Stem rust caused by Puccinia graminis f. sp. tritici is one of the most important diseases of wheat in Ethiopia. The pathogen can produce new races that can overcome resistant varieties and cause epidemic under favorable environmental conditions resulting in serious yield losses. The study was carried out to determine the virulence spectrum of Puccinia graminis f. sp. tritici in northwest Ethiopia. Eighty-six stem rust samples were collected during 2017 and 2018 cropping seasons and analyzed on 20 standard stem rust differential lines which resulted in the identification of four races (TTTTF, TKTTF, TKPTF, and TTRTF). Of these races, 60.4 and 60% of the isolates were TTTTF followed by 38.7 and 37.3% of TKTTF (Digalu race) in 2017 and 2018, respectively. These two races accounted for almost 99% of the stem rust population. The least virulent races were TKPTF and TTRTF that accounted 1% in both seasons and were detected only at single location (Farta in South Gondar in 2017 and Amba Giorgis in North Gondar in 2018). The differential hosts carrying resistance genes Sr5, Sr21, Sr9e, Sr7b, Sr6, Sr8a, Sr9g, Sr36, Sr17, Sr9a, Sr9d, Sr10, SrTmp, Sr38 and SrMcN were susceptible to the four races identified in northwest Ethiopia. Two differential hosts carrying the resistant genes Sr24 and Sr31 were effective against all the four races identified in this study. Absence of virulence against lines carrying Sr31 in the present and Sr24 in the present and previous studies suggests that these genes may serve as a source of resistance in combination with other wheat stem rust management systems to the current rust races in northwest Ethiopia.
