Citrus blue mold

Penicillium ulaiense is a pathogenic microscopic fungus that serves as a major postharvest agent causing significant decay in citrus fruits. Belonging to the class of imperfect fungi, this species specializes in infecting citrus crops during storage and transit, leading to rapid deterioration of fruit quality.

The primary hosts of this pathogen include various Citrus species such as lemons, oranges, mandarins, and grapefruits. The fungus primarily attacks fruits after harvest, significantly reducing their marketability and often leading to total loss of fruit batches if left unchecked in storage facilities.

Initial infection symptoms appear as soft, water-soaked spots that rapidly enlarge. Shortly after, a thick grayish-blue mold layer develops on the fruit surface, consisting of the fungus's conidiophores. Unlike other Penicillium species, P. ulaiense often forms distinct concentric rings and exhibits high sporulation rates on the affected fruit surface.

Infection development is highly favored by high relative humidity (above 85-90%) and moderate temperatures ranging from 15°C to 25°C. The primary infection source is fungal spores, which are easily disseminated by air currents and settle on mechanical injuries of the peel, such as cracks, scratches, or stem-end detachment sites.

The economic impact of this pathogen lies in its ability to cause "nesting" or clusters of decay within storage crates, which can spread the disease to healthy fruits. To prevent epidemics, the following management strategies are crucial:

• Rigorous disinfection of storage facilities and shipping containers before harvest placement.
• Careful harvesting techniques to minimize mechanical damage to the fruit peel.
• Timely application of authorized postharvest fungicides to prevent spore germination.
• Maintaining strictly controlled temperature and humidity levels in cold storage to inhibit fungal growth.