STEM RUSTS ON WHEAT, BARLEY, AND OAT IN CANADA IN 1993

In 1993, stem rusts of wheat and barley (Puccinia grantinis f. sp. tri tici) and of pat (P. graniinis f. sp. avenae) were first observed in M anitoba August 3. Lower than normal temperatures in the prairie region limited stem rust development. Maximum infections of 5% and 1% respec tively developed in lines of susceptible wheat in nurseries and in com mercial barley fields in the prairie region. These infection levels we re too low to cause significant damage. Infections of wild oat were co nfined to Manitoba, and remained light. An additional subset of differ ential genes (Sr9a, Sr9d, Sr10, SrTmp) for P. graminis f. sp tritici w as added in 1993, thus identifying races with a four-letter code. Alth ough race QCCJ decreased in prevalence in the prairie region in 1993, it was the most common race (42.7%) collected from all sources in Cana da, followed by race TPMK (40.2%). Race QCCJ was the most common (68.8 %)in collections from cultivated barley, and race TPMK was most freque ntly isolated (58.6%) from wheat. Other races from wheat were QFCS (18 .9%), QCCJ (16.7%), RCRS (3.6%), QFCJ (1.4%), RKQQ (0.5%), and RKRQ (0 .5%); from cultivated barley, races were TPMK (23.4%), QFCS (7.1%), an d TMRT (0.7%); and from wild barley, races QCCJ (42.7%), TPMK (38.7%), QFCS (13.3%), QCRS (1.3%), RCCJ (1.3%), RHRS (1.3%), and RKQQ (1.3%). All isolates of P. graminis f. sp. tritici from wheat from western Ca nada were virulent to genes Sr5, Sr21, Sr9g, Sr9d, and Sr17, and, in a ddition, to Sr10 from cultivated barley. All isolates were avirulent t o genes Sr13, Sr22, Sr24, Sr25, Sr26, Sr27, Sr29, Sr30, Sr32, and Sr37 . From eastern Canada, races NA26 and NA32 of P. graminis f. sp. avena e, virulent to gene Pg13, continued to increase in prevalence in 1993. From western Canada, races NA27 and NA29 were the most common, but th ese races are avirulent to the resistance genes now used in western Ca nadian oat cultivars.