Phenotypic and genetic resistance to Septoria blotch disease in European wheat varieties

Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB), poses a critical threat to wheat (Triticum aestivum L.) production in temperate Europe, underscoring the need for durable genetic resistance. Here, we screened 151 winter wheat varieties at the seedling stage using a mixed inoculum of five virulent isolates. Disease severity was quantified at 14, 21, and 28 days post-inoculation to calculate the area under the disease progress curve. We observed broad phenotypic variation, with higher susceptibility in Southern European germplasm. A genome-wide association study identified three significantly resistant loci: IWB5774 on chromosome 2D, and IWB72742 and IWB11406 on chromosome 1B. Functional annotation mapped these markers to high-priority candidate genes, including a TaBx3D-like protein, the endomembrane trafficking regulator WDR91, and NAP1, a nucleosome assembly factor involved in stress signaling. These findings provide robust molecular markers for breeding and nominate specific targets for functional validation of STB resistance mechanisms.