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ABSTRACT Powdery mildew, caused by the biotrophic fungus Blumeria graminis DC. f. sp. avenae, is a widespread disease of oats, especially in the temperate regions of Western and Central Europe, and the use of resistant varieties is the most sustainable way to ensure stable yields. Therefore, the identification of robust and effective resistance to powdery mildew is of great interest for oat breedinpg. In contrast to race‐specific resistance genes, adult plant resistance (APR) is generally considered to be more durable. The oat variety ‘Firth’, as well as related varieties such as ‘Husky’ or ‘Flämingstip’, contains an unknown APR gene, which was previously located on chromosome 1D using DArT markers. The aim of this study was to confirm and refine the chromosomal location of this resistance gene, tentatively named Pm13. To this end, two independent experiments were carried out using different genetic material under natural infection conditions in the field: genome‐wide association mapping (GWAS) in a diverse set of 250 oat lines grown in 10 environments and QTL mapping in a HuskyxAVE1284 biparental population grown in three environments. Both approaches identified a QTL for powdery mildew resistance on the distal end of chromosome 1D in the hexaploid Sang oat genome. The locus explained up to 15% of the phenotypic variance in GWAS and 64% of the phenotypic variance in QTL mapping. Comparison of field data with results from laboratory leaf segment tests confirmed that Pm13 does indeed confer APR. The sequence information of the identified linked markers may allow the development of molecular markers useful for early selection of oat lines with high levels of APR. [ABSTRACT FROM AUTHOR]

The Pc54 oat line carries the crown rust resistance gene Pc54 and an unknown gene effective against powdery mildew. In this study, two recombinant inbred line (RIL) populations were developed to identify the genomic locations of the two genes and produce lists of molecular markers with a potential for marker-assisted selection. The RILs and parents were phenotyped for crown rust and powdery mildew in a controlled environment. They were also genotyped using the 6K Illumina Infinium iSelect oat single nucleotide polymorphism (SNP) chip. Multiple interval mapping placed Pc54 on the linkage group Mrg02 (chromosome 7D) and the novel powdery mildew quantitative trait locus (QTL) QPm.18 on Mrg18 (chromosome 1A) both in mapping and in the validating populations. A total of 9 and 31 significant molecular markers were identified linked with the Pc54 gene and QPm.18, respectively. Reactions to crown rust inoculations have justified separate identities of Pc54 from other genes and QTLs that have previously been reported on Mrg02 except for qPCRFd. Pm3 is the only powdery mildew resistance gene previously mapped on Mrg18. However, the pm3 differential line, Mostyn, was susceptible to the powdery mildew race used in this study, suggesting that Pm3 and QPm.18 are different genes. Determining the chromosomal locations of Pc54 and QPm.18 is helpful for better understanding of the molecular mechanism of resistance to crown rust and powdery mildew in oats. Furthermore, SNPs and single sequence repeats that are closely linked with the genes could be valuable for developing PCR-based molecular markers and facilitating the utilization of these genes in oat breeding programs. [ABSTRACT FROM AUTHOR]