Rhizopus is not limited to fruit. It is a highly contagious fungus that can grow even in a refrigerator if food items are not kept covered. Initially the infection begins on one piece of fruit. The fruit quickly becomes covered in sporangia, which eventually rupture, releasing their spores into the air. Any uncovered food in the refrigerator is then vulnerable to contamination by the spores. Green fruit has a better chance of survival since it is inherently more resistant to the disease.