A number of stem rust resistance genes derived from wild relatives of wheat appeared to be more effective against race TTKSK (Ug99) of Puccinia graminis f. sp. tritici than Sr genes of wheat origin. In an attempt to identify sources of stem rust resistance genes effective against TTKSK, we evaluated several cultivated and wild relatives of wheat for resistance to TTKSK and other stem rust races with broad virulence in seedling tests. Preliminary results indicated that TTKSK resistance could readily be found, but frequencies of resistance varied among the species. Aegilops speltoides had the highest frequency of resistance (nearly 100%). Other species having high frequencies of TTKSK resistance included triticale (77.7% of 567 accessions), Triticum urartu (96.8% of 205 accessions), and T. monococcum (61% of 1020 accessions). Frequencies of TTKSK resistance in other species were: 14.7% in Ae. tauschii (456 accessions), 15% in T. timopheevii (298 accessions), and 17% in T. turgidum ssp. dicoccoides (157 accessions). Based on specific infection types to several races, we postulated that novel genes for resistance to TTKSK are present in some of these species. Accessions with putatively new resistance genes were selected to develop crosses for introgressing resistance into wheat and for developing mapping populations.
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Stem rust, caused by Puccinia graminis f. sp. tritici, is a highly destructive fungal disease of wheat. This pathogen has been effectively controlled in western Canada through resistance since the 1950s. In 1999, a new highly virulent race of stem rust was identified in Uganda. The new strain, named “Ug99”, was given the North American race designation TTKSK. In situ screening has demonstrated that approximately 75% of Canadian wheat cultivars are susceptible to this new race of stem rust. Fortunately, two cultivars, Peace and AC Cadillac, were highly resistant to Ug99. A doubled haploid population was generated from the cross: RL6071/Peace, where RL6071 was the stem rust susceptible parent. In 2008, 189 DH lines from this population were evaluated for response to Ug99 in Kenya. RL6071 and Peace were rated: 80 S and 5 R, respectively. Disease ratings of the DH lines, ranged from 80 S to 1 R. Mendelian evaluation of the stem rust scores indicated a two-gene model (X2=5.51; 0.25<P<0.10; d.f.=3) of inheritance. Peace has the positive allele for the diagnostic Lr34 DNA marker (csLVMS1) published by Spielmeyer et al. (2008). It is believed that Peace carries Lr34 and that this gene may be one of the genes responsible for Ug99 resistance in this cultivar. Molecular mapping of the Ug99 resistance in cultivar Peace is underway.