The stem, black and cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. Crop species which are affected by the disease include bread wheat, durum wheat, barley and triticale. An epidemic of stem rust on wheat caused by race TTKSK (e.g. isolate Ug99) 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. The strain was named after the country where it was identified (Uganda) and the year of its discovery (1999). It spread to Kenya, then Ethiopia, Sudan and Yemen, and is becoming more virulent as it spreads. Scientists are working on breeding strains of wheat that are resistant to UG99. However, wheat is grown in a broad range of