Blue mold

Blue mold, caused by the fungus Penicillium expansum, is a significant postharvest pathogen belonging to the class Eurotiomycetes. It is one of the most destructive fungi affecting fruit and vegetable quality during transit and storage. This mold acts as a necrotrophic pathogen, actively invading plant tissues and causing rapid structural breakdown.

The primary hosts of this fungus are pome fruits, particularly apples and pears, although it can infect a wide range of other crops. The disease manifests as soft, light-brown, water-soaked lesions that eventually become covered with dense, powdery, blue-green conidial masses. Infection occurs through wounds, stem punctures, and skin abrasions sustained during the harvesting or packing process.

The lifecycle of Penicillium expansum is driven by the production of vast quantities of airborne conidia. Once introduced into a storage facility, these spores can contaminate equipment, walls, and the fruit surface itself. The fungus survives as spores or dormant mycelium on plant debris or in soil, making it a persistent threat in any agricultural environment that lacks strict sanitation.

Environmental conditions play a critical role in the severity of blue mold outbreaks. While the fungus thrives in warm, humid conditions, it remains psychrotolerant, meaning it can continue to colonize host tissues even at temperatures close to 0°C. This ability to withstand cold storage environments makes it particularly difficult to manage in commercial fruit production chains.

The pathogenicity of this fungus leads to severe economic losses and food safety risks due to the production of the mycotoxin patulin. Management requires an integrated approach to maintain product integrity:

• Implementation of strictly controlled atmosphere storage
• Thorough sanitation of storage facilities and harvesting tools
• Minimization of mechanical damage during harvest
• Postharvest application of approved chemical fungicides
• Effective sorting to prevent the spread of decay within bins