Disease of Gram

A) Wilt of Gram

Causal Organism (Etiology):

• Pathogen: Fusarium oxysporum f.sp. ciceri
• Sub-division: Deuteromycotina
• Nature: Soil-borne fungus that infects the vascular system, causing blockage and wilting.

Symptoms:

• Field Symptoms:
  • Wilting and death of seedlings or adult plants in patches.
  • Drooping of petioles, rachis, and leaflets, followed by sudden death.
  • Leaves turn yellow, then light brown, and droop prematurely.
  • Vascular Discoloration:
    • Brown discoloration of the vascular bundles observed on longitudinal splitting of the stem.
  • Partial Wilt: Sometimes only a few branches are affected.

Disease Cycle:

• Primary Infection: Through chlamydospores in the soil, which remain viable until the next crop season.
• Secondary Infection: Spread through irrigation water, cultural operations, and contaminated farm implements.
• Survival: The pathogen survives as chlamydospores in soil and infected plant debris.

Favourable Conditions:

• High soil temperature (Above 25°C).
• High soil moisture.
• Monocropping of chickpea.
• Presence of weed hosts like:
  • Cyperus rotundus (Nutgrass).
  • Tribulus terrestris (Puncture vine).
  • Convolvulus arvensis (Field bindweed).

Management:

• Seed Treatment: Carboxin + Thiram (Vitavax power) at 2 g/kg of seed. Trichoderma viride at 4 g/kg or Pseudomonas fluorescens @ 10 g/kg of seed.
• Cultural Practices:
  • Apply heavy doses of organic manure or green manure to improve soil health.
  • Follow 6-year crop rotation with non-host crops to break the disease cycle.
  • Remove and destroy infected plant debris to reduce inoculum.
• Resistant Varieties: Use resistant cultivars like JG 74, Pusa 256, and ICCC 37.

B) Grey Mould of Gram

Causal Organism (Etiology):

• Pathogen: Botrytis cinerea
• Sub-division: Deuteromycotina
• Nature: Air and soil-borne fungus that causes rot and decay in above-ground plant parts.

Symptoms:

• Initial Symptoms: Soft rot at the base of the stem in the collar region. Affected tissues are covered with fluffy grey mould.
• Disease Progression:
  • Affected plants wither and die.
  • Small black sclerotia form on the surface of affected tissues once the plant dies.
  • In older plants, sometimes only a few branches are affected, while the rest appear normal.
• Seedling Infection: Causes damping-off and thinning of the crop stand.
• Pod Infection: Infected pods become shriveled and fail to produce healthy seeds.

Disease Cycle:

• Primary Infection: Fungus survives on infected seed, decaying plant debris, and as soil-borne sclerotia.
• Secondary Infection: Spread through air currents carrying fungal spores, leading to rapid disease spread.
• Survival: Survives as sclerotia in the soil or on crop residues.

Favourable Conditions:

High humidity and cool temperatures (15-20°C).

• Dense crop canopy and poor air circulation.
• High soil moisture and continuous cropping of chickpea.
• Presence of dead or decaying plant matter.

Management:

• Seed Treatment: Carboxin + Thiram (Vitavax power) at 2 g/kg of seed. Trichoderma viride at 4 g/kg or Pseudomonas fluorescens @ 10 g/kg of seed.
• Fungicidal Sprays: Spraying Carbendazim @ 0.1% or Mancozeb @ 0.2% at the flowering stage.
• Cultural Practices:
  • Apply heavy doses of organic manure or green manure.
  • Follow 6-year crop rotation with non-host crops.
  • Remove and destroy crop residues after harvest to reduce inoculum.
  • Maintain optimum plant spacing for better air circulation.
• Resistant Varieties: Use resistant cultivars like BG 212, ICCV 10, and JG 74.

C) Ascochyta Blight of Gram

Causal Organism (Etiology):

• Pathogen: Ascochyta rabiei
• Sub-division: Deuteromycotina
• Nature: Fungus causing necrotic lesions on leaves, stems, and pods.

Symptoms:

• Timing: Disease typically appears during flowering and podding stages. Visible as patches of blighted plants in the field.
• Leaf Symptoms:
  • Small, water-soaked necrotic spots that enlarge rapidly under favourable conditions.
  • Lesions:
    • Round or elongated with grey centers surrounded by a brownish margin.
    • These lesions may coalesce, leading to blighting and drying of leaves.
• Stem and Pod Symptoms:
  • Similar spots appear on stems and pods.
  • Lesions on stems can cause girdling, leading to drying and breaking of the stem.
  • Infected pods show sunken lesions, leading to seed discoloration and shriveling.

Disease Cycle:

• Primary Infection: Seed-borne pycnidia and infected plant debris in the soil act as the primary sources of inoculum. Fungus can survive in seed coats and on crop residues from previous seasons.
• Secondary Infection: Air-borne conidia spread the disease within and between fields. Conidia are dispersed by wind and rain splashes.
• Survival: Survives on infected seeds and crop residues as pycnidia and mycelium.

Favourable Conditions:

• Temperature and Humidity:
  • Night temperatures of 10°C and day temperatures of 20°C.
  • Rains accompanied by cloudy weather enhance spore germination and infection.
• Canopy Density: Excessive canopy and poor air circulation create high humidity, favouring disease development.
• Prolonged Leaf Wetness: Continuous leaf wetness for 24-48 hours enhances spore germination.

Management:

• Cultural Practices: Remove and destroy infected plant debris in the field to reduce the inoculum source. Follow crop rotation with cereals to break the disease cycle.
• Seed Treatment: Treat seeds with Carboxin + Thiram (Vitavax power) to eliminate seed-borne inoculum.
• Fungicidal Sprays: Carbendazim @ 0.1% or Chlorothalonil @ 0.3% during early flowering and podding stages. Repeat sprays at 10-15 day intervals under conducive weather conditions.
• Resistant Varieties: Use resistant cultivars like ICCV 05530, ICCV 10, and JG 74.
• Field Hygiene: Avoid dense planting to improve air circulation and reduce humidity. Proper irrigation management to avoid prolonged leaf wetness.