Black bread mold

Rhizopus stolonifer

1. Identification

Rhizopus stolonifer (Ehrenb.) Vuill. is a saprophytic and opportunistic pathogenic fungus widely distributed in agricultural and postharvest environments. It is responsible for rapid and aggressive soft rots in fruits and vegetables, especially under high humidity conditions. This species is one of the main causes of postharvest losses in fresh produce.

2. Causal agent

Zygomycete fungus, order Mucorales, family Rhizopodaceae, genus Rhizopus. It is characterised by coenocytic hyphae, stolons, rhizoids and black sporangia containing sporangiospores. It exhibits very fast growth and a high capacity to colonise wounded or weakened tissues.

3. Main hosts

• Fruit crops: strawberry, raspberry, blackberry, grape, fig
• Vegetable crops: tomato, pepper, sweet potato, carrot
• Climacteric fruits: peach, plum, mango
• Stored products: bread, farinaceous products
• Various postharvest commodities with wounds or excess moisture

4. Symptoms

Symptoms begin as water‑soaked, softened areas that rapidly progress to watery rot. The surface of infected tissue develops white mycelium, which later forms black structures corresponding to sporangia. Disease progression is extremely fast, leading to complete collapse of the fruit or vegetable. In postharvest conditions, the disease is favoured by wounds, high humidity and moderate temperatures.

5. Disease cycle

Rhizopus stolonifer survives in plant debris, soil, contaminated surfaces and storage structures.

Dispersal:

• Sporangiospores carried by air
• Spread through contact between fruits
• Spread via contaminated boxes, tools and surfaces

Infection:

• Favoured by wounds and weakened tissues
• Occurs in mature fruits and postharvest vegetables
• High humidity accelerates germination and colonisation

Polycyclic cycle:

• Multiple rapid infections, with explosive growth under favourable conditions

6. Favourable conditions

Development of Rhizopus stolonifer is favoured by moderate to high temperatures, high humidity, poor ventilation and the presence of wounds on fruits. Storage environments with poor hygiene or condensation significantly increase disease incidence. Progression is extremely rapid and can destroy entire lots within hours.

7. Disease management

Management focuses on reducing humidity, improving ventilation and careful handling of fruits to avoid wounds. Strict hygiene of boxes, storage rooms and surfaces is essential. Refrigeration slows fungal development. Biological control may be applied with authorised antagonists. Chemical control must follow local regulations and be used only when permitted.

References

• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• EPPO – Diagnostic Protocols for Rhizopus spp.
• FAO – Postharvest Disease Management Guidelines.
• Pitt, J.I., & Hocking, A.D. (2009). Fungi and Food Spoilage.