Wilt Disease of Gram (Chickpea)
Causal Organism
Name: Fusarium oxysporum f. sp. ciceri
Classification:
Kingdom: Fungi
Phylum: Ascomycota
Class: Sordariomycetes
Order: Hypocreales
Family: Nectriaceae
Genus: Fusarium
Species: Fusarium oxysporum
Formae Speciales: ciceri (specific to chickpeas)
Symptoms
Wilting:
The most characteristic symptom is the sudden wilting of plants without any obvious external signs of decay.
Yellowing:
Older leaves turn yellow, followed by the entire plant wilting and drying out.
Vascular Discoloration:
Brown or black streaks can be observed in the vascular tissues of roots and stems when cut open.
Stunting:
Affected plants may be stunted with fewer and smaller leaves.
Leaf Drop:
Premature leaf drop occurs, leading to defoliation.
Death:
In severe infections, plants may die before reaching maturity.
Etiology
Pathogen Introduction: Fusarium oxysporum f. sp. ciceri is a soilborne fungus that infects chickpea plants through the roots.
Favorable Conditions: Warm soil temperatures (2530°C or 7786°F) and moderate moisture levels favor the pathogen's growth and infection.
Infection Process: The fungus invades the plant through root hairs or wounds, colonizing the vascular system and disrupting water and nutrient transport.
Persistence: The pathogen can survive in the soil for many years as chlamydospores (thickwalled resting spores) or as mycelium in plant debris.
Disease Cycle
1. Overwintering:
The fungus survives in the soil or plant debris as chlamydospores or mycelium.
2. Germination:
Under favorable conditions, chlamydospores germinate and produce hyphae that infect chickpea roots.
3. Colonization:
The fungus colonizes the vascular system, producing microconidia that spread the infection within the plant.
4. Symptom Expression:
Infected plants exhibit symptoms such as wilting, yellowing, stunting, and vascular discoloration.
5. Sporulation:
The fungus produces more chlamydospores in the decaying plant tissues, which are released into the soil upon decomposition.
6. Reinfection:
The cycle repeats when new chickpea plants are grown in the contaminated soil.
Management
1. Cultural Practices:
Crop Rotation: Practice crop rotation with nonhost crops (e.g., cereals) for 34 years to reduce soil inoculum levels.
Resistant Varieties: Use chickpea varieties that are resistant or tolerant to Fusarium wilt. Breeding programs have developed several resistant cultivars.
Soil Health: Improve soil health through organic amendments and proper drainage to suppress the pathogen's activity.
Sanitation: Remove and destroy infected plant debris after harvest to reduce the source of inoculum.
2. Chemical Control:
Soil Treatment: Soil fumigation or solarization before planting can reduce the pathogen load in the soil, but these methods can be costly and have environmental impacts.
Seed Treatment: Treating seeds with fungicides (e.g., carbendazim, thiram) or biocontrol agents before planting can reduce initial infection rates.
3. Biological Control:
Biocontrol Agents: Use biocontrol agents such as Trichoderma spp., Pseudomonas fluorescens, and Bacillus subtilis to suppress Fusarium oxysporum f. sp. ciceri in the soil.
Mycorrhizae: Arbuscular mycorrhizal fungi can improve plant health and resistance to wilt by enhancing nutrient uptake and inducing systemic resistance.
4. Integrated Disease Management (IDM):
Combining Strategies: Implement an integrated approach that combines resistant varieties, cultural practices, chemical treatments, and biological control for effective disease management.
Monitoring and Early Detection: Regularly monitor fields for early signs of wilt and take prompt action to manage the disease.
By adopting an integrated approach and using resistant varieties, the impact of Fusarium wilt on chickpea crops can be significantly reduced, ensuring better plant health and yield.
Ascochyta Blight of Chickpea (Gram)
Causal Organism
Name: Ascochyta rabiei (syn. Phoma rabiei)
Classification:
Kingdom: Fungi
Phylum: Ascomycota
Class: Dothideomycetes
Order: Pleosporales
Family: Didymellaceae
Genus: Ascochyta
Species: A. rabiei
Symptoms
Leaf Spots:
Small, circular to irregular brown spots with concentric rings, often surrounded by a yellow halo.
Stem Lesions:
Dark brown to black lesions on stems and branches, which can girdle the stem and cause wilting and plant death.
Pod Lesions:
Brown to black spots on pods, which may enlarge and merge, leading to pod rot and seed infection.
Seed Discoloration:
Infected seeds can appear shriveled, discolored, and covered with black fungal growth.
Etiology
Pathogen Introduction: The fungus Ascochyta rabiei is introduced into crops through infected seeds, crop debris, and volunteer plants.
Favorable Conditions: Cool, wet weather conditions favor the development and spread of Ascochyta blight. Optimal temperatures for disease development range from 1525°C (5977°F) with high humidity or prolonged leaf wetness.
Spore Dispersal: The pathogen produces both pycnidiospores and ascospores. Pycnidiospores are spread by rain splash, while ascospores are winddispersed over longer distances.
Disease Cycle
1. Overwintering:
The fungus overwinters in infected crop residues, soil, and seeds.
2. Primary Infection:
In the spring, pycnidiospores and ascospores are released from overwintering structures and infect young chickpea plants.
3. Secondary Infection:
Pycnidia formed on infected tissues produce pycnidiospores, which are spread by rain splash to neighboring plants, causing secondary infections.
4. Symptom Development:
Infected plants develop characteristic symptoms on leaves, stems, and pods, leading to reduced photosynthetic capacity, girdling of stems, and pod and seed infection.
5. Disease Spread:
The cycle of spore production, dispersal, and infection continues throughout the growing season, particularly under favorable environmental conditions.
Management
1. Cultural Practices:
Crop Rotation: Practice crop rotation with nonhost crops (at least 3 years) to reduce the buildup of Ascochyta inoculum in the soil.
Sanitation: Remove and destroy crop residues and volunteer plants that can harbor the pathogen to minimize the source of primary inoculum.
Resistant Varieties: Use resistant or tolerant chickpea varieties. Breeding efforts continue to improve resistance to Ascochyta blight.
Proper Spacing: Maintain adequate plant spacing to enhance air circulation and reduce leaf wetness duration.
2. Chemical Control:
Seed Treatment: Treat seeds with fungicides such as thiram or captan before planting to reduce seedborne inoculum.
Foliar Fungicides: Apply foliar fungicides such as chlorothalonil, mancozeb, azoxystrobin, and pyraclostrobin at the first sign of disease and continue applications based on weather conditions and disease pressure. Follow label recommendations for application rates and intervals.
Fungicide Resistance Management: Rotate fungicides with different modes of action to prevent the development of fungicideresistant strains of Ascochyta rabiei.
3. Biological Control:
Biocontrol Agents: Research and use of biocontrol agents such as Bacillus subtilis and Trichoderma spp. are being explored for their effectiveness against Ascochyta blight.
4. Environmental Management:
Irrigation Practices: Use drip irrigation instead of overhead irrigation to minimize leaf wetness. Water early in the day to allow foliage to dry before nightfall.
Weather Monitoring: Implement disease forecasting systems based on weather conditions to time fungicide applications more effectively.
By integrating these management strategies, the impact of Ascochyta blight on chickpea crops can be minimized, ensuring healthier plants and higher yields.