Puccinia graminis

Puccinia graminis is a basidiomycete rust fungus that causes stem rust, also known as cereal rust, black rust or red rust, one of the most damaging diseases of wheat and other cereals, producing brick-red pustules on stems and leaves that darken to black as the plant matures. It attacks bread wheat, durum wheat, barley, triticale, and, depending on the formae speciales involved, oats and rye, and completes its life cycle using barberry as an alternate host alongside its cereal hosts. Concern over stem rust dates back at least to Aristotle, and the disease destroyed more than a fifth of United States wheat crops in several years between 1917 and 1935; the emergence of the highly virulent Ug99 race in 1999 renewed global alarm and prompted a 40 million dollar grant from the Bill and Melinda Gates Foundation for resistance research in 2011.