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

Abstract

Wheat stem rust, caused by Puccinia graminis f. sp. tritici Eriks. & E. Henn, can incur yield losses in susceptible cultivars of durum wheat, Triticum turgidum ssp. durum (Desf.) Husnot. Although 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.

Association mapping of resistance to emerging stem rust pathogen races in spring wheat using genotyping‐by‐sequencing

“…Previous mapping work with SNPs and SSR markers located TRTTF resistance on chromosome arm 6AS postulated as Sr8a (Bajgain et al., 2015a; Guerrero‐Chavez, Glover, Rouse, & Gonzalez‐Hernandez, 2015; Hiebert, Rouse, Nirmala, & Fetch, 2016; Nirmala et al., 2017). Similarly, in the current study, a strong association signal was detected on chromosome 6AS suggesting the involvement of Sr8a as it is the only major stem rust resistance gene present in bread wheat effective to TRTTF on chromosome arm 6AS.…”

Genetic Mapping of Loci for Resistance to Stem Rust in a Tetraploid Wheat Collection

“…A number of resistance QTLs identified in the present study are coincident with chromosomal positions of previously reported Sr genes/QTLs based on both linkage and association mapping studies performed on tetraploid and hexaploid wheats. As an example, QTL region 16 on chromosome 6A, was previously identified in biparental populations by [34], and more recently in association mapping panel of durum wheat cultivars by [1,26]. For QTL region 10 on chromosome 4A (Table S1), loci for stem rust resistance were previously identified in both durum and bread wheat, and against several stem rust races, such as TTKSK [26,35,36], TKTTF [37], and TTTTF [38].…”

Identification and Validation of a Common Stem Rust Resistance Locus in Two Bi-parental Populations

“…Five genes, namely Sr2 , Sr55 ( Lr67 / Yr46 / Pm46 ), Sr56 , Sr57 ( Lr34 / Yr18 / Pm38 ), and Sr58 ( Lr46 / Yr29 / Pm39 ), confer adult plant resistance (APR) ( Singh et al, 2015 ), and the 34 genes that impart all stage resistance (ASR) to Pgt race TTKSK are Sr9h , Sr13a , Sr13b , Sr15 , Sr21 , Sr22 , Sr24 , Sr25 , Sr26 , Sr27 , Sr28 , Sr32 , Sr33 , Sr35 , Sr36 , Sr37 , Sr39 , Sr40 , Sr42 , Sr44 , Sr45 , Sr46 , Sr47 , Sr50 , Sr51 , Sr52 , Sr53 , Sr59 , SrCad, SrTA10171 , SrTA10187 , SrTA1662 , SrTmp , and Sr1RS Amigo ( Jin and Singh, 2006 ; Jin et al, 2007 ; Faris et al, 2008 ; Hiebert et al, 2010 ; Kolmer et al, 2011 ; Liu et al, 2011a , b ; Qi et al, 2011 ; Rouse et al, 2011a , 2014 ; Rouse and Jin, 2011 ; Ghazvini et al, 2012 ; Olson et al, 2013a , b ; Bansal et al, 2014 ; Moore et al, 2015 ; Singh et al, 2015 ; Rahmatov et al, 2016 ; Zhang et al, 2017 ). Interestingly, Sr8155B1 does not confer resistance to race TTKSK, but does confer resistance to the more recent variants in the Ug99 race group ( Nirmala et al, 2017 ). Only a few resistance genes ( Sr2 , Sr13a , Sr13b , Sr25 , Sr26 , Sr57 , Sr58 , SrCad , SrTmp , SrND643 , Sr1RS Amigo , and Sr8155B1 ) were found to confer resistance in adapted germplasm ( Jin and Singh, 2006 ; Singh et al, 2008 , 2015 ; Njau et al, 2010 ; Hiebert et al, 2011 ; Basnet et al, 2015 ; Nirmala et al, 2017 ; Zhang et al, 2017 ).…”

“…Interestingly, Sr8155B1 does not confer resistance to race TTKSK, but does confer resistance to the more recent variants in the Ug99 race group ( Nirmala et al, 2017 ). Only a few resistance genes ( Sr2 , Sr13a , Sr13b , Sr25 , Sr26 , Sr57 , Sr58 , SrCad , SrTmp , SrND643 , Sr1RS Amigo , and Sr8155B1 ) were found to confer resistance in adapted germplasm ( Jin and Singh, 2006 ; Singh et al, 2008 , 2015 ; Njau et al, 2010 ; Hiebert et al, 2011 ; Basnet et al, 2015 ; Nirmala et al, 2017 ; Zhang et al, 2017 ). The continuous search for new resistance sources and following through with their genetic characterization and strategic deployment is necessary for long-term control of the fast-evolving races of the stem rust fungus.…”