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Fusarium head blight (FHB) or scab is a devastating disease of barley that severely reduces the yield and quality of the grain. Additionally, mycotoxins produced by the causal Fusarium species can contaminate harvested grain, resulting in food safety concerns and further economic losses. In the Upper Midwest region of the United States, Fusarium graminearum is the primary causal agent, and deoxynivalenol (DON) is the main mycotoxin associated with Fusarium infection. Deployment of resistant cultivars is an important component of an integrated strategy to manage this disease. Unfortunately, few good sources of FHB resistance have been identified from the evaluation of large collections of Hordeum germplasm. Over the past 25 years, many barley mapping populations have been developed with selected resistance sources to identify the number, chromosomal position and allelic effect of quantitative trait loci (QTL) contributing to FHB resistance and DON accumulation. To consolidate the genetic data generated from 14 mapping studies that included 22 bi‐ or tri‐parental mapping populations and three genome‐wide association (GWAS) mapping panels, a consensus map was constructed that includes 4145 SNP, SSR, RFLP and AFLP markers. A meta‐analysis based on this consensus map revealed 96 QTL for FHB resistance and 57 for DON accumulation scattered across the barley genome. Many of the QTL explained a low percentage (<10%) of variation for the traits and were often found significant in only one or a few environments in multi‐year/multi‐location field trials. Moreover, many of the FHB/DON QTL mapped to chromosomal positions coincided with various agro‐morphological traits that could influence the level of disease (e.g. heading date, height, spike density, and spike angle), raising the important question of whether the former are true resistance factors or are simply the result of pleiotropy with the latter. Considering the magnitude of effect, consistency of detection across environments and independence from agro‐morphological traits, only three of 96 QTL for FHB and five of 57 QTL for DON were considered priority targets for marker‐assisted selection (MAS). In spite of the challenge for having a limited number of useful QTL for breeding, genomic selection holds promise for increasing the efficiency of developing FHB‐resistant barley cultivars, an essential component of the overall management strategy for the disease. [ABSTRACT FROM AUTHOR]

Cultivation of common hop (Humulus lupulus L.) has increased dramatically during the past decade, with the primary growth occurring in the Pacific Northwest of the United States. A major limitation to hop production is hop powdery mildew [caused by Podosphaera macularis (Wallr.) Braun & Takam]. To date, a comprehensive evaluation of wild hop germplasm resources for resistance to hop powdery mildew has yet to be conducted. Herein, we report the first extensive powdery mildew resistance screening of 244 wild H. lupulus populations (6,732 individuals) collected from North America and Eurasia. We used an elimination screening approach by sequentially inoculating four P. macularis isolates containing virulence on all previously described R genes. We detected the presence of powdery mildew resistance to isolates representing extant pathogenic diversity in seven germplasms (UMN‐PMR‐002 Male [Reg. no. GP‐38, PI 699936], UMN‐PMR‐005 [Reg. no. GP‐39, PI 699937], UMN‐PMR‐006 Female [GP‐40, PI 699938], UMN‐PMR‐007 Male [Reg. no. GP‐41, PI 699939], UMN‐PMR‐008 [Reg. no. GP‐042, PI 699940], UMN‐PMR‐010 Male [Reg. no. GP‐43, OU 699941], UMN‐PMR‐013 Female [Reg. no. GP‐44, PI 699942]). Based upon genotypic profiling, the seven germplasms were identified in H. lupulus var. lupulus originating from Eurasia. These accessions could be used to introgress broad‐spectrum powdery mildew resistance in hop breeding programs worldwide. Core Ideas: New hop powdery mildew resistant sources were identified from wild Eurasian hops.Rootstocks of powdery mildew resistant sources were deposited in the National Plant Germplasm System.Biological sex of powdery mildew resistant germplasm was determined to aid in future breeding and genetic studies. [ABSTRACT FROM AUTHOR]

