Genetics and mapping of seedling resistance to Ug99 stem rust in Canadian wheat cultivars ‘Peace’ and ‘AC Cadillac’

Abstract

Stem rust (caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) has re-emerged as a threat to wheat production with the evolution of new pathogen races, namely TTKSK (Ug99) and its variants, in Africa. Deployment of resistant wheat cultivars has provided long-term control of stem rust. Identification of new resistance genes will contribute to future cultivars with broad resistance to stem rust. The related Canadian cultivars Peace and AC Cadillac show resistance to Ug99 at the seedling stage and in the field. The purpose of this study was to elucidate the inheritance and genetically map resistance to Ug99 in these two cultivars. Two populations were produced, an F(2:3) population from LMPG/AC Cadillac and a doubled haploid (DH) population from RL6071/Peace. Both populations showed segregation at the seedling stage for a single stem rust resistance (Sr) gene, temporarily named SrCad. SrCad was mapped to chromosome 6DS in both populations with microsatellite markers and a marker (FSD_RSA) that is tightly linked to the common bunt resistance gene Bt10. FSD_RSA was the closest marker to SrCad (≈ 1.6 cM). Evaluation of the RL6071/Peace DH population and a second DH population, AC Karma/87E03-S2B1, in Kenya showed that the combination of SrCad and leaf rust resistance gene Lr34 provided a high level of resistance to Ug99-type races in the field, whereas in the absence of Lr34 SrCad conferred moderate resistance. A survey confirmed that SrCad is the basis for all of the seedling resistance to Ug99 in Canadian wheat cultivars. While further study is needed to determine the relationship between SrCad and other Sr genes on chromosome 6DS, SrCad represents a valuable genetic resource for producing stem rust resistant wheat cultivars.

Allelic variation for the rust resistance gene Lr34/Yr18 in Canadian wheat cultivars

“…Therefore, increased incorporation of Lr34/Yr18 into future cultivars could be useful in protecting the Canadian wheat crop against stripe rust. Stem rust resistance is also conditioned by the Lr34/Yr18 locus (Dyck et al 1985, Hiebert et al 2010. The central role of Lr34/Yr18 in multiple disease resistance makes knowledge of this gene an important consideration in any set of wheat germplasm.…”

“…This resistance has not been overcome by P. triticina in a race-specific manner, over many years of widespread use throughout the world. This locus also enhances resistance conditioned by other leaf rust (German and Kolmer 1992) and stem rust (Hiebert et al 2010) resistance genes. The Lr34/Yr18 locus was cloned ), and molecular markers were developed that are either closely linked to Lr34, or within the coding region of the gene (Dakouri et al 2010;Lagudah et al 2009).…”

“…resistance gene. This locus also confers resistance to stripe rust (Yr18, Singh 1992b), stem rust (Dyck et al 1985;Hiebert et al 2010), powdery mildew (Pm38, Spielmeyer et al 2005), and barley yellow dwarf virus (Bdv1, Singh 1993). Lr34 conditions adult plant, slow rusting resistance and is completely linked with leaf tip necrosis (Singh 1992a).…”

Discovery and molecular mapping of a new gene conferring resistance to stem rust, Sr53, derived from Aegilops geniculata and characterization of spontaneous translocation stocks with reduced alien chromatin

“…Gene pyramiding is facilitated by the ability to use molecular markers closely or completely linked to resistance genes. Molecular markers have been developed for numerous stem rust resistance genes, including: Sr2 (Spielmeyer et al 2003;Hayden et al 2004;Mago et al 2011), Sr6 (Tsilo et al 2009), Sr9a (Tsilo et al 2007), Sr13 (Admassu et al 2011;Simons et al 2011), Sr22 (Khan et al 2005;Olson et al 2010;Periyannan et al 2011), Sr24 (Mago et al 2005), Sr25 (Liu et al 2010), Sr26 (Mago et al 2005;Liu et al 2010), Sr30 (Hiebert et al 2010a), Sr31 (Das et al 2006;Weng et al 2007), Sr32 (Bariana et al 2001), Sr33 (Sambasivam et al 2008), Sr35 (Zhang et al 2010), Sr36 (Bariana et al 2001;Tsilo et al 2008), Sr39 (Gold et al 1999;Mago et al 2009;Niu et al 2011), Sr40 (Wu et al 2009), Sr45 (Sambasivam et al 2008), Sr50 (synonym SrR, Anugrahwati et al 2008), Sr51 (Liu et al 2011), Sr52 (Qi et al 2011), SrCad (Hiebert et al 2010b), and SrWeb (Hiebert et al 2010a). Recent progress on molecular marker development and improved donor sources should accelerate the pyramiding and deployment of cultivars with more durable resistance to stem rust.…”

Races ofPuccinia graminison barley, oat and wheat in Canada in 2006

“…Genes Sr6, Sr7a, Sr7b and Sr9b are the most likely to condition effective resistance in Canadian spring wheat against the stem rust races in the North American population, including race QFCSC. However, the cultivars 'AC Cadillac' and 'Peace' were recently identified to have a non-catalogued resistance gene temporarily designated as SrCad Hiebert et al, 2010) that is effective to all North American races and also to race TTKSK (Ug99). Bulked samples of collections from Saskatchewan and Manitoba were inoculated onto lines considered broadly resistant in order to detect new virulent races.…”