Stem rusts on wheat, barley, and oat in Canada in 1999

Stems of wheat, barley, and oat infected with stem rust were collected throughout Canada in 1999 to determine the virulence spectrum of Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn. and Puccinia graminis f. sp. avenae Eriks. & E. Henn. To distinguish seven different pathotypes, 99 isolates of P. graminis tritici obtained from wheat were inoculated onto differential sets of wheat lines with single genes for stem rust resistance. The predominant pathotypes were RCRSK (60.3%), QCCJN (15.4%), and QFCSR (11.5%). The spring wheat cultivars currently grown in Canada are resistant to these pathotypes. Among 178 isolates of P. graminis tritici recovered from barley, eight pathotypes were identified, with QCCJN (53.4%), RCRSK (18.5%), and QCCJL (14.0%) predominating. Pathotypes QCCJL and QCCJN represented 67.4% of the isolates from barley. Since these pathotypes are highly virulent on the barley cultivars currently grown in Canada, there continues to be a threat to barley production due to stem rust. Ten pathotypes were identified among 269 R graminis avenae isolates from wild and cultivated oat. The predominant pathotypes, NA29 at 45.3% and NA67 at 26.4% from wild oat, and NA67 at 31.8% and NA29 at 30.9% from cultivated oat, were relatively similar in occurrence. Pathotype NA67, discovered for the first time in western Canada in 1998, is virulent on Pg2, Pg9, and Pg13, which, in various combinations, conditioned resistance to stem rust in most oat cultivars prior to 1998. The incidence of pathotype NA67 in cultivated oat front Manitoba and Saskatchewan increased from 21.7% in 1998 to 34.7% in 1999. A new pathotype, NA76, was identified, which was also virulent on the combination of Pg2, Pg9, and Pg13 but, unlike NA67, was avirulent to Pg15.