Bacterial blotch of mushrooms

Affected areas often become sticky or slimy to the touch, which is a characteristic symptom of bacterial infection. In advanced cases, the spots merge, covering the entire surface of the cap.

Deformation of the caps in young fruiting bodies can occur during active growth, leading to stunted development and a decrease in product quality.

Unlike fungal infections, bacterial blotch does not show visible mycelial growth or spore production. The affected mushroom tissue softens rapidly and emits an unpleasant, putrid odor.

Sometimes the infection affects only the top epidermis of the cap, but in high humidity, it penetrates deep into the flesh, making the mushroom unfit for consumption.

The causative agent of the disease is the Gram-negative bacterium Pseudomonas agarici, which belongs to the group of phytopathogenic pseudomonads.

This is an obligate parasite specializing in attacking the fruiting bodies of various cultivated mushrooms, most commonly the button mushroom (Agaricus bisporus).

These bacteria have a high capacity for rapid reproduction in high-humidity conditions, actively using the organic matter of the mushroom tissue for their metabolism.

The microorganism is easily transmitted through water droplets, personnel tools, and can be carried by mushroom flies or mites living in cultivation rooms.

The pathogen's genetic plasticity allows it to adapt to the microclimate of growing chambers, forming stable reservoirs in wall cracks and shelving units.

The key factor for disease development is excessive air humidity and surface moisture on the mushrooms, which remains above 90% for extended periods.

A temperature range of 18–22°C is considered optimal for the active growth and spread of Pseudomonas agarici, often coinciding with the fruiting stages.

A lack of high-quality ventilation, which should facilitate rapid evaporation of moisture from cap surfaces, creates ideal conditions for pathogen colonization.

Stagnant air inside the growing chambers leads to the accumulation of condensation, which serves as the main vector for bacterial spread between neighboring mushrooms.

Poor sanitation practices, the presence of organic debris, and rotting mushrooms in the room provoke outbreaks and increase the infectious pressure.

The primary damage lies in a sharp decline in the product's market appearance, causing mushrooms to lose value and become unmarketable.

In cases of massive bacteriosis, crop losses can reach significant volumes, as infected fruiting bodies break down quickly and must be discarded.

The disease negatively impacts the reputation of the mushroom farm, as spotted mushrooms cannot be sold through retail distribution networks.

Beyond direct crop loss, the pathogen creates additional costs for sanitation and facility cleaning, which increases overall production costs.

Severe infestation may require a complete shutdown of the growing cycle for unscheduled decontamination, causing equipment downtime and financial losses.

The foundation of protection is strict adherence to humidity regulations and ensuring active airflow to dry the caps quickly after watering.

Regular disinfection of tools, equipment, and facilities with agents effective against Gram-negative bacteria reduces the risk of infection.

It is essential to promptly remove infected fruiting bodies from the chambers to prevent them from decomposing, which acts as a source of secondary infection.

Managing planting density and controlling the quality of the casing material prevents the creation of favorable environments for bacterial outbreaks.

Implementing strict sanitary protocols for personnel working in the growing area prevents the introduction of the pathogen from outside and its spread within the production block.