Mouldy apple. Commercially grown apples are covered with a layer of wax that protects the fruit from infection. If this protective layer is damaged, fungi may cause the apple to go mouldy. Here, Sclerotinia brown rot has infected the central apple. The fungus has secreted digestive enzymes, breaking down the apple's tissues to obtain nutrients for the growth of the fungus, turning the apple brown. Concentric rings of spore-producing pustules have developed as the mould extends outwards from the initial point of infection. When these contact neighbouring fruits, the infection may spread.