Discovery of a novel stem rust resistance allele in durum wheat that exhibits differential reactions to Ug99 isolates

Authors: NIRMALA, JAYAVEERAMUTHU - University Of Minnesota; SAINI, JYOTI - North Dakota State University; NEWCOMB, MARIA - University Of Minnesota; OLIVERA, PABLO - University Of Minnesota; Gale, Sam; Klindworth, Daryl; ELIAS, ELIAS - North Dakota State University; TALBERT, LUTHER - Montana State University; Chao, Shiaoman; Faris, Justin; Xu, Steven; Jin, Yue; Rouse, Matthew - Matt

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2017
Publication Date: 8/28/2017
Citation: Nirmala, J., Saini, J., Newcomb, M., Olivera, P., Gale, S.W., Klindworth, D.L., Elias, E., Talbert, L., Chao, S., Faris, J.D., Xu, S.S., Jin, Y., Rouse, M.N. 2017. Discovery of a novel stem rust resistance allele in durum wheat that exhibits differential reactions to Ug99 isolates. G3, Genes/Genomes/Genetics. 7:3481-3490.

Interpretive Summary: The disease wheat stem rust threatens United States wheat production because a new strain of the wheat stem rust pathogen called Ug99 is virulent to the majority of wheat varieties worldwide and few genetic resources are available that confer resistance, especially in durum wheat. We discovered a unique stem rust resistance gene called Sr8155B1 present in durum wheat that is effective to most isolates of the Ug99 race group. We identified molecular markers linked to Sr8155B1 that can be used to select for Ug99-resistance in durum wheat breeding. We evaluated the effectiveness predicting Ug99-resistance with Sr8155B1-linked markers in both a panel of durum varieties and a durum/common wheat interspecific population. We recommend the selection and release of durum wheat varieties that possess both Sr8155B1 and previously characterized Ug99-effective Sr13 for maximum immediate protection of United States durum wheat from the threat of Ug99.

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