Bacterial blotch of mushrooms

Pseudomonas tolaasii is a soil-borne bacterium that causes bacterial blotch, a destructive disease affecting cultivated mushrooms. This pathogen is a significant concern for the mushroom industry worldwide, as it can cause rapid spoilage of crops shortly before harvest, leading to substantial financial losses for growers.

The primary host for this bacterium is the common mushroom, Agaricus bisporus. P. tolaasii does not typically infect the mycelium directly but targets the fruit bodies. It colonizes the surface of the mushroom cap and produces a toxin called tolaasin, which degrades cell membranes and results in localized tissue death and discoloration.

The characteristic symptoms include the appearance of yellow to dark brown, slightly sunken spots on the mushroom caps. In advanced stages, these spots may spread, turning into a slimy, dark rot with a distinct odor. The severity of the symptoms depends on the population density of the bacteria and the physiological state of the mushrooms.

Environmental conditions are the main drivers of disease outbreaks. High relative humidity and the presence of a water film on the mushroom caps are critical for the motility and spread of the bacteria. Poor ventilation in mushroom houses prevents the caps from drying, providing the perfect environment for the pathogen to thrive.

• Implement strict hygiene protocols for workers and equipment.
• Maintain optimal relative humidity (below 85-90%) to prevent condensation.
• Ensure adequate air circulation to dry mushroom caps quickly after watering.
• Use high-quality, pasteurized casing soil to prevent initial contamination.
• Regularly monitor the crop and immediately remove any infected mushrooms.