leaves, causing similar symptoms.
Disease Cycle
The disease cycle of *Sclerospora graminicola* is complex and involves several stages:
- Survival: The fungus survives in soil and infected plant debris as oospores.
- Sporulation: Oospores germinate under favourable conditions (high moisture and temperature) to produce sporangia.
- Infection: Sporangia release zoospores, which are motile in water and infect the Bajra plant through stomata or wounds.
- Systemic Spread: Once inside the plant, the fungus spreads systemically, reaching the ear head.
- Secondary Infection: Sporangia are produced on the infected ear head, leading to secondary infection.
Epidemiological Factors
Several factors favour the development and spread of Green ear disease:
- High Humidity: Relative humidity above 80% is conducive for sporangia formation and zoospore release.
- Rainfall: Frequent rainfall or irrigation creates a favourable environment for zoospore movement and infection.
- Temperature: Optimal temperature for disease development is between 25-30°C.
- Dense Planting: High plant density reduces air circulation and increases humidity within the crop canopy.
- Susceptible Varieties: Certain Bajra varieties are more susceptible to the disease than others.
- Nitrogen Imbalance: Excessive nitrogen fertilization can increase the susceptibility of plants.
Management Strategies
Effective management of Green ear disease requires an integrated approach:
Cultural Practices
- Seed Treatment: Treating seeds with fungicides like carboxin or metalaxyl.
- Resistant Varieties: Cultivating resistant or tolerant Bajra varieties (e.g., PBR 333, HB 313).
- Optimum Sowing Time: Adjusting sowing time to avoid peak disease incidence periods.
- Proper Plant Density: Maintaining optimal plant density to ensure good air circulation.
- Balanced Fertilization: Applying balanced doses of fertilizers, avoiding excessive nitrogen.
- Crop Rotation: Rotating Bajra with non-host crops.
- Removal of Infected Debris: Removing and destroying infected plant debris to reduce inoculum.
Chemical Control
In severe cases, chemical control may be necessary:
- Fungicides: Spraying systemic fungicides like propiconazole or tricyclazole at the early stages of disease development.
- Preventive Spraying: Prophylactic spraying of fungicides during favourable weather conditions.
Impact on Bajra Production
Green ear disease can cause significant yield losses in Bajra, ranging from 20% to 80% depending on the severity of the infection and the susceptibility of the variety. This impacts the livelihoods of farmers in arid and semi-arid regions and contributes to food insecurity. The disease also reduces the quality of the grain, making it less suitable for consumption and processing.
Conclusion
Green ear disease remains a major threat to Bajra production in India. A holistic approach integrating resistant varieties, cultural practices, and judicious use of fungicides is essential for effective disease management. Further research is needed to develop more durable resistance and environmentally friendly control strategies. Strengthening disease surveillance and providing timely advisory services to farmers are also crucial for minimizing yield losses and ensuring food security.
Answer Length
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