Progress and prospects in discovery and use of novel sources of stem rust resistance
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.