Molecular Mapping and Validation of Race Non-Specific Powdery Mildew Resistance Loci in Wheat cv Naxos with High-Density SNP Markers

The German spring wheat cultivar ‘Naxos’ has shown high levels partial resistance to powdery mildew at the adult plant stage and the absence of race-specific resistance at the seedling stage. QTL mapping in the SHA3/CBRD x Naxos population identified resistance loci with stable effects across environments on 1AS and 2DL and two minor loci on 2BL and 7DS (Lu et al., 2012, TAG 125: 297-309). The main objectives of the present study were to validate the powdery mildew resistance QTL from ‘Naxos’ in new genetic backgrounds and identify tightly linked SNP markers for powdery mildew resistance breeding. One F₆ RIL population from the cross SORU#1 x Naxos was evaluated in hillplot nurseries over two years (2012 and 2013) at two locations (Hamar and Ås) in south-eastern Norway. A total of 10,372 polymorphic SNP markers from the Illumina iSelect 90K wheat chip were used to develop linkage maps based on 131 RILs. The major QTL on 1AS and the minor QTL on 2BL reported in SHA3/CBRD x Naxos were confirmed by QTL mapping in this new population. In addition, Naxos were found to contribute QTL for powdery mildew resistance with consistent effects across environments on chromosome arms 2AL and 7BL. Additionally, SORU#1 contributed a QTL for resistance on 3AS. KASP assays were developed for the most closely linked SNP markers to the Naxos QTL on 1AS, 2AL, 2BL and 7BL, and genotyped on 140 RILs from the Avocet x Naxos population. Three of these QTL – on 1AS, 2AL and 7BL – were found to segregate and showed significant effects on powdery mildew resistance in this population. The Avoxet x Naxos population was also found to segregate for Lr46/Pm39 that tended to mask the effect fo the minor QTL on 2AL and 7BL, which were only signficant in the subpopulation lacking the resistance allele at this locus. The 1AS QTL was confirmed as a major QTL for powdery mildew resistance in Naxos, and tightly linked KASP markers were validated for use in marker-assisted selection.