Pseudomonas cichorii

Systematic position and type of pathogen: Pseudomonas cichorii is a Gram-negative aerobic bacterium belonging to the genus Pseudomonas. It is a significant phytopathogen known for its ability to cause severe bacterial diseases across a wide range of horticultural and ornamental plant species. It is widely recognized for its opportunistic nature in environments with high humidity.

Diseases and host plants: This pathogen causes various diseases, primarily bacterial spots, blights, and rots. Key host plants include lettuce, endive (chicory), tomato, cucumber, as well as popular ornamentals like chrysanthemums, geraniums, and petunias. Infection is typically characterized by water-soaked lesions that turn necrotic, dark brown, or black, often with yellow halos around the affected tissue.

Biology and life cycle: The bacterium survives in crop debris, contaminated soil, and alternative weed hosts. Transmission occurs primarily via water splashing (rain or overhead irrigation), contaminated equipment, and physical contact between plants. Once the bacteria enter the host through natural openings or wounds, they multiply rapidly, leading to the destruction of parenchymal tissues and systemic spread within the plant.

Development conditions and impact: The optimal conditions for disease development include high humidity, moderate temperatures (20–28°C), and frequent rainfall. In greenhouse environments, poor ventilation and high plant density significantly increase the risk of an outbreak. The economic impact is substantial, as infected crops are often rendered unsalable due to disfigurement, and severe infestations can lead to total crop failure.

Protection and control measures: Effective management requires an integrated approach. Important strategies include using disease-free starting material, practicing crop rotation, and ensuring proper sanitation of tools. It is crucial to manage humidity levels and avoid overhead irrigation to minimize bacterial spread. Copper-based bactericides may provide some control, but they are most effective as a preventive measure rather than a curative treatment.