Population Structure, Linkage Disequilibrium, and Genetic Diversity in Soft Winter Wheat Enriched for Fusarium Head Blight Resistance

The occurrence of epidemics of Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, in U. S. winter wheat (Triticum aestivum L.) during the past two decades led to significant emphasis on development of resistant cultivars. Understanding the genetic diversity, population structure (PS), and linkage disequilibrium (LD) in winter wheat in the eastern United States is important for marker-assisted breeding and association analysis in this germplasm. Lines selected from collaborative FHB screening nurseries were genotyped with simple sequence repeat (SSR), sequence tagged site (STS), and Diversity Array Technology (DArT) markers to assess LD, genetic diversity, and PS. The genomewide average of LD decay to r(2) < 0.2 was 9.9 cM and moderate levels of LD (r(2) > 0.2) were generally constrained to markers less than 5 cM apart. Although the lines evaluated were targeted to distinct production zones of the eastern winter wheat region, cluster and principal component analyses did not detect separation of lines into subpopulations. The short, intense breeding history for scab resistance may have localized effects on LD. Lack of subgroups within our population could be due to intercrossing among common resistant parents and indicate frequent admixture and germplasm exchange among U. S. winter wheat programs focused on development of FHB resistant cultivars.