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Title:   Author  item
                                            CHEN, SHISHENG - University Of Californiaitem
                                            Rouse, Matthew

                                                         - *Matt*item
                                            ZHANG, WENJUN - University Of Californiaitem
                                            Jin, Yueitem
                                            AKHUNOV, EDUARD - Kansas State Universityitem
                                            WEI, YUMING - Sichuan Universityitem
                                            DUBCOVSKY, JORGE - University Of California
  Submitted to: Theoretical and Applied Genetics
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/10/2015
                                    Publication  Date: 1/30/2015
                                    Citation: Chen, S., Rouse, M.N., Zhang, W., Jin, Y., Akhunov, E., Wei, Y., Dubcovsky, J. 2015. Fine mapping and characterization of Sr21, a temperature-sensitive diploid wheat resistance gene effective against the Puccinia graminis f.sp. tritici Ug99 race group. Theoretical and Applied Genetics. 128:645–656.Interpretive Summary: Wheat stem rust is a fungal disease of wheat that decreases yield. A strain of the wheat stem rust fungus known as Ug99 emerged in Uganda in 1999 and threatens global wheat production because it is able to infect nearly all wheat varieties. We determined that a wheat gene that confers resistance to Ug99 is effective only at high temperatures. We also identified the location of this gene, named Sr21, within a specific wheat chromosome arm . The molecular markers that we identified as linked to this gene can be used in wheat breeding to select for resistance to Ug99. The identification these molecular markers will facilitate the improvement of resistance of United States wheat cultivars to the dangerous Ug99. Ug99 resistant wheat cultivars will protect United States wheat production from yield loss if a Ug99 epidemic were to occur in the United States.
                                Technical Abstract: A new race of Puccinia graminis f. sp. tritici, the causal pathogen of stem rust of wheat, designated TTKSK (also known as Ug99) and its variants are virulent to most of the stem rust resistance genes currently deployed in 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 susceptible, high infection type reactions have been also reported. 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 the source of
previous inconsistencies. This result indicates that, although Sr21 is a useful tool 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 F2 plants) we mapped Sr21 approximately 50 cM from the centromere on the long arm of chromosome 2Am 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 into common wheat, accelerate Sr21 deployment in wheat breeding programs, and facilitate the map-based cloning of this gene.


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