LOCI RELEVANT FOR YELLOW RUST RESISTANCE IN DURUM WHEAT ADAPTED TO THE MEDITERRANEAN ENVIRONMENTS IDENTIFIED IN CULTIVARS AND LANDRACES GERMPLASM THROUGH GENOME-WIDE ASSOCIATION STUDY

Yellow rust (YR), caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating fungal disease posing a significant threat to global wheat production. A genetic survey for loci controlling resistance in tetraploid wheat germplasm was carried out based on the Global Durum Panel (GDP, Mazzucotelli et al., 2020) and Tetraploid Global Collection (TGC), comprising 500 cultivars and 200 landraces and 1200 landraces, respectively. Panels were evaluated in a multienvironmental field survey for infection type (IT) and disease severity (SEV) including 12 different environments across the Mediterranean area and Argentina (2019–2021). Broad-sense heritability was consistently higher than 60% in all environments for IT and SEV. Principle component analysis (PCA) identified a few major environmental clusters, indicating similar selection pressures. In GDP, GWAS identified eight main YR resistance loci in cultivars on chromosomes 1A, 1B (three QTLs), 4B, 5A, 5B and 7B. QYr.ubo-1B.2, QYr.ubo-1B.3, QYr.ubo-5A.1, QYr.ubo-5B.1, QYr.ubo-7B.1 overlapped with significant regions detected in TGC landraces as well. Additionally, other promising YR resistance QTLs with medium-low effect were detected in TGC on all the other chromosomes. In GDP, the most impactful QTL (QYr.ubo-1B.1) mapped to a 3.4 cM region (~167Mb) on chromosome 1B was significantly associated with resistance in six single environments, with multi-environmental analyses exhibiting the highest r2=15.81%. Population structure analysis revealed higher resistance in Q4 (Italy-Valnova), Q6-7-8 (CIMMYT-SVEVO, CIMMYT’70 and CIMMYT’80), whereas Q1-2 (NorthAmerica-France and Evolutionary population from INRAE) and Q3 (ICARDA-dry) displayed higher susceptibility. Preliminary investigations validated the QTL identification, indicating that QYr.ubo-1B.1 likely coincides with the known resistance genes Yr64,Yr65, Yr24/Yr26/YrCH42, QYr.ubo-7B.1 with Yr67 (previously YrC591) and QYr.ubo-1B.3 with Yr29. In TGC, QYr.ubo-7B.1 showed the highest r2 (9.60%) and was detected in 5 environments other than both environmental clusters, which overlapped with another relevant “hotspot” of Yr loci previously mapped, namely, Yr6, Yr67, YrZH84 and Yr59. KASP® markers are used to functionally characterize genes within the identified QTL intervals, and recent progress including potential cloning of QYr.ubo.1B.1 and QYr.ubo-7B.1 will be presented.