Novel resistance loci for quantitative resistance to Septoria tritici blotch in Asian wheat (Triticum aestivum) via genome-wide association study

Abstract Septoria tritici blotch (STB), caused by the ascomycete fungus Zymoseptoria tritici, poses severe challenges to wheat cultivation worldwide. Deployment of resistant cultivars renders a practical way to control this disease. Therefore, the identification of resistant sources and genes/QTLs is imperative. We attempted to elucidate the genomic architecture for adult-plant STB resistance in a Septoria Association Mapping Panel (SAMP), which has 181 cultivars and advanced breeding genotypes from bread wheat breeding programs in India and Bangladesh. Field experiments identified several accessions such as BGD52 (CHIR7/ANB//CHIR1), BGD54 (CHIR7/ANB//CHIR1), IND92 (WH 1218), IND8 (DBW 168) and IND75 (PBW 800) possessing high levels of resistance. Genetic analysis indicated 21 stable quantitative trait nucleotides (QTNs) for STB resistance on all wheat chromosomes except 2D, 3A, 3D, 4A, 4D, 5D, 6B, 6D and 7A, most of which were found on previously identified chromosome regions for STB resistance. Three QTNs exhibited bigger phenotypic effects and were identified in all three experiments, including Q.STB.5A.1, Q.STB.5B.1and Q.STB.5B.3. Additionally, QTNs on chromosomes 1A (Q.STB.1A.1), 2A (Q.STB_DH.2A.1, Q.STB.2A.3), 2B (Q.STB.2B.4), 5A (Q.STB.5A.1, Q.STB.5A.2) and 7B (Q.STB.7B.2) might represent novel resistance QTL. The resistant genotypes and molecular markers identified in the present study could be used for STB resistance breeding programmes around the globe. Background Septoria tritici blotch (STB) disease causes yield losses of up to 50 per cent in susceptible wheat cultivars and can pose serious threat to wheat production. In this study, genomic architecture for adult-plant STB resistance in a Septoria Association Mapping Panel (SAMP) having 181 cultivars and genomic regions governing STB resistance in a South Asian wheat panel were looked for. Results The study found STB resistance sources, genomic regions, QTLs, haplotypes, pleiotropic SNPs, and candidate genes in Asian bread wheat genotypes. Five of the discovered QTNs i.e. on chromosomes 1A (Q.STB.1A.1), 2A (Q.STB_DH.2A.1, Q.STB.2A.3), 2B (Q.STB.2B.4), 5A (Q.STB.5A.1, Q.STB.5A.2) and 7B (Q.STB.7B.2) were potentially unique. Conclusion Our findings demonstrate the importance of Asian bread wheat as a source of STB resistance alleles and novel stable QTNs for wheat breeding initiatives to generate durable and broad-spectrum Z. tritici-resistant wheat cultivars.