Septoria tritici blotch (STB) caused by Zymoseptoria tritici is one of the most important foliar diseases of wheat causing significant yield losses worldwide. In this study, a panel of bread wheat genotypes comprised 185 globally diverse genotypes were tested against 10 Z. tritici isolates at the seedling stage. Genome-wide association study (GWAS) using high-throughput DArTseq markers was performed and further gene expression analysis of significant markers trait association (MTAs) associated with resistance to STB was analyzed. Disease severity level showed significant differences among wheat genotypes for resistance to different Z. tritici isolates. We found novel landrace genotypes that showed highly resistance spectra to all tested isolates. GWAS analysis resulted in 19 quantitative trait loci (QTLs) for resistance to STB that were located on 14 chromosomes. Overall, 14 QTLs were overlapped with previously known QTLs or resistance genes, as well as five potentially novel QTLs on chromosomes 1A, 4A, 5B, 5D and 6D. Identified novel resistance sources and also novel QTLs for resistance to different Z. tritici isolates can use for pyramiding and development of durable resistance cultivars in future wheat breeding programs.

Septoria tritici blotch (STB) caused by Zymoseptoria tritici is one of the most important foliar diseases of wheat that can lead to significant yield losses worldwide. In this study, we analyzed STB resistance pattern of 185 diverse bread wheat genotypes at the seedling stage in order to confirm known resistance genes or identifying novel putative QTLs conferring resistance to STB. The phenotyping data using 10 Z. tritici isolates showed that large genetic variance exists for STB infection in wheat germplasm. Genome-wide association mapping (GWAS) using CMLM algorithm identified 37 quantitative-trait loci (QTL) for resistance to STB on 17 chromosomes. Most of QTLs overlapped with known STB resistance genes, while GWAS scan revealed several newly identified QTLs on chromosomes 4A, 5D and 6D for resistance to STB. Genome annotation of marker-trait association (MTA) against wheat reference genome revealed 29 MTAs corresponded to the putative genes, which their functional descriptions identifiers included diseases resistance proteins in plants. These MTAs and novel QTLs associated with STB resistance found here, can be used in future wheat breeding programs to recombine different loci for durable resistance to STB.