Blue mold

The causative agent of the disease is the fungus Penicillium expansum. It is a filamentous fungus belonging to the Ascomycota division, widely known for causing postharvest rot in various fruit crops. It represents a significant economic threat to the fruit storage industry globally.

Primary hosts for this pathogen include pome fruits such as apples and pears. However, the fungus is not limited to these crops and can affect stone fruits, grapes, citrus, and various vegetables when they are kept in storage conditions that facilitate fungal growth and spread.

Symptoms typically manifest as soft, water-soaked, tan or brown lesions on the surface of the fruit. Over time, the affected area becomes covered in a distinct blue-green, powdery sporulation layer. In advanced stages, the fruit produces a characteristic musty odor, rendering it completely unmarketable and inedible due to tissue collapse.

The development of Penicillium expansum is favored by high relative humidity and moderate temperatures. The fungus acts as a wound pathogen, entering fruit primarily through mechanical injuries, bruises, or stem punctures. Once inside, the fungus secretes enzymes that break down cell walls, facilitating rapid colonization of the healthy tissue.

Economic damage is twofold: direct loss of fruit and the accumulation of patulin, a toxic secondary metabolite that poses health risks to consumers. Control strategies focus on sanitation:

• Rigorous disinfection of storage facilities and wooden bins.
• Handling fruit carefully to minimize bruises and cuts.
• Maintaining cold chain integrity throughout storage and transport.
• Applying recommended postharvest fungicides where permitted.