Mapping QTLs for Partial Resistance to Zymoseptoria tritici in Durum Wheat

Zymoseptoria tritici severely affects durum wheat production in the Mediterranean Basin. The high genome plasticity of the pathogen and low heritability hinder the improvement of resistance in the elite germplasm. The identification of Quantitative Trait Loci (QTLs) for partial resistance via association mapping (AM) would allow for the application of marker-assisted selection to improve resistance. A germplasm collection of 183 durum accessions suitable for AM (Maccaferri et al. 2006) was evaluated in field trials in Tunisia (Beja), Mexico (Toluca) and Italy (Argelato and Ferrara) as well as under controlled conditions with single spore isolates of Z. tritici. Though none of the identified loci conferred complete resistances, 12 significant marker-trait associations were identified, the most valuable ones (maximum R² value up to 15%) being located on chromosomes 1BL, 2AL and 4AL. Additionally, two recombinant inbred line mapping populations: Kofa (highly susceptible) × Svevo (partial resistant) and Simeto × Levante were evaluated and major QTLs were identified on chr. 1B, 4B (KS population) and in chr. 6B (SL population). Some of the identified QTLs co-located with known Stb loci previously found in hexaploid wheat. While these loci confer complete resistance in the hexaploid wheat germplasm, only partial resistance can be observed in the T. durum. Possible reasons are the presence of major susceptibility factors and increased virulence of Z. tritici strains. All mapping materials are being genotyped with the wheat Illumina 90k SNP array in order to gain a better resolution in QTL mapping and identify additional markers suitable for MAS.