Black rust of wheat is caused by Puccinia graminis tritid. The later is a heteroecious parasite possess dikaryophase and haplophase. Penicillium grows as saprophyte on decaying fruits and vegetables. They cause considerable damage to leather goods, fabrics and furniture. They cause rot and decay of lemon, orange. Rhizopus growing frequently on bread and thus called, bread mold. It lives as a saprophyte. Yeasts have the ability to ferment carbohydrate. In absence of O2 the organic acid is split into CO2 and alcohol. These products are of immense value to the baking and brewing industries.