Alternaria is a genus of ascomycete fungi. Alternaria species are known as major plant pathogens. There are 299 species in the genus they are ubiquitous in the environment and are a natural portion of fungal flora almost everywhere. The club shaped spores are single or form long chains. So Main objective of this investigation is to isolate different Alternaria species from different portions of plant and diagnosed their species. They are standard agents of decay and decomposition. At least 20% of agricultural spoilage is triggered by Alternaria species not all Alternaria species are pests and pathogens; some have listed promise as biocontrol agents against invasive plant species. The genus is now known to be polyphyletic. Alternaria alternate generates early blight of potato, leaf spot disease in Withania somnifera and can infest several alternative plants. Alternaria abrorescens generates stem cancer of tomato, Alternaria arbsti causes Leaf lesions on Asian pear, Alternaria blumeae generates cessions on Blumea aurita, Alternaria brassicae infests numerous vegetables and roses. Alternaria carotiinculate generates leaf blight on corrot, Alternaria citri generates black rot on citrus plants. Alternaria cucumerina grows on multiple cucurbits, Alternaria infectoria infests Wheat, Alternaria solani generates early blight in potatoes and tomatoes. Alternaria toxins are mycotoxins fabricated by Alternaria species. The genus Alternaria currently encompasses around 50 species. At the cellular level. Toxins are fabricated by AAL that are necessary for pathogenicity on tomato. The fungus lives in seeds and seedlings and is also spread by spores. The disease flourishes in dead plants that have been left in dead plants that have been left in gardens over winter. There are no insect vectors for this disease.