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

Abstract

Wheat stem rust, caused by <i>Puccinia graminis</i> f. sp. <i>tritici</i> Eriks. & E. Henn, can incur yield losses in susceptible cultivars of durum wheat, <i>Triticum turgidum</i> ssp. <i>durum</i> (Desf.) Husnot. Although several durum cultivars possess the stem rust resistance gene <i>Sr13</i>, additional genes in durum wheat effective against emerging virulent races have not been described. Durum line 8155-B1 confers resistance against the <i>P. graminis</i> f. sp. <i>tritici</i> race TTKST, the variant race of the Ug99 race group with additional virulence to wheat stem rust resistance gene <i>Sr24</i> 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, <i>Sr8155B1</i>, 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, <i>KASP_6AS_IWB10558</i>, cosegregated with <i>Sr8155B1</i> in both populations and correctly predicted <i>Sr8155B1</i> presence or absence in 11 durum cultivars tested. We confirmed the presence of <i>Sr8155B1</i> 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 <i>Sr8155B1</i> with resistance genes effective to Ug99 such as <i>Sr13</i> The map location of <i>Sr8155B1</i> cannot rule out the possibility that this gene is an allele at the <i>Sr8</i> locus. However, race specificity indicates that <i>Sr8155B1</i> is different from the known alleles <i>Sr8a</i> and <i>Sr8b</i>.