Resistance to race TTKSK of Puccinia graminis f. sp. tritici in tetraploid wheat

A group of races of Puccinia graminis f. sp. tritici in the TTKS (or Ug99) lineage possess broad virulence to wheat cultivars worldwide, and only a few genes in the adapted cultivars have resistance to these races. In attempts to identify new stem rust resistance genes effective against race TTKSK, we evaluated cultivated tetraploid wheat (T. turgidum ssp. dicoccum, ssp. carthlicum, ssp. polonicum, ssp. turanicum, and ssp. turgidum) for resistance to TTKSK and other races with broad virulence. A high frequency of TTKSK resistance at the seedling stage was observed, as 207 (21% of 1002 accessions) exhibited low infection types. Low infection types ranging from 2= to 2+ to race TTKSK were predominant. Studies to determine the genetic basis of TTKSK resistance at the seedling stage revealed that resistance in tetraploid wheat is conferred mostly by single genes. Fifty accessions were evaluated for resistance to TTKSK and Ethiopian races in the field screening nursery at the Ethiopian Institute for Agricultural Research (Debre Zeit, Ethiopia). Twenty-three accessions exhibited resistant to moderately resistant responses to stem rust. Four accessions susceptible to TTKSK at the seeding stage were resistant at the adult stage. These accessions may possess adult plant resistance. Since all these tetraploid species share the same genome as durum wheat and are in cultivated form, resistance genes could be easily transferred to durum wheat by conventional breeding approaches.