Fine mapping and characterization of Sr21, a temperature-sensitive diploid wheat resistance gene effective against the Puccinia graminis f. sp. tritici Ug99 race group

Abstract

A race of Puccinia graminis f. sp. tritici, the causal pathogen of stem rust of wheat, known as Ug99, and its variants, are virulent to plants carrying stem rust resistance genes currently deployed in most wheat cultivars worldwide. Therefore, identification, mapping and deployment of effective resistance genes are critical to reduce this threat. Resistance gene Sr21 identified in diploid wheat T. monococcum can be effective against races from the Ug99 race group, but both susceptible and partial resistant reactions have been reported in previous studies. To clarify this conflicting information we screened four monogenic lines with Sr21 and four susceptible controls with 16 Pgt isolates including 5 isolates of the Ug99 race group under three different temperatures and three different photoperiods. We observed that temperature influences the interaction between monogenic lines with Sr21 and Ug99 race group isolates, and may be one source of previous inconsistencies. This result indicates that, although Sr21 confers partial resistance against Ug99, its effectiveness can be modulated by environmental conditions and should not be deployed alone. Using two large diploid wheat-mapping populations (total 3,788 F 2 plants) we mapped Sr21 approximately 50 cM from the centromere on the long arm of chromosome 2A m within a 0.20 cM interval flanked by sequence-based markers FD527726 and EX594406. The closely linked markers identified in this study will be useful to reduce the T. monococcum segments introgressed * Corresponding author: J. Dubcovsky, jdubcovsky@ucdavis.edu.

Wheat gene Sr60 encodes a protein with two putative kinase domains that confers resistance to stem rust

“…Finally, the direct incorporation of Sr60 into transgenic wheat plants would avoid this limitation, and has the additional advantage that multiple resistance genes can be incorporated in the same transgenic cassette. The resistance profile of Sr60 could complement well the resistance profiles of genes Sr35 (Zhang et al, 2010), Sr21 (Chen et al, 2015) and SrTm5 (Chen et al, 2018a), which are susceptible to race QFCSC but confer resistance to Ug99. The incorporation of Sr60 to these resistance cassettes can improve resistance to races QFCSC, QTHJC and SCCSC, which were identified in the United States (Dunckel et al, 2015).…”

Multi‐Locus Mixed Model Analysis Of Stem Rust Resistance In Winter Wheat

“…Despite their strong linkage, both markers remained highly significant after being added to the same multiple regression model. Three resistance genes on 2AL ( Sr21 , Sr48 , and SrTm4 ) are known to confer resistance to Pgt race TTKSK (Bansal et al, 2009; Briggs et al, 2015; Chen et al, 2015). Both Sr21 and SrTm4 were originally discovered in the diploid relative Triticum monococcum L. and are not expected to be widespread in hexaploid wheat (McIntosh et al, 1995), thus are unlikely to be linked to IWA1202 and IWA574 in this panel.…”

Characterization of Puccinia graminis f. sp. tritici isolates derived from an unusual wheat stem rust outbreak in Germany in 2013

“…However, one isolate differs in the virulence observed on Sr21 (race TKPTF exhibits a high IT on Sr21). Resistance conferred by Sr21 has been shown to be variable, influenced by temperature, environmental conditions and genetic backgrounds (Chen et al, 2015). Even though these isolates were evaluated three times before the final race assignment was made, this race designation has to be considered as tentative.…”