The sexual form is Diplocarpon mali Harada et Sawamura, which is called apple bivalve, and belongs to the Ascomycota fungus; the asexual form, Marssonina mali (P.Henn.) Ito. fungi. The brown spot fungus produces bacteriocin in asexual generations. It is multi-branched, 20-40 μm thick, and the cells are dark brown. Conidial discs are born above the intersections of fungal cords; the size is 108-306×45-50 μm. They break through the epidermis and are exposed after maturity. Conidiophores are colorless, solitary, cylindrical, 15 to 20 × 3 to 4 μm in size, arranged in a grid, with terminal conidia. Conidia are colorless, twin-celled, constricted in the middle, the upper cells are large and round, the lower cells are small and pointed, gourd-shaped, 14-20×5-9μm in size, containing 2-4 oil globules, and a few occasionally. Single-celled conidia are mixed together. The pseudoconidia discs are gray-white and insect-excrement-like. After absorbing water and swelling, a large number of pseudoconidia emerge and are scattered on the surface of the lesions. The ascus disk is fleshy and bowl-shaped, with a size of 105-200×80-125 μm. The ascus is broad and club-shaped, with a cap, a size of 40-49×12-14 μm, and contains 8 ascospores. Ascospores are banana-shaped, with one end slightly curved, usually with a septum, and a size of 24 to 30 × 5 to 6 μm.