Evaluation of Aegilops tauschii Coss. for resistance to wheat stem rust and inheritance of resistance genes in hexaploid wheat

With the objective to identify new sources of resistance to wheat stem rust, a collection of 169 accessions of Aegilops tauschii, obtained from the IPK genebank at Gatersleben, Germany, were screened for resistance under controlled conditions. Fourteen (8%) accessions were resistant to stem rust among which 10 were highly resistant ( IT 5; and 1) and four exhibited a moderately resistance reaction ( IT 5 2). From the synthetic hexaploids which were produced by hybridizing resistant Ae. tauschii with susceptible Triticum durum, six synthetics expressed a high level of stem rust resistance similar to their corresponding diploid parents, while five displayed either a reduced or complete susceptibility compared to their Ae. tauschii parents. This suppression of resistance at the hexaploid level suggests the presence of suppressor genes in the A and/or B genomes of the T. durum parents. Inheritance of resistance from crosses of five stem rust resistant synthetic hexaploids with two susceptible T. aestivum genotypes revealed that three of the synthetics (syn 101, syn 601 and syn 801) possessed one dominant gene each, syn 111 has two different dominant genes and syn 116 has two complementary interacting genes for stem rust resistance. Intercrosses among the four stem rust resistant synthetic hexaploids indicated that the putative genes conferring stem rust resistance in each of the synthetics are neither allelic nor closely linked to each other.