Association Mapping of Quantitative Trait Loci in Spring Wheat Landraces Conferring Resistance to Bacterial Leaf Streak and Spot Blotch

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa (Smith et al.) Bragard et al., and spot blotch (SB), caused by Cochliobolus sativus (S. Ito & Kurib.) Drechs. ex Dastur, are two emerging diseases of wheat (Triticum aestivum L.). To achieve sustainable disease management strategies and reduce yield losses, identifying new genes that confer quantitative resistance would benefit resistance breeding efforts. The main objective of this study was to use association mapping (AM) with 832 polymorphic Diversity Arrays Technology (DArT) markers to identify genomic regions associated with resistance to BLS and SB in 566 spring wheat landraces. From data analysis of this diverse panel of wheat accessions, we discovered five novel genomic regions significantly associated with resistance to BLS on chromosomes 1A, 4A, 4B, 6B, and 7D. Similarly, four genomic regions were found to be associated with resistance to SB on chromosomes 1A, 3B, 7B, and 7D. A high degree of linkage disequilibrium (LD) decayed over short genetic distance in the set of wheat accessions studied, and some of these genomic regions appear to be involved in multiple disease resistance (MDR). These results suggest that the AM approach provides a platform for discovery of resistance conditioned by multiple genes with quantitative effects, which could be validated and deployed in wheat breeding programs.