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 world ide 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 SC-Y15. I n this paper, results obtained are compared with the molecular marker SC-Y1 5 and with resistance tests performed at the seedling and adult plant stage s on 31 lines from five populations derived from recurrent selection progra mmes. The resistance tests showed that Yr17 controlled the resistance in se ven lines, but that others had additional resistance at the adult stage (18 lines). The molecular test corresponded well with the resistance test in m ost lines (98% of 156 plants tested). including individual plants that were resistant or susceptible in heterogeneous lines. It also indicated the pre sence of Yr17 in lines in which it could not be identified by the resistanc e test because of the presence of other genes. Three of the 156 plants rest ed appeared to have the gene Yr17 according to the resistance tests, but la cked the molecular marker. These could have resulted from breakage of the l inkage. the number being consistent with the estimate of linkage already pu blished. This indicated the need for a resistance test, at least in later s tages of breeding programmes, if it is considered essential to have the Yr1 7 gene present. The use of the selected lines in breeding programmes is als o discussed.