Rhizopus soft rot

Rhizopus soft rot, caused by the fungus Rhizopus sexualis, is a common and destructive post-harvest disease affecting a wide variety of fresh produce. As a member of the Mucorales order, this pathogen is characterized by extremely rapid colonization and the ability to macerate plant tissues through the secretion of powerful cell-wall-degrading enzymes.

This disease primarily impacts fleshy fruits and vegetables, including strawberries, tomatoes, peaches, and various stone fruits. It is widely considered a major limiting factor in the shelf life of these commodities, as it can transform healthy produce into a watery, mushy mass within a very short period of time after harvest.

The primary symptom of the infection is the rapid development of a dense, white, thread-like mycelium that covers the surface of the affected fruit. As the fungus matures, it produces numerous sporangia, giving the growth a gray or dark brown appearance. In advanced stages, the fruit loses all structural integrity, often accompanied by a fermented or yeast-like odor.

The development of Rhizopus rot is heavily favored by warm temperatures (20–30°C) and high relative humidity. The fungal spores are ubiquitous and spread easily via air currents, water splashes, and physical contact with contaminated tools or containers. Infections usually initiate through small wounds, bruises, or cracks in the fruit epidermis.

Effective management of Rhizopus rot relies on integrated disease control strategies:

• Careful handling during harvest to minimize wounds, cuts, and bruises.
• Rapid cooling of harvested produce to reduce the growth rate of the fungus.
• Strict sanitation protocols for picking bins, storage facilities, and packing equipment.
• Removal and destruction of any infected fruit to prevent spread within the storage area.

Proactive management is critical because once the disease is established, it can spread rapidly between neighboring fruits in storage boxes. By maintaining rigorous sanitary standards and optimizing post-harvest conditions, growers can significantly mitigate the impact of this aggressive pathogen on their overall yield and profitability.