Bacterial canker

Pseudomonas syringae, Pseudomonas morsprunorum

Pathogen: Pseudomonas syringae is a Gram-negative bacterium that encompasses various pathovars (pathogenic varieties) capable of infecting a wide range of plant species. Different pathovars of Pseudomonas syringae are associated with specific diseases in various plants.

Common Pathovars:

  1. Pseudomonas syringae pv. syringae:

    • Causes Bacterial Brown Spot: Affects a variety of plants, causing water-soaked lesions on leaves and stems.

  2. Pseudomonas syringae pv. tomato:

    • Causes Bacterial Speck and Spot of Tomato: Affects tomato plants, leading to specks on leaves and spots on fruits.

  3. Pseudomonas syringae pv. phaseolicola:

    • Causes Halo Blight of Beans: Affects beans, causing water-soaked lesions with a halo-like appearance.

Symptoms:

  • Lesions: Symptoms often include water-soaked lesions on leaves, stems, and sometimes fruits.
  • Discoloration: Lesions may progress to brown or black discoloration.
  • Halo Effect: Some pathovars cause a characteristic halo effect around lesions.

Conditions Favoring Disease:

  1. Warm and Wet Conditions: Pseudomonas syringae thrives in warm and humid environments.
  2. Rain or Irrigation: Moisture on leaves and stems from rain or irrigation facilitates bacterial spread.

Management:

  1. Cultural Practices:

    • Sanitation: Remove and destroy infected plant material to reduce the source of inoculum.
    • Crop Rotation: Rotate crops to prevent the buildup of bacteria in the soil.

  2. Bactericides:

    • Copper-Based Bactericides: Application of copper-based bactericides can help control bacterial diseases.

  3. Avoid Overhead Irrigation:

    • Drip Irrigation: Use drip irrigation instead of overhead sprinklers to minimize leaf wetness.

  4. Resistant Varieties:

    • Plant Resistant Cultivars: Choose plant varieties that are resistant or less susceptible to the specific pathovar causing the disease.

Note: Different pathovars of Pseudomonas syringae have specific host ranges, and their impact varies. Management strategies may need to be tailored based on the specific pathovar and the affected crop.

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