Mycelia that propagates in the secondary host of puccinnia
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The stem, black, and cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale.[1] These diseases have affected cereal farming throughout history. Since the 1950s, wheat strains bred to be resistant to stem rust have become available.[2] Fungicides effective against stem rust are available as well.[3]
In 1999 a new virulent race of stem rust was identified that most current wheat strains show no resistance against. The race was named TTKSK (e.g. isolate Ug99), named after the country where it was identified (Uganda) and the year of its discovery (1999).[4] It spread to Kenya, then Ethiopia, Sudan and Yemen, and is becoming more virulent as it spreads.[4] An epidemic of stem rust on wheat caused by race TTKSK is currently spreading across Africa, Asia and the Middle East and is causing major concern due to the large numbers of people dependent on wheat for sustenance. Scientists are working on breeding strains of wheat that are resistant to UG99. However, wheat is grown in a broad range of environments. This means that breeding programs would have extensive work remaining to get resistance into regionally adapted germplasms even after resistance is identified.[4]
An outbreak of another virulent race of stem rust, TTTTF, took place in Sicily in 2016, suggesting that the disease is returning to Europe.[2]