Rhizopus blight

Rhizopus blight is a destructive plant disease caused by the fungus Rhizopus stolonifer. Known commonly as soft rot or bread mold, this pathogen is opportunistic and highly aggressive. It quickly invades succulent plant tissues, breaking down cell walls and liquefying the infected parts, leading to total collapse of the plant material.

The fungus has a very broad host range, infecting various fruits, vegetables, and ornamentals. It is a significant issue for crops like strawberries, peaches, tomatoes, and specific greenhouse flowers such as Gerbera jamesonii. In ornamental production, the fungus can infect petals and stems, especially in high-density or high-humidity environments.

Symptoms initially appear as small, water-soaked lesions that expand rapidly. As the disease advances, a dense, cottony mass of mycelium develops, eventually turning grey or black as sporulation occurs. Infected tissues become soft, watery, and mushy, often emitting a fermented, sour odor, which makes the product completely unmarketable.

Disease progression is heavily influenced by environmental factors. High relative humidity and warm temperatures (above 20°C) are optimal for the growth and sporulation of Rhizopus stolonifer. Because the spores are airborne and easily dispersed by water or insects, the infection can spread through a crop or storage facility very quickly, potentially ruining an entire harvest in a matter of days.

Management of Rhizopus blight focuses on sanitation and environmental control rather than chemical applications alone. Since the fungus usually enters through wounds, careful handling during harvest is paramount. Effective control practices include:

• Maintaining good ventilation to reduce humidity;
• Careful harvesting to avoid mechanical injury;
• Prompt cooling of harvested produce;
• Rigorous sanitation of packing sheds and storage areas;
• Immediate removal and disposal of any infected plants or fruits.