Combination of resistance tests and molecular tests to postulate the yellow rust resistance gene Yr17 in bread wheat lines

Yellow rust caused by Puccinia striiformis is a wheat disease of worldwide importance. The Yr17 resistance gene introgressed from Aegilops ventricosa was effective, in France, against all yellow rust isolates until 1998. The SC‐Y15 marker is one of three molecular markers closely linked to Yr17. In this paper, results obtained are compared with the molecular marker SC‐Y15 and with resistance tests performed at the seedling and adult plant stages on 31 lines from five populations derived from recurrent selection programmes. The resistance tests showed that Yr17 controlled the resistance in seven lines, but that others had additional resistance at the adult stage (18 lines). The molecular test corresponded well with the resistance test in most lines (98% of 156 plants tested), including individual plants that were resistant or susceptible in heterogeneous lines. It also indicated the presence of Yr17 in lines in which it could not be identified by the resistance test because of the presence of other genes. Three of the 156 plants tested appeared to have the gene Yr17 according to the resistance tests, but lacked the molecular marker. These could have resulted from breakage of the linkage, the number being consistent with the estimate of linkage already published. This indicated the need for a resistance test, at least in later stages of breeding programmes, if it is considered essential to have the Yr17 gene present. The use of the selected lines in breeding programmes is also discussed.