noun
1. : a rust attacking the stem of a plant ; especially : a destructive disease of wheat and various other grasses that is caused by a rust fungus ( Puccinia graminis ), is characterized by reddish brown lesions in the uredostage of the parasite and black lesions in the teliospore stage, and involves plants of the genera Berberis or Mahonia as alternate hosts of the parasite
2. : the fungus causing stem rust