Genome-wide association and biparental mapping revealed a major quantitative trait locus associated with seedling resistance to bacterial leaf streak in durum

We identified sources of resistance and a major QTL for resistance to bacterial leaf streak in durum. Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa, has reemerged as a significant disease impacting bread wheat and durum production worldwide. The lack of resistance sources and limited understanding of the genetics behind host resistance have made breeding for BLS resistance challenging, especially in durum wheat. In this study, we first evaluated the reaction of a set of durum cultivars, mainly from North Dakota State University (NDSU). Our results indicated that most cultivars were susceptible, with only a few exceptions. Next, we utilized a subset of the Global Durum Panel (GDP) to identify sources of resistance and conduct a genome-wide association study (GWAS) to identify BLS resistance loci. Additionally, we performed disease evaluations and quantitative trait locus (QTL) analysis on two durum recombinant inbred line (RIL) populations: one was derived from the resistant NDSU cultivar 'Ben' and the other from the resistant Ethiopian landrace PI 387336. Our findings revealed that several modern durum cultivars from different countries within the GDP exhibited a high level of resistance. Both GWAS and biparental mapping identified a major QTL located at the distal end of chromosome arm 6AS. The physical positions of the single-nucleotide polymorphism (SNP) markers obtained from both experiments strongly suggest that the same locus is responsible for BLS resistance in the tested durum materials. The resistant accessions and SNP markers identified in this study will be valuable for transferring this major QTL into elite durum and common wheat cultivars.