Black stem rust is caused by Puccinia graminis tritici. The genus Puccinia includes 700 species, which cause rust diseases of many economic plants such as wheat, barley, oats, etc. It is called a rust because of the reddish brown colour of the spores that are found chiefly upon the surface of the host leaves and stems. P. graminis is heteroecious, i.e., requiring two hosts, wheat and barberry for the completion of normal life cycle.

According to the nature of the spores, the life cycle of the P. graminis is divided into five stages. It is during, teleuto stage, the teliospore (or teleutospores) produce dark brown to black pustules on the surface of stems and leaves of the wheat that results into ‘black stem rust of wheat’.