Rhizopus stolonifer

Rhizopus stolonifer is a microscopic fungus belonging to the Kingdom Fungi, Phylum Zygomycota, and Genus Rhizopus. Known colloquially as bread mold, it is a significant plant pathogen that causes widespread soft rot in fruits and vegetables. While it primarily acts as a saprophyte, it opportunistically infects wounded plant tissues, making it a major concern in agricultural production.

The fungus is responsible for Rhizopus soft rot, a destructive disease affecting a wide range of crops including strawberries, peaches, grapes, tomatoes, and sweet potatoes. The infection usually occurs during the ripening stage and is particularly devastating during the post-harvest period, significantly reducing the shelf life and marketability of agricultural produce.

The biology of Rhizopus stolonifer involves rapid colonization through vegetative mycelia that secrete enzymes capable of breaking down plant cell walls. A hallmark of the infection is the appearance of dense, cotton-like white mycelium that turns greyish-black as sporulation occurs. The black sporangia contain thousands of spores, which are easily disseminated by wind, water splashes, and insect vectors.

Optimal environmental conditions for the development of this pathogen include high relative humidity (above 80%) and temperatures between +20°C and +30°C. Once the fungus enters a fruit, it can cause total liquefaction of the tissue within 48 to 72 hours. The speed of growth makes it an aggressive pathogen, especially in poorly ventilated or inadequately sanitized storage facilities.

Effective management and control of Rhizopus stolonifer require an integrated strategy:

• Maintaining optimal ventilation to reduce surface moisture on crops.
• Rigorous sanitation of storage areas, packing equipment, and transport containers.
• Temperature control; cooling harvested produce promptly inhibits fungal growth.
• Careful handling of fruits to prevent mechanical injury or bruising.
• Timely removal of infected specimens to prevent spore spread within storage bins.