A map of the barley genome consisting of 295 loci was constructed. These loci include 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism (SAP) markers. The RFLP-identified loci include 63 that were detected using cloned known function genes as probes. The map covers 1,250 centiMorgans (cM) with a 4.2 cM average distance between markers. The genetic lengths of the chromosomes range from 124 to 223 cM and are in approximate agreement with their physical lengths. The centromeres were localized to within a few markers on all of the barley chromosomes except chromosome 5. Telomeric regions were mapped for the short (plus) arms of chromosomes 1, 2 and 3 and the long (minus) arm of chromosomes 7.

No abstract

Winterhardiness in cereals is the consequence of a number of complex and interacting component characters: cold tolerance, vernalization requirement, and photoperiod sensitivity. An understanding of the genetic basis of these component traits should allow for more-effective selection. Genome map-based analyses hold considerable promise for dissecting complex phenotypes. A 74-point linkage map was developed from 100 doubled haploid lines derived from a winter x spring barley cross and used as the basis for quantitative trait locus (QTL) analyses to determine the chromosome location of genes controlling components of winterhardiness. Despite the greater genome coverage provided by the current map, a previously-reported interval on chromosome 7 remains the only region where significant QTL effects for winter survival were detected in this population. QTLs for growth habit and heading date, under 16 h and 24 h light, map to the same region. A QTL for heading date under these photoperiod regimes also maps to chromosome 2. Contrasting alleles at these loci interact in an epistatic fashion. A distinct set of QTLs mapping to chromosomes 1, 2, 3, and 5 determined heading date under 8 h of light. Under field conditions, all QTLs identified under controlled environment conditions were determinants of heading date. Patterns of differential QTL expression, coupled with additive and additive x additive QTL effects, underscore the complexity of winterhardiness. The presence of unique phenotype combinations in the mapping population suggests that coincident QTLs for heading date and winter survival represent the effects of linkage rather than pleiotropy.

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.

Genetic study of β-glucan content and β-glucanase activity has been facilitated by recent developments in quantitative trait loci (QTL) analysis. QTL for barley and malt β-glucan content and for green and finished malt β-glucanase activity were mapped using a 123-point molecular marker linkage map from the cross of Steptoe/Morex. Three QTL for barley β-glucan, 6 QTL for malt β-glucan, 3 QTL for β-glucanase in green malt and 5 QTL for β-glucanase in finished malt were detected by interval mapping procedures. The QTL with the largest effects on barley β-glucan, malt βglucan, green malt β-glucanase and finished malt βglucanase were identified on chromosomes 2,1,4 and 7, respectively. A genome map-based approach allows for dissection of relationships among barley and malt βglucan content, green and finished malt β-glucanase activity, and other malting quality parameters.

Quantitative trait loci (QTL) controlling traits associated with winterhardiness in barley (field survival, LT50, growth habit, and crown fructan content) were mapped to chromosome 7 in a population of 100 F1-derived doubled haploid lines. The largest QTL effects for all traits were detected in a 21% recombination interval on the long arm of chromosome 7. QTL in this region accounted for 37-68% of the variation for three measures of cold tolerance, 47% of the variation for growth habit, and 28% of the variation in crown fructan content. Trait association may be due to linkage rather than pleiotropy.

Nitrogen uptake and metabolism are central for vegetative and reproductive plant growth. This is reflected by the fact that nitrogen can be remobilized and reused within a plant, and this process is crucial for yield in most annual crops. A population of 146 recombinant inbred barley lines (F(8) and F(9) plants, grown in 2000 and 2001), derived from a cross between two varieties differing markedly in grain protein concentration, was used to compare the location of QTL associated with nitrogen uptake, storage and remobilization in flag leaves relative to QTL controlling developmental parameters and grain protein accumulation. Overlaps of support intervals for such QTL were found on several chromosomes, with chromosomes 3 and 6 being especially important. For QTL on these chromosomes, alleles associated with inefficient N remobilization were associated with depressed yield and higher levels of total or soluble organic nitrogen during grain filling and vice versa; therefore, genes directly involved in N recycling or genes regulating N recycling may be located on these chromosomes. Interestingly, the most prominent QTL for grain protein concentration (on chromosome 6) did not co-localize with QTL for nitrogen remobilization. However, QTL peaks for nitrate and soluble organic nitrogen were detected at this locus for plants grown in 2001 (but not in 2000). For these, alleles associated with low grain protein concentration were associated with higher soluble nitrogen levels in leaves during grain filling; therefore, gene(s) found at this locus might influence the nitrogen sink strength of developing barley grains.

Conversion of amplified fragment length polymorphisms (AFLPs) to sequence-specific PCR primers would be useful for many genetic linkage applications. We examined 21 wheat nullitetrasomic stocks and five wheat-barley addition lines using twelve and fourteen AFLP EcdBJJMsel primer combinations, respectively. On average, 36.8% of the scored AFLP fragments in wheat nullitetrasomic stocks and 22.3% in wheat-barley addition lines could be mapped to specific chromosomes, providing approximately 461 chromosome specific AFLP markers in wheat nullitetrasomic stocks and 174 in wheat-barley addition lines. Ten AFLP fragments specific to barley chromosomes and sixteen AFLP fragments specific to wheat 3BS and 4BS chromosome arms were isolated from the polyacrylamide gels, reamplified, cloned and sequenced. Primer sets were designed from these sequences. Amplification of wheat and barley genomic DNA using the barley-derived primers revealed that three primer sets amplified DNA from the expected chromosome, five amplified fragments from all barley chromosomes but not from wheat, one amplified a similar sized fragment from multiple barley chromosomes and from wheat, and one gave no amplification. Amplification of wheat genomic DNA using the wheat-derived primer sets revealed that three primer sets amplified a fragment from the expected chromosome, eleven primer sets amplified a similar-sized fragment from multiple chromosomes, and two gave no amplification. We also examined 21 wheat nullitetrasomic stocks using seven methylation sensitive PstHMseI primer combinations. 21.3% of the scored hypomethylated AFLP fragments in wheat nullitetrasomic stocks could be mapped to specific chromosomes. Out of