Alternaria is a genus of Ascomycete fungi. Alternaria species are major plant pathogens causing disease in many crops. Alternaria species belong to the Fungi imperfecti. They do not develop asci and reproduce asexually by developing multicellular, rocket or club-shaped conidia. Alternaria species that cannot be classed as belonging to this genus, on the grounds of their sexual stadium, are no longer considered Alternaria species. Alternaria species can cause serious diseases in many crops. Seed treatment can protect seedlings against most Alternaria species. Descriptions of the relevant Alternaria species are shown below the various crops.