Rhizopus sp., probably R. stolonifer (Ehr. ex Fr.) Lind.
Rhizopus rot is seen occasionally on apples and pears on the market, but always on fruits that have been weakened in some way, as for example, by overmaturity or freezing injury. Affected tissues are soft and watery and have a sour smell.
Rhizopus is a fungus that occurs widely in nature. It is distributed both by contact and by means of its spores. It can be distinguished from blue mold (Penicillium expansum) and gray mold (Botrytis cinerea) by its dark-colored, coarse mold if present and by the gray salt-and-pepper appearance resulting from the young (white) and mature (black) fruiting bodies.
Rhizopus rot is not likely to occur on pome fruits if they have been handled carefully throughout the processes of picking, packing, and transporting to market. If it becomes established, it can be controlled by keeping the fruit temperature below 40 °F.