Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat worldwide. In Ethiopia, grain yield loss in wheat cultivars ranges from 30 to 69%. The use of resistant cultivars is the most economical and environmentally friendly method of controlling the disease. Gene postulation which is based on the gene-for-gene interaction between the host line and the pathogen races is commonly used to determine resistance genes in wheat cultivars. In the present study Yr genes in 22 bread wheat cultivars were studied by testing them, together with the 24 differential lines, with 20 Pst races that were collected from Ethiopia, France and Germany. These cultivars were postulated to have different combinations of stripe rust resistance genes Yr2, Yr3a, Yr4a, Yr6, Yr7, Yr8, Yr9, Yr27, Yr32 and YrSU. Among these genes, Yr2, Yr6, Yr7, Yr8, Yr9, Yr27 and Yr32 could not provide adequate control. This indicates the need for searching more effective resistance genes to be incorporated in Ethiopian bread wheat cultivars. Bread wheat cultivars Wabe and Tusie were resistant to all 20 races, similar to the differential lines with Yr5, Yr15 and Yr26. In addition, due to the absence of matching response spectra to the tested differential genotypes, the Yr gene(s) in bread wheat cultivar Suf-Omer could not be determined. However, the molecular experiments mapped Yr genes in cvs Wabe and Tusie on chromosome 7BL and 3BL in cv. Suf-Omer, showing that the resistance in these cultivars are governed by genes different from Yr5 (2BL), Yr15 (1BL), and Yr26 (1BS).
