Stem rust (Puccinia graminis) and powdery mildew ( Blumeria graminis) are persistent threats to hexaploid wheat ( Triticum aestivum L., 2n=6x=42, AABBDD) production worldwide. Genetic variation for disease resistance has been limited in the D genome of wheat due to restricted gene flow between T. aestivum and the diploid D genome progenitor species, Aegilops tauschii Coss. (2 n=2x=14, DD). One method to introgress disease resistance from Ae. tauschii to wheat is through direct hybridization and backcrossing with wheat. Using this method, the Ug99-effective stem rust resistance gene SrTA10187 was previously introgressed from Ae. tauschii accession TA10187 and mapped to wheat chromosome 6DS. Development of a high-resolution genetic map surrounding SrTA10187 assigned the resistance locus to a 1.1 cM interval on 6DS and enabled candidate gene identification. To introgress and map powdery mildew resistance in the D genome, introgression lines (ILs) were developed by direct hybridization of the resistant Ae. tauschii accession TA1662 with the susceptible wheat line KS05HW14. Following embryo rescue and recurrent backcrossing to KS05HW14, ILs were developed that only segregate for D genome alleles. Using a combination of genotyping-by-sequencing and KASP2122 SNP markers, a novel powdery mildew resistance gene, designated Pm58, was mapped to 2DS and confirmed to be effective under field conditions. Powdery mildew resistant germplasm, fixed for Pm58 were released for immediate use in disease resistance breeding. -- Abstract.
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