Determining the Order of Resistance Genes to Stagonospora nodorum Blotch, Fusarium Head Blight and Stem Rust and Combining them in Coupling on Wheat Chromosome 3BS

A variety of diseases of wheat (Triticum aestivum L.) occurs every year in the U.S. leading to significant grain yield losses.  Stagonospora nodorum blotch (SNB), fusarium head blight (FHB) and stem rust (SR) are caused by the fungi Stagonospora nodorum, Fusarium graminearum and Puccinia graminis, respectively.  These diseases penalize not only the grain yield but also its quality.  Three resistance factors, Qsng.sfr-3BS, Fhb1 and Sr2 conferring resistance, respectively, to SNB, FHB and SR, each from a unique donor wheat parent line, have been mapped to chromosome arm 3BS of the wheat genome and are believed to be closely linked.  Based on previously published analyses, Sr2 is on the distal end, Fhb1 is on the proximal end and Qsng.sfr-3BS is in the middle of Sr2 and Fhb1 in the 3BS region of the wheat genome.  Thus, the objectives of this project are to determine the gene order of Qsng.sfr-3BS, Fhb1 and Sr2, in a linkage block on chromosome 3BS and combine them in coupling.  A total of 1,600 F₂ plants was screened, along with the parental lines, using KASPar genotyping technology to identify the recombinant progeny.  Single-nucleotide polymorphism markers were utilized to identify the recombinants, determine the gene order and to make the genetic map.  Phenotypic screening for SNB was performed on the entire F₂ population.  Knowing the positional order of these resistance genes will enable the development of a wheat line with all three genes in coupling to provide durable and broad-spectrum resistance against three major leaf and head diseases.