## 4 Discussion

Table 3: List of SNP markers significantly associated with stripe rust resistance to both races _Pstv-37_ and _Pstv-40_ of _Puccinia striiformis_ f. sp. _ttiici_. Landraces and crop wild relatives are considered rich sources of new genes and alleles for traits in breeding programs given their high level of genetic diversity [39]. In this investigation, about one half of the evaluated landraces showed a range of responses from resistant to moderately resistant to both _Pst_ races (Figure 1). Although most of the durum landraces included in this work were sampled from Iran, several others collected from Italy (5 samples), Portugal (1 sample), Argentina (1 sample), and Iraq (1 sample) also were resistant or moderately resistant to races _Pstv-37_ and _Pstv-40_ (Table 1). Genetic diversity is a key requirement in any breeding program. Thus, estimation of the extent of genetic diversity and evaluation of natural population structure are important parameters for initiating genetic studies and utilizing plant genetic resources in breeding programs [40]. Population structure is an important factor for association analysis [41]. The results from STRUCTURE analysis using SNP data indicated that the durum panel was comprised of five sub-groups (Figure 2) and that 17 accessions (12%) showed a level of admixture. The grouping of the durum landraces into subpopulations was not in accordance with their geographic origins. Previously, [PERSON] et al. [22] reported a high level of molecular and morphological diversity in durum germplasm from Iran. In a study conducted by [PERSON] et al. [42], a high level of genetic diversity was found using SNP data in a durum wheat population. In an investigation of genetic diversity within a global set of durum landraces, [PERSON] et al. [43] reported a high level of genetic variability using SNP markers. After revealing a high level of genetic variability in the durum panel, we used a MLM model to incorporate population structure results with phenotypic data in the GWAS analysis to reduce false positive errors [44]. Based on the Q-Q plot, false positive associated markers could be successfully minimized in the association analysis of stripe rust reactions. Linkage disequilibrium (LD) is an important factor in the determination of the power of GWAS. In the present study, LD values were estimated for all chromosomes of the two sub-genomes A and B (Table 2). Like other studies, we found more rapid decay of LD in the A sub-genome compared to the B and D sub-genomes [23; 45; 46; 47]. Based on a total of 6642 SNP markers, 230 significant associations were found for reaction to _Pst_ races _Pstv-37_ and _Pstv-40_. Most of the associated markers for reaction to race _Pstv-37_ were located on the B genome, while most for reaction to race _Pstv-40_ were positioned on the A genome (Table S1). A recent meta-QTL analysis revealed that most stripe rust resistance loci are located on the B genome [48], which agrees with the results from the current study. Additionally, [PERSON] et al. [23] identified more QTLs/defense genes against stripe rust on the B genome than on the other sub-genomes of bread wheat. In another study, [PERSON] et al. [49] also reported a high number of significant marker-trait associations on different chromosomes of the B sub-genome. The \(R^{2}\) values for the detected associations were low to moderate (range of 3.7% and 17.8%). The three significant associations found with markers _IAAV5873_, _tplb0033f11_1381_ and _Tdurum_contig10100_523_ explained a high level of variation (R\({}^{2}\) values 18%, 14%, and 11%, respectively) for reaction to race _Pstv-37_ (Table S1). This may be attributed to markers capturing complex allelic interactions and/or specific alleles [50]. Among the 230 significantly associated SNP markers identified in this study, 30 conferred resistances to both _Pst_ races (Table 3). Loci conferring resistance to multiple _Pst_ races are more desirable in breeding programs.