Discovery of a Novel Stem Rust Resistance Allele in Durum Wheat that Exhibits Differential Reactions to Ug99 Isolates.

Wheat stem rust, caused by f. sp. Eriks. & E. Henn, can incur yield losses in susceptible cultivars of durum wheat, ssp. (Desf.) Husnot. Although several durum cultivars possess the stem rust resistance gene , additional genes in durum wheat effective against emerging virulent races have not been described. Durum line 8155-B1 confers resistance against the f. sp. race TTKST, the variant race of the Ug99 race group with additional virulence to wheat stem rust resistance gene However, 8155-B1 does not confer resistance to the first-described race in the Ug99 race group: TTKSK. We mapped a single gene conferring resistance in 8155-B1 against race TTKST, , to chromosome arm 6AS by utilizing Rusty/8155-B1 and Rusty*2/8155-B1 populations and the 90K Infinium iSelect Custom bead chip supplemented by KASP assays. One marker, , cosegregated with in both populations and correctly predicted presence or absence in 11 durum cultivars tested. We confirmed the presence of in cultivar Mountrail by mapping in the population Choteau/Mountrail. The marker developed in this study could be used to predict the presence of resistance to race TTKST in uncharacterized durum breeding lines, and also to combine with resistance genes effective to Ug99 such as The map location of cannot rule out the possibility that this gene is an allele at the locus. However, race specificity indicates that is different from the known alleles and .