The flesh of plums initially turns brown. The lesion is soft and soon collapses. As the decay development progresses, the surface of the fruit is at first covered with coarse, white spore masses, which rapidly turns black. The superficial fungal mass appears ‘whisker-like’, with interwoven structures extending outwards from the fruit, ending in black / sooty structures. Rhizopus stolonifer is the causal pathogen.
The skin and flesh of infected fruit disintegrates when touched. This phenomenon is referred to as ‘soft tissue’ rot / breakdown. Rhizopus rot is more common on mature / ripe fruit, especially when storage temperatures are elevated above 2 °C. Rhizopus rot, as well as Mucor rot, are rated as rapid growers, macerating the tissue under slightly warmer storage conditions. Like Penicillium rot, initial infections are mostly associated with injuries.