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📈 Diseases of Wheat — Rusts

Diseases of Wheat — Rusts.

Rusts are the most devastating group of diseases affecting wheat (Triticum aestivum) globally. Three types of rust attack wheat, each caused by a different species of Puccinia. Collectively, they can cause yield losses of 10-100% in epidemic years.

Overview of Wheat Rusts

Feature Black/Stem Rust Brown/Leaf Rust Yellow/Stripe Rust
Pathogen Puccinia graminis tritici Puccinia triticina Puccinia striiformis
Pustule colour Dark reddish-brown to black Orange-brown Yellow
Pustule location Stems, leaf sheaths, glumes Leaves (upper surface) Leaves (in stripes along veins)
Telial stage Black, on stems Dark brown, on leaf underside Dark brown, rare in India
Alternate host Berberis vulgaris Thalictrum spp. Berberis spp.
Optimal temp 20-25 degrees C 15-22 degrees C 10-15 degrees C

Black Stem Rust (Puccinia graminis tritici)

Symptoms

  • Uredial stage: Elongated reddish-brown pustules (uredia) on stems, leaf sheaths, and occasionally leaves
  • Pustules burst through the epidermis giving a rough, torn appearance
  • Telial stage: Dark brown to black teleutosori appear late in the season
  • Severe infections cause weakened stems, lodging, and shrivelled grains

Disease Cycle

The fungus is heteroecious (requires two hosts) and macrocyclic (five spore stages). Uredospores are the primary repeating stage on wheat. In India, uredospores survive on self-sown wheat in the Nilgiri and Palani hills (southern India) and are carried northward by winds.

Management

  • Grow resistant varieties (e.g., varieties with Sr31, Sr38 genes)
  • Eradication of Berberis (alternate host) near wheat fields
  • Timely sowing to escape peak infection period
  • Foliar spray of Propiconazole 25 EC (0.1%) at first appearance

Brown Leaf Rust (Puccinia triticina)

Symptoms

  • Small, circular, orange-brown pustules scattered irregularly on the upper leaf surface
  • Telia appear as dark brown spots on leaf undersides late in the season
  • Heavy infections cause premature leaf drying and reduced grain filling

Favorable Conditions

  • Moderate temperatures (15-22 degrees C) with intermittent rains
  • Most prevalent in the central and peninsular zones of India

Management

  • Resistant varieties with Lr genes (Lr24, Lr28, Lr34)
  • Avoid late-sown conditions
  • Spray Mancozeb 75 WP (0.25%) or Propiconazole

Yellow Stripe Rust (Puccinia striiformis)

Symptoms

  • Yellow uredial pustules arranged in linear rows between leaf veins, giving a striped appearance
  • Also affects ears and glumes
  • Causes severe shrivelling of grains under cool conditions

Favorable Conditions

  • Cool temperatures (10-15 degrees C) — most active during December-February in the northern plains
  • High humidity and cloud cover

Management

  • Deploy varieties with Yr genes (Yr15, Yr18)
  • Early sowing to ensure crop maturity before peak cool weather
  • Chemical control with Tebuconazole or Propiconazole

Understanding the biology and epidemiology of wheat rusts is critical for timely surveillance and management, as rust epidemics can develop rapidly under favorable weather conditions.

Summary Cheat Sheet

Rust type Pathogen Optimum condition
Stem rust Puccinia graminis tritici Warm and humid period
Leaf rust Puccinia triticina Moderate temperature with intermittent rain
Stripe rust Puccinia striiformis Cool weather in northern plains

References

1 source

- Wheat rust surveillance notes (ICAR). - Agrios GN. Plant Pathology. 5th ed. - Cereal pathology lecture compendiums.

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