Alternaria blight–infected leaves of Indian mustard showed significant decrease in oil, triglyceride, 18:2, and 22:1 fatty acid content and also in the level of different lipid classes. Rapeseed–mustard crops are ravaged by Alternaria blight or black spot; the most common widespread and destructive disease is caused mostly by A. brassicae Sacc. infecting all aboveground parts of the plant, reported from all the continents of the world and considered an important constraint in husbandry of oilseed Brassicas. Alternaria longipes and Alternaria napiforme are also reported on rapeseed –mustard from India. A. brassicicola produce some detoxifying enzymes, namely, brassinin hydro-lases, which are dimeric protein of 120 kDa and catalyze the detoxification of brassinin, a phytoalexin produced in crucifers after fungal infection. According to A. K. Tewari, A. brassicae in rapeseed becomes subcuticular after direct penetration. This is followed by colonization of epidermal and the mesophyll cells.