Epidemics of Stripe Rust On Wheat and Barley and Races of Puccinia Striiformis Identified in the Western United States in 2010 and 2011.

Due to the ideal weather conditions in 2010 and 2011, severe epidemics of wheat stripe rust caused huge yield losses and widely use of fungicides in the western US, particularly in Californian, Idaho, Montana, Oregon, Utah, and Washington. A total of 529 viable wheat stripe rust samples collected from the six states and 48 viable barley stripe rust samples collected from CA, ID, OR, UT, and WA were tested for identifying PSTv and PSH races, respectively. From the wheat stripe rust samples, 46 PSTv races were detected in the region; and 33, 17, 14, 10, 9, and 6 race were identified from WA, CA, ID, MT, OR and UT, respectively. Five predominant races are PSTv-11 (virulent to Yr1, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44, YrExp2, and YrTye) (35.0%), PSTv-14 (similar to PSTv-11 plus virulent to YrTr1) (12.5%), PSTv-37 (similar to PSTv-14 except avirulent on Yr1 and YrTye) (12.35%), PSTv-4 (virulent to Yr1, Yr6, Yr9, Yr17, Yr27, YrSP and YrTye) (4.2%), and PSTv-41 (virulent to Yr6, Yr7, Yr8, Yr9, Yr10, Yr17, Yr24, Yr27, Yr32, Yr43, Yr44, YrTr1, and YrExp2) (3.4%). PSTv-11 and PSTv-37 distributed throughout the region; PSTv-14 was mainly in MT and WA; and PSTv-4 and PSTv-41 were mostly detected from WA. Among the 46 races, the numbers of virulences on the 18 single Yr-gene differentials ranged from 0 (PSTv-18) to 16 (PSTv-51). High virulence frequencies (>80%) were detected for Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr44, and YrExp2; moderate (40-80%) for Yr1, Yr43, YrTr1 and YrTye; low (<10%) for Yr10, Yr24, Yr32, and YrSP; and none for Yr5 and Yr15. A total of 12 previously named PSH races were identified from the 48 barley samples collected form CA, ID, MT, OR, UT, and WA. PSH-33 (virulent on Topper and Abed Binder 12) was predominant (52%) followed by PSH-46 (virulent on Topper, Abed Binder 12, and Trumpf) (13%) and PSH-54 (virulent on Topper, Abed Binder 12, Trumpf, and Bancroft) (13%). The race information is useful for control of stripe rust using resistance.