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The aim of this study was to measure genetic diversity and population structure among 92 Canadian barley cultivars using two types of molecular markers (SSRs and DArTs) and pedigree data. A total of 368 alleles were identified at 50 SSR loci. The number of alleles per locus ranged between 2 and 13 ( = 7.36) and PIC values ranged from 0.34 to 0.86 ( = 0.69). For the biallelic DArT markers, the genetic distance matrix was based on 971 markers whose PIC values ranged between 0.06 and 0.50 ( = 0.39). A third distance matrix was computed based on the kinship coefficient. Clustering of genotypes was performed based on the genetic distance matrix and the three dendrograms obtained showed the genetic relationships among barley cultivars. The topological similarity of the three dendrograms was estimated using a congruence index and showed the three dendrograms to be in very good agreement. Statistical analysis also showed a highly significant correlation between the SSR and DArT matrices ( r = 0.80, p < 0.002) compared with lower yet significant correlations of the pedigree data with both marker types ( r = 0.46, p < 0.002; r = 0.52, p < 0.002). Finally, we assessed linkage disequilibrium in this germplasm and found it to be quite extensive, as the mean distance between marker pairs with significant ( P < 0.001) r2 values >0.5 was 3.8 cM. Information obtained from comparing results of different genetic diversity estimation methods should be useful for the improvement and conservation of barley genetic resources. [ABSTRACT FROM AUTHOR]

Diversity Array Technology (DArT) markers were used to investigate the genetic diversity, population structure, and extent of linkage disequilibrium (LD) on a genome-wide level in Canadian barley (Hordeum vulgare L.). Approximately 1,000 DArT markers were polymorphic and scored with high confidence among a collection of 170 barley lines composed mostly of Canadian cultivars and breeding lines. The reproducibility of DArT markers proved very high, as 99.9% of allele calls were identical among seven replicated samples. The polymorphism information content (PIC) of DArT markers ranged between 0.04 and 0.50 with an average of 0.38. Using principal coordinate analysis (PCoA), most lines fell into one of two major groups reflecting inflorescence type (two-row versus six-row). Within these two large groups, evidence of geographic clustering of genotypes was also observed. A cluster analysis Unweighted Pair Group Method with Algorithmic Mean suggested the existence of three subgroups within the two-row group and four subgroups within the six-row group. An analysis of molecular variance (AMOVA) revealed highly significant (P < 0.001) genetic variance within subgroups, among subgroups, and among groups. Values of LD, expressed as r (2), declined with increasing genetic distance, and mean values of r (2) fell below 0.2 for markers located 2.6 cM apart. Approximately 8% of marker pairs located on the same chromosome and 3.4% of pairs located on different chromosomes were in LD (r ( 2 ) > 0.2). Within both the subsets of two-row and six-row lines, LD extended slightly further (3.5 cM) than for the entire set, while 7.5% of intra-chromosomal locus pairs and <2% of inter-chromosomal pairs were in LD. We discuss the implications of these findings with regard to the prospects of association mapping of complex traits in barley.