Loose smut of wheat
C/O: ustilago nuda tritici
Symptoms:
- Appear only after emergence of the ears.
- Every ear of the affected plants is converted into a black mass of spores and no grains are formed.
- The infected heads emerge from the boot leaf one to three days earlier than those of healthy plants.
- All parts of the spikelets convert into smut spores except awn.
- Initially smut sori, covered with thin silvery membrane.
- Later, at emergence, the membrane breaks and spores liberated in atmosphere.
- All of the floral parts of the head, except for the rachis and pericarp membrane, are invaded by mycelium of the fungus and converted into loose aggregates of smut spores (teliospores)
Pathogen:
- Chlamydospores/teliospore of the fungus are pale, olive brown, spherical to oval in shape.
Favourable condition:
- Infections occur only during flowering
- Favored by wet weather and high humidity.
- Cool to moderate temperatures (16-22°C).
Survival and spread:
- Internal Seed born disease
- Primary source of infection: infected seeds.
- Secondary source of infection: smutted spores/teliospore dispersed by wind, water or insects.
Disease cycle:
- Systemic infection.
- Monocyclic disease
Management:
- Grow resistant varieties kalyanasona, PV 18, WG 307 and HD 450.
- Hot water treatment (Jensen, 1908): Soak the seed in cold water for 4 hours and then immerse the seed in hot water at a temperature of 520C for about 10 minutes. Dry the seed in shade before sowing.
- Solar seed treatment (Luthra and Sattar, 1934): Soak the seed in water for 4 hours (8 AM to 12 Noon) and expose the seed to the hot sun for 4 to 5 hours (from 12 Noon to 5 PM) on cement or rocky surface. This can be practiced in the areas where the summer temperatures are high (42-440C).
- Anaerobic seed treatment (USA): Soak the seeds for 2-4 hours in water between 15-200C and keep the moist seeds in air tight containers for 65-70 hours and there after dry the seed.
- Seed treatment with systemic chemicals like vitavax@0.2% or Benlate@0.2%.