Pseudomonas cattleya

Taxonomic position and nature of the pathogen. The bacterium Pseudomonas cattleya (often classified as Acidovorax cattleyae) belongs to the family Comamonadaceae. It is a gram-negative rod-shaped bacterium known primarily as a specialized phytopathogen that targets orchids, causing severe bacterial leaf spot and brown rot.

Diseases and host crops. This pathogen is the causative agent of bacterial brown rot, primarily affecting orchid genera such as Cattleya, Phalaenopsis, and Dendrobium. The disease manifests as water-soaked, translucent spots on the leaves, which quickly enlarge, become necrotic, and turn dark brown or black, often accompanied by a foul odor due to tissue liquefaction.

Biology and life cycle. The pathogen typically enters the plant through wounds, natural openings (stomata), or insect feeding sites. Once inside the plant tissue, the bacteria multiply rapidly within the intercellular spaces, secreting enzymes that degrade cell walls. The infection is disseminated primarily through water splashes, contaminated tools, and infected nursery stock.

Conditions for development and harmfulness. High humidity levels exceeding 80% and temperatures between 25°C and 30°C are optimal for the rapid colonization of host tissues. The bacteria are highly contagious and can cause total plant death in as little as 48 to 72 hours, especially when the disease reaches the crown or the stem base of the orchid.

Measures for protection and control. Successful management requires a focus on sanitation and environment modification:

• Provide optimal airflow around the plants to ensure foliage dries quickly after irrigation.
• Strictly sanitize all cutting tools using 70% alcohol or specialized disinfectants between every plant.
• Immediately isolate symptomatic plants and remove diseased tissue with a sterilized blade.
• Apply copper-based bactericides or specialized antimicrobial agents to the affected areas as a prophylactic or corrective treatment.