Wheat stem rust severity was determined using stratified simple random sampling
technique and physiological races of Puccinia graminis f.sp. tritici
were determined using the 20 North American wheat stem rust differentials.
Results revealed a significant variation in wheat stem rust severity in the
region. Lower wheat stem rust severity of 12.5% was observed in high altitude
areas of Kipkabus having more than 2200 m above sea level. High wheat stem rust
severity of 34 and 32% was observed in Mois Bridge and Moiben, respectively.
These areas had lower altitude of less than 1900 mean sea level. Four wheat
stem rust races were reported in this region. The predominant race was TTKST
(Ug99+Sr24) at 66.7% predominance, followed by race TTKSK (Ug99)
at 21.1%, race PTKST (Sr31+Sr24-Sr21) at 10.5% and race TTTSK (Ug99+Sr36)
at 1.8%. A new race PTKST was reported at Chepkoilel, Moiben and Mois Bridge.
There was no significant correlation (r = 0.398) of stem rust severity and race
diversity. However, there was a significant negative correlation (r = -0.461)
of race diversity and altitude and a highly significant negative correlation
(r = -0.713) of altitude and stem rust severity. The study concluded that wheat
stem rust severity varied depending on altitude and location, and four races
are present in North Rift region of Kenya, where the predominant race is TTKST
(Ug99+Sr24).