小麦白粉病是一种世界性真菌病害，是严重影响我国小麦高产稳产的三大病害之一，发掘利用新抗源是培育抗病品种、经济有效地防治小麦白粉病危害的迫切需求。本申请人利用河南省白粉菌混合流行菌株接种，首次在西尔斯山羊草2Ss染色体上发现了抗白粉病新基因，暂定名为Pm2Ss。在此基础上，本项目拟用2Ss[2B]代换系和诱导部分同源染色体重组的ph1b突变体为亲本，构建ph1bph1b背景的2Ss/2B大规模分离群体，创制一系列不同2Ss片段长度和重组位点的2Ss-2B重组体；并利用KASP标记、白粉病接种鉴定和基因组原位杂交多种技术对Pm2S基因进行精细定位；然后利用差异表达基因谱、抗病基因同源序列克隆和同科异种基因共线性分析发掘其候选抗病基因。项目可以为小麦抗病育种提供新抗源和共分离分子标记，并为该基因的分离和进一步了解小麦抗白粉病的分子机理奠定基础。

Powdery mildew of wheat, caused by Blumeria graminis f.sp. tritici (Bgt), is devastating disease worldwide and one of the three most sever diseases damaging wheat yields and production stability in China . Discovery and application of novel genes of powdery mildew resistance is always in urgent need to develop resistance varieties of wheat，and thus to prevent wheat crops from the disease economically and effectively . A novel resistant gene derived from Aegilops searsii has been identified by the applicants as the result of powdery mildew resistance assays using Bgt races popular in Henan Province. The gene was located at chromosome 2Ss of Ae. searsii and temporarily designated as Pm2Ss. On the basis of this, here propose a project to develop a series of 2Ss-2B recombinant, construct fine map and discover resistant gene candidates for the further cloning of the gene and understanding molecular mechanism of the resistance to powdery mildew. To accomplish the objectives, a specific 2Ss/2B double monosomic segregating population with homoelogous recombination inducing gene (ph1b) backgrounds will be developed to increase the recombinant efficiency of 2Ss/2B and develop a series of 2Ss-2B recombinant. Single nucleotide polymorphism genotyping using Kompetitive Allele Specific PCR (KASP), powdery mildew assays by inoculation and improved genomic in situ hybridization will further be applied to the 2Ss-2B recombinant series and the segregation population for Pm2Ss fine mapping, and differential expressed gene analysis, resistant gene homology - based cloning, and colinearity or synteny analysis will also be used to discover candidates of the novel gene Pm2Ss. The accomplish of the project will provide a novel gene and co-segregated molecular markers of the gene for wheat resistance breeding, and lay the foundations for the further understanding of the molecular mechanism of the resistance to wheat powdery mildew.