Filamentous fungi produce various sorts of secondary metabolites during their active growth and reproduction. Mycotoxins produced by fungal genera have particular significance that causes cell death and damages leading to disease development. This book investigates the phytotoxic effect of metabolites produced by phytopathogenic fungus Alternaria alternata. The fungal genus Alternaria encompasses severe pathogenic species causing diseases to various economically important horticultural crops and vegetables. This book provides valuable knowledge about the fungal toxins isolated from Alternaria species, their isolation, and characterization by various chromatography techniques, which will help in understanding the process of disease development during adverse conditions. Fungal toxins is an invaluable resources for researchers, academic institutions and professionals working in the area of fungal toxins and bio-molecules and their applications for developing disease resistant plants and drug development. Nowadays, these toxins are used as probes for rapid screening of plant clones or the progeny from crosses for development of disease resistance varieties of plants.