Haplotype diversity and population structure in cultivated and wild barley evaluated for Fusarium head blight responses

Fusarium head blight (FHB) is a threat to barley (Hordeum vulgare L.) production in many parts of the world. A number of barley accessions with partial resistance have been reported and used in mapping experiments to identify quantitative trait loci (QTL) associated with FHB resistance. Here, we present a set of barley germplasm that exhibits FHB resistance identified through screening a global collection of 23,255 wild (Hordeum vulgare ssp. spontaneum) and cultivated (Hordeum vulgare ssp. vulgare) accessions. Seventy-eight accessions were classified as resistant or moderately resistant. The collection of FHB resistant accessions consists of 5, 27, 46 of winter, wild and spring barley, respectively. The population structure and genetic relationships of the germplasm were investigated with 1,727 Diversity Array Technology (DArT) markers. Multiple clustering analyses suggest the presence of four subpopulations. Within cultivated barley, substructure is largely centered on spike morphology and growth habit. Analysis of molecular variance indicated highly significant genetic variance among clusters and within clusters, suggesting that the FHB resistant sources have broad genetic diversity. The haplotype diversity was characterized with DArT markers associated with the four FHB QTLs on chromosome 2H bin8, 10 and 13 and 6H bin7. In general, the wild barley accessions had distinct haplotypes from those of cultivated barley. The haplotype of the resistant source Chevron was the most prevalent in all four QTL regions, followed by those of the resistant sources Fredrickson and CIho4196. These resistant QTL haplotypes were rare in the susceptible cultivars and accessions grown in the upper Midwest USA. Some two- and six-rowed accessions were identified with high FHB resistance, but contained distinct haplotypes at FHB QTLs from known resistance sources. These germplasm warrant further genetic studies and possible incorporation into barley breeding programs.