A robust molecular marker for the detection of shortened introgressed segment carrying the stem rust resistance gene Sr22 in common wheat

Stem rust resistance gene Sr22 transferred to common wheat from Triticum boeoticum and T. monococcum remains effective against commercially prevalent pathotypes of Puccinia graminis f. sp. tritici, including Ug99 and its derivatives. Sr22 was previously located on the long arm of chromosome 7A. Several backcross derivatives (hexaploid) possessing variable sized Sr22-carrying segments were used in this study to identify a closely linked DNA marker. Expressed sequenced tags belonging to the deletion bin 7AL-0.74-0.86, corresponding to the genomic location of Sr22 were screened for polymorphism. In addition, RFLP markers that mapped to this region were targeted. Initial screening was performed on the resistant and susceptible DNA bulks obtained from backcross derivatives carrying Sr22 in three genetic backgrounds with short T. boeoticum segments. A cloned wheat genomic fragment, csIH81, that detected RFLPs between the resistant and susceptible bulks, was converted into a sequence tagged site (STS) marker, named cssu22. Validation was performed on Sr22 carrying backcross-derivatives in fourteen genetic backgrounds and other genotypes used for marker development. Marker cssu22 distinguished all backcross-derivatives from their respective recurrent parents and co-segregated with Sr22 in a Schomburgk (+Sr22)/Yarralinka (-Sr22)-derived recombinant inbred line (RIL) population. Sr22 was also validated in a second population, Sr22TB/Lakin-derived F-4 selected families, containing shortened introgressed segments that showed recombination with previously reported flanking microsatellite markers.