Distribution of Wheat Stem Rust (Puccinia Graminis F. Sp. Tritici) in Westand Southwest Shewa Zones and Identification of its Phsiological Races

Stem rust (black rust) caused by Puccinia graminis f.sp.tritici is one of the most important air borne diseases of wheat (Triticum aestivum) in the central high lands of Ethiopia, including west and southwest Shewa zones. The pathogen is capable to produce new physiological races that attack resistant varieties and develop epidemic under favorable environmental conditions which results in a serious yield loss. However, information on the status of stem rust distribution and races in west and southwest Shewa zones is lacking. Therefore, the present studies were based on stem rust survey to compute the prevalence and intensity of disease; race analysis via inoculation of stem rust isolates and multiplication of single-pustule of the pathogen and race designation by inoculating on wheat differential lines. Eighty six wheat fields were assessed in 12 districts of west and south west Shewa zones with altitude ranges between1925-2915 m.a.s.l. Seventy five (87.2%) wheat fields infected with stem rust had the overall mean of 33% incidence and 10.8% severity. The mean prevalence of stem rust was 96.3% in southwest and 83.1% in west Shewa zones, whereas, the mean incidence was 34.7% and 31.2% in west and southwest Shewa zones, respectively. Similarly, mean severity was 14.5% in west and 7.1% in southwest Shewa zones. Forty five stem rust samples collected during the survey were analyzed on the twenty standard stem rust differentials and resulted in identification of 5 races (TTTTH, TTKSK, TKTTF, HKPPF & HKNTF). Of these, 88.4% of the isolates were TKTTF (Digalu race) followed by 4.7% of the isolates by TTKSK (Ug99). Among the five races, the most virulent, which made 18 Sr genes non-effective was TTTTH. TKTTF and TTKSK races were virulent on 85% of Sr genes. Differential host carrying Sr24 was an effective gene which confers resistance to all of the races identified in the area. On the other hand, the wheat differential hosts carrying the resistance genes Sr McN, Sr10, Sr9a, Sr30, Sr9g, Sr8a, Sr6, Sr7b and Sr21 were ineffective to 100% of the isolates tested. Hence, the Sr resistance gene Sr24 can be used as sources of resistance in wheat breeding program.