Population Structure and Linkage Disequilibrium in U.S. Barley Germplasm: Implications for Association Mapping

• Published in: Crop science 2010-03, Vol.50 (2), p.556-566
• Main Authors: Hamblin, Martha T, Close, Timothy J, Bhat, Prasanna R, Chao, Shiaoman, Kling, Jennifer G, Abraham, K. Joseph, Blake, Tom, Brooks, Wynse S, Cooper, Blake, Griffey, Carl A, Hayes, Patrick M, Hole, David J, Horsley, Richard D, Obert, Donald E, Smith, Kevin P, Ullrich, Steven E, Muehlbauer, Gary J, Jannink, Jean-Luc
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; alleles; association mapping; Barley; Biological and medical sciences; chromosome mapping; Cultivation; Design; Frequency distribution; Fundamental and applied biological sciences. Psychology; gene segregation; Generalities. Genetics. Plant material; genetic distance; genetic markers; Genetic resources, diversity; Genetics; Genetics and breeding of economic plants; Genomics; genotype; Grain cultivation; Hordeum vulgare; linkage disequilibrium; Plant breeding; Plant material; population genetics; Population structure; single nucleotide polymorphism; six-row barley; Spring; Studies; two-row barley; Winter
• ISSN: 0011-183X; 1435-0653
• DOI: 10.2135/cropsci2009.04.0198

Previous studies have shown that there is considerable population structure in cultivated barley (Hordeum vulgare L.), with the strongest structure corresponding to differences in row number and growth habit. U.S. barley breeding programs include six-row and two-row types and winter and spring types in all combinations. To facilitate mapping of complex traits in breeding germplasm, 1816 barley lines from 10 U.S. breeding programs were scored with 1536 single nucleotide polymorphism (SNP) genotyping assays. The number of SNPs segregating within breeding programs varied from 854 to 1398. Model-based analysis of population structure showed the expected clustering by row type and growth habit; however, there was additional structure, some of which corresponded to the breeding programs. The model that fit the data best had seven populations: three two-row spring, two six-row spring, and two six-row winter. Average linkage disequilibrium (LD) within populations decayed over a distance of 20 to 30 cM, but some populations showed long-range LD suggestive of admixture. Genetic distance (allele-sharing) between populations varied from 0.11 (six-row spring vs. six-row spring) to 0.45 (two-row spring vs. six-row spring). Analyses of pairwise LD revealed that the phase of allelic associations was not well correlated between populations, particularly when their allele-sharing distance was >0.2. These results suggest that pooling divergent barley populations for purposes of association mapping may be inadvisable.