Model Answer
0 min readIntroduction
Crop diseases pose a significant threat to global food security, causing substantial yield losses and economic damage. Fungal pathogens are responsible for a large proportion of these diseases, owing to their prolific spore production, diverse infection strategies, and adaptability. Understanding the causal organisms, recognizing symptoms, and implementing effective control measures are crucial for sustainable agricultural practices. India, with its diverse agro-climatic zones, is particularly vulnerable to a wide range of fungal crop diseases. This answer will detail four important fungal diseases affecting major Indian crops.
Four Important Fungal Crop Diseases
1. Rust of Wheat (Puccinia graminis f. sp. tritici)
Causal Organism: Puccinia graminis f. sp. tritici, a basidiomycete fungus.
Symptoms: Rust appears as reddish-brown, elongated pustules on leaves, stems, and sometimes even on grains. These pustules contain masses of urediniospores. Severe infection leads to reduced grain filling, shriveled grains, and significant yield loss. Different forms of rust (black rust, brown rust, yellow rust) exist, each with slightly different symptoms but all causing substantial damage.
Control Measures:
- Resistant Varieties: Cultivating wheat varieties with resistance genes (e.g., Sr genes) is the most effective control measure.
- Seed Treatment: Treating seeds with fungicides like carboxin or tridemorph.
- Foliar Spray: Applying systemic fungicides like propiconazole or tebuconazole at early stages of infection.
- Crop Rotation: Rotating wheat with non-host crops to break the disease cycle.
- Sanitation: Removing and destroying infected plant debris.
2. Late Blight of Potato (Phytophthora infestans)
Causal Organism: Phytophthora infestans, an oomycete (often mistakenly classified as a fungus).
Symptoms: Characterized by dark, water-soaked lesions on leaves and stems, often with a white, fuzzy growth on the underside of leaves. Tubers develop reddish-brown lesions that can rot rapidly. The disease spreads rapidly in cool, moist weather.
Control Measures:
- Disease-Free Seed: Using certified disease-free seed potatoes.
- Prophylactic Spraying: Applying copper-based fungicides (e.g., copper oxychloride) or systemic fungicides like mancozeb preventatively.
- Earthing Up: Hilling up the potato plants to protect tubers from infection.
- Crop Rotation: Avoiding continuous potato cultivation.
- Destroying Infected Plants: Removing and burning infected plants to prevent further spread.
3. Powdery Mildew of Grapevine (Erysiphe necator)
Causal Organism: Erysiphe necator, an ascomycete fungus.
Symptoms: Appears as a white, powdery coating on leaves, shoots, and berries. Severe infection can lead to leaf distortion, reduced photosynthesis, and cracking of berries, making them susceptible to secondary infections.
Control Measures:
- Pruning: Proper pruning to improve air circulation and sunlight penetration.
- Fungicide Application: Using systemic fungicides like myclobutanil or difenoconazole, or protectant fungicides like sulfur.
- Resistant Varieties: Selecting grapevine varieties with some level of resistance.
- Removing Infected Parts: Pruning and destroying infected shoots and leaves.
4. Blast of Rice (Magnaporthe oryzae)
Causal Organism: Magnaporthe oryzae, an ascomycete fungus.
Symptoms: Initially appears as small, circular or elliptical lesions on leaves, often with a grayish center. Lesions can rapidly expand and coalesce, causing leaf blight. On the panicle, it causes neck breakage, leading to empty grains. The disease is highly destructive and can cause significant yield losses.
Control Measures:
- Resistant Varieties: Cultivating rice varieties with resistance genes (e.g., Pi genes).
- Seed Treatment: Treating seeds with fungicides like carbendazim or tricyclazole.
- Foliar Spray: Applying fungicides like propiconazole or azoxystrobin at early stages of infection.
- Water Management: Avoiding excessive nitrogen fertilization and maintaining proper drainage.
- Crop Rotation: Rotating rice with non-host crops.
| Disease | Causal Organism | Major Symptoms | Control Measures |
|---|---|---|---|
| Rust of Wheat | Puccinia graminis f. sp. tritici | Reddish-brown pustules on leaves/stems | Resistant varieties, seed treatment, foliar spray |
| Late Blight of Potato | Phytophthora infestans | Dark lesions on leaves/tubers, white fuzzy growth | Disease-free seed, prophylactic spraying, earthing up |
| Powdery Mildew of Grapevine | Erysiphe necator | White powdery coating on leaves/berries | Pruning, fungicide application, resistant varieties |
| Blast of Rice | Magnaporthe oryzae | Circular lesions on leaves, neck breakage | Resistant varieties, seed treatment, foliar spray |
Conclusion
Fungal crop diseases represent a persistent challenge to agricultural productivity. Effective management requires an integrated approach encompassing the use of resistant varieties, appropriate cultural practices, and judicious application of fungicides. Continuous monitoring, early detection, and prompt intervention are crucial for minimizing yield losses and ensuring food security. Further research into novel disease resistance genes and environmentally friendly control strategies is essential to address the evolving threat posed by these pathogens.
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.