A) Rust of Lentil

Causal Organism (Etiology):

• Pathogen: Uromyces fabae
• Sub-division: Basidiomycotina
• Nature: Fungus causing rust pustules on leaves, leading to reduced photosynthesis and yield loss.

Symptoms:

• Leaf Symptoms:
  • Small, circular urediosori appear on both leaf surfaces, initially light brown turning to dark brown or black.
  • Pustules are surrounded by a yellow halo, giving a characteristic rust appearance.
  • In severe infections, pustules merge, causing extensive leaf damage.
  • Premature defoliation and reduced photosynthetic activity occur due to heavy infection.
• Other Symptoms:
  • Stem and pod infections can also occur, but are less common.
  • Stunted growth and poor pod formation in severely affected plants.

Disease Cycle:

• Primary Infection: Occurs through urediospores and teliospores present on alternate hosts like bean, pea, and vetch. Pathogen overwinters as teliospores in the soil or on crop debris.
• Secondary Infection: Spread through aeciospores which are wind-borne and infect healthy plants.
• Survival: Teliospores persist in plant debris, serving as a source of primary inoculum for the next crop season.

Favourable Conditions: Temperature and Humidity: Cool temperatures (15-20°C) and high humidity favour spore germination and infection. Dew on leaf surfaces promotes the development of rust pustules.

Management:

• Cultural Practices:
  • Remove infected plants and destroy plant debris to reduce primary inoculum.
  • Practice crop rotation with non-host crops like cereals to break the disease cycle.
• Chemical Control:
  • Spray fungicides like Mancozeb (0.2%) or Chlorothalonil (0.2%) at the initial appearance of symptoms.
  • Repeat application at 10-15 day intervals under favourable conditions.
• Resistant Varieties: Grow rust-resistant varieties to minimize disease impact.
• Field Hygiene: Ensure proper plant spacing to improve air circulation and reduce leaf wetness. Avoid overhead irrigation to limit favourable conditions for rust development.

B) Wilt of Lentil

Causal Organism (Etiology):

• Pathogen: Fusarium oxysporum f.sp. lentis
• Sub-division: Deuteromycotina
• Nature: Soil-borne fungus causing vascular wilt and plant death.

Symptoms:

• Seedling Stage: Sudden drooping of seedlings followed by drying of leaves and seedling death. Vascular discoloration is visible when the stem is split open.
• Adult Stage:
  • Symptoms appear from flowering to late pod-filling stages.
  • Top leaflets droop suddenly, with leaflet closure without premature shedding.
  • Dull green foliage followed by wilting of the whole plant or individual branches.
  • Stunted growth and poor pod formation in severely affected plants.
• Root Symptoms: Brown discolouration of vascular tissues in the root and lower stem. Root decay and poor nutrient uptake leading to plant death.

Disease Cycle:

• Primary Infection: Occurs from dormant hyphae and chlamydospores present in the soil. Pathogen enters through roots and colonizes vascular tissues, blocking water and nutrient flow.
• Secondary Infection: Spread by conidia and chlamydospores through irrigation water, soil movement, and farm tools.
• Survival: Chlamydospores can survive in soil for several years, even in the absence of the host plant.

Favourable Conditions:

• Temperature and Soil Moisture:
  • Soil temperatures of 23° to 27°C favour disease development.
  • Moist soils with poor drainage increase root infection and spread.

Management:

• Seed Treatment: Treat seeds with Carboxin + Thiram (Vitavax power) @ 2 g/kg to reduce seed-borne inoculum.
• Cultural Practices: Crop rotation with non-host crops like cereals to break the disease cycle. Deep summer ploughing to expose and kill dormant spores in the soil.
• Sanitation and Hygiene: Remove and burn infected plant debris after harvest. Maintain field hygiene by disinfecting tools and equipment.
• Resistant Varieties: Grow wilt-resistant cultivars to minimize crop loss.
• Soil Amendments: Application of organic matter and balanced fertilization to enhance plant vigour and disease resistance.
• Biological Control: Use of biocontrol agents like Trichoderma spp. and Pseudomonas fluorescens for soil treatment.