Rhizopus arrhizus

Rhizopus arrhizus (synonym Rhizopus oryzae) is a prominent species of filamentous fungi belonging to the order Mucorales. It acts as an opportunistic phytopathogen that causes significant post-harvest and field losses. While it naturally resides in the soil as a saprophyte, it readily attacks living plant tissues, especially when they are wounded or stressed.

The primary symptom of infection is soft rot, characterized by the rapid collapse of plant tissue. It affects a wide range of commercially important crops, including tomatoes, strawberries, stone fruits, onions, and sunflowers. The fungus secretes pectinolytic enzymes that break down the middle lamella of cell walls, turning the fruit or vegetable into a soft, mushy, watery mass within a few days.

The biological cycle of this pathogen is remarkably efficient for spread. It produces millions of sporangiospores within a short period, which are easily disseminated by air currents, splashing water, or insect vectors. These spores germinate rapidly upon contact with a suitable substrate, allowing the fungus to colonize new hosts quickly, especially under favorable environmental conditions.

Environmental conditions play a crucial role in the development of Rhizopus arrhizus. The pathogen thrives in warm conditions (typically 25–35°C) and high humidity levels. Poorly ventilated storage facilities create the perfect microclimate for the fungus to transition from a single infection point to widespread crop destruction, as it spreads through direct contact between healthy and infected produce.

Effective management and control strategies rely on an integrated approach. Reducing mechanical injuries during harvesting is paramount, as the fungus requires entry points to initiate decay.

• Sanitize storage facilities thoroughly before the harvest season.
• Maintain proper ventilation and humidity control in storage.
• Sort produce to remove any symptomatic fruits immediately.
• Practice crop rotation and field sanitation to reduce soil-borne inoculum.