Pseudomonas marginalis

Systematic position and nature of the pathogen. Pseudomonas marginalis is a motile, Gram-negative bacterium belonging to the genus Pseudomonas. It acts as a significant phytopathogen known for its ability to produce pectinolytic enzymes, which degrade plant cell walls. Unlike many other plant-pathogenic bacteria, P. marginalis is recognized for its psychrotrophic capabilities, meaning it can remain active and proliferate even at low, refrigerated temperatures.

Diseases and host plants. This bacterium is a primary causal agent of bacterial soft rot in a wide variety of vegetable crops, including potatoes, cabbage, carrots, onions, and tomatoes. The infection typically manifests as water-soaked lesions that rapidly expand, leading to the disintegration of plant tissues into a foul-smelling, slimy mass. The disease is particularly problematic during post-harvest storage and transport.

Biology and life cycle. The pathogen survives in the soil, on crop residues, and within infected plant debris or seeds. It enters host plants through natural openings, such as stomata or lenticels, or via mechanical wounds caused by harvesting equipment or insect feeding. Once inside the tissue, the bacteria multiply and secrete enzymes that break down the middle lamella of cell walls, allowing the infection to spread rapidly through the host plant.

Developmental conditions and impact. The development of Pseudomonas marginalis is heavily favored by high humidity and moderate to warm temperatures in the field. However, its ability to thrive at lower temperatures makes it a major concern in cold storage facilities where moisture levels are inadequately controlled. The economic impact is severe, as it causes massive crop losses during storage, rendering affected produce completely unsalable and unsuitable for processing.

Protection and control measures. Management of Pseudomonas marginalis relies on integrated agricultural practices aimed at reducing the initial inoculum and preventing secondary spread. Essential control strategies include:

• Practicing crop rotation to reduce soil-borne inoculum levels.
• Ensuring proper sanitation and disinfection of storage facilities and harvesting tools.
• Minimizing plant injury during harvesting and handling to reduce entry points for bacteria.
• Maintaining optimal ventilation and temperature control in storage units to inhibit bacterial growth.