Halo blight
Pseudomonas syringae pv. phaseolicola
Causal Agent:
- Bacterial Pathogen: Pseudomonas syringae pv. phaseolicola is a bacterial pathogen that causes bacterial blight in common bean plants (Phaseolus vulgaris).
2. Symptoms:
- Angular Leaf Lesions: One of the characteristic symptoms is the development of angular, water-soaked lesions on the leaves.
- Lesion Margins: Lesions often have a defined boundary between healthy and infected tissue, creating an angular appearance.
- Lesion Progression: Lesions may later turn necrotic, with a brown coloration, and can coalesce, leading to extensive damage.
3. Disease Cycle:
- Overwintering: The bacterium can survive in infected seeds and plant debris, serving as a source of inoculum for new infections.
- Infection: Pseudomonas syringae pv. phaseolicola enters plant tissues through natural openings, wounds, or stomata.
- Rain Splash and Wind: The bacterium is often disseminated through rain splash, wind-driven rain, or by contaminated farm tools.
- Favorable Conditions: Warm and humid conditions promote disease development, and the bacterium can spread rapidly during periods of high moisture.
4. Identification:
- Angular Leaf Lesions: The angular shape of lesions on leaves is a key diagnostic feature.
- Water-Soaked Appearance: Lesions may have a water-soaked appearance in the early stages of infection.
- Bacterial Streaming: Under a microscope, bacterial streaming can be observed in infected plant tissues.
5. Management:
- Resistant Varieties: Planting bean varieties with resistance to Pseudomonas syringae pv. phaseolicola is an effective strategy.
- Crop Rotation: Avoiding consecutive cultivation of beans in the same field helps reduce the pathogen's survival.
- Seed Treatment: Treating seeds with bactericides can reduce the transmission of the pathogen from seeds to seedlings.
- Copper-Based Sprays: Copper-based bactericides may be applied as a preventive measure.
6. Importance:
- Economic Impact: Bacterial blight caused by Pseudomonas syringae pv. phaseolicola can lead to reduced yields and quality of common beans.
- Global Distribution: The pathogen is found in bean-growing regions worldwide.
7. Research Significance:
- Pseudomonas syringae pv. phaseolicola has been extensively studied as a model organism for understanding the molecular basis of plant-pathogen interactions.