SUMMARY: The distribution of recombination events along large cereal chromosomes is uneven and is generally restricted to gene‐rich telomeric ends. To understand how the lack of recombination affects diversity in the large pericentromeric regions, we analysed deep exome capture data from a final panel of 815 Hordeum vulgare (barley) cultivars, landraces and wild barleys, sampled from across their eco‐geographical ranges. We defined and compared variant data across the pericentromeric and non‐pericentromeric regions, observing a clear partitioning of diversity both within and between chromosomes and germplasm groups. Dramatically reduced diversity was found in the pericentromeres of both cultivars and landraces when compared with wild barley. We observed a mixture of completely and partially differentiated single‐nucleotide polymorphisms (SNPs) between domesticated and wild gene pools, suggesting that domesticated gene pools were derived from multiple wild ancestors. Patterns of genome‐wide linkage disequilibrium, haplotype block size and number, and variant frequency within blocks showed clear contrasts among individual chromosomes and between cultivars and wild barleys. Although most cultivar chromosomes shared a single major pericentromeric haplotype, chromosome 7H clearly differentiated the two‐row and six‐row types associated with different geographical origins. Within the pericentromeric regions we identified 22 387 non‐synonymous SNPs, 92 of which were fixed for alternative alleles in cultivar versus wild accessions. Surprisingly, only 29 SNPs found exclusively in the cultivars were predicted to be 'highly deleterious'. Overall, our data reveal an unconventional pericentromeric genetic landscape among distinct barley gene pools, with different evolutionary processes driving domestication and diversification. Significance Statement: We have explored genetic variation in regions of the genome that have been genetically inaccessible, comparing wild progenitors with domesticated barleys. This study provides a more nuanced understanding to help in the future exploitation of breeding improvement. [ABSTRACT FROM AUTHOR]

SUMMARY: Accurate characterisation of splice junctions (SJs) as well as transcription start and end sites in reference transcriptomes allows precise quantification of transcripts from RNA‐seq data, and enables detailed investigations of transcriptional and post‐transcriptional regulation. Using novel computational methods and a combination of PacBio Iso‐seq and Illumina short‐read sequences from 20 diverse tissues and conditions, we generated a comprehensive and highly resolved barley reference transcript dataset from the European 2‐row spring barley cultivar Barke (BaRTv2.18). Stringent and thorough filtering was carried out to maintain the quality and accuracy of the SJs and transcript start and end sites. BaRTv2.18 shows increased transcript diversity and completeness compared with an earlier version, BaRTv1.0. The accuracy of transcript level quantification, SJs and transcript start and end sites have been validated extensively using parallel technologies and analysis, including high‐resolution reverse transcriptase‐polymerase chain reaction and 5'‐RACE. BaRTv2.18 contains 39 434 genes and 148 260 transcripts, representing the most comprehensive and resolved reference transcriptome in barley to date. It provides an important and high‐quality resource for advanced transcriptomic analyses, including both transcriptional and post‐transcriptional regulation, with exceptional resolution and precision. Significance Statement: We have developed BaRTv2.18, which represents the most comprehensive and resolved reference transcriptome in barley (Hordeum vulgare) to date. Novel methods are applied to analyze Iso‐seq data that accurately determine the transcripts from start to end (splice junctions, transcript start and end sites). It will prove to be an important and high‐quality resource for the barley research community to carry out advanced transcriptomic analyses, including both transcriptional and post‐transcriptional regulation, with exceptional resolution and precision [ABSTRACT FROM AUTHOR]

Winter survival is a major yield-limiting factor in winter barley grown in the Upper Midwest, where winter temperatures regularly reach-20°C or lower. Here, we tested the hypothesis that improved freezing survival is associated with smaller xylem vessel diameters as a mechanism that minimizes physical damage arising from intracellular ice formation, using leaf vasculature as a proxy trait. A second goal was to test whether such anatomical differences could be captured non-destructively via gas exchange measurements. We first identified a group of 11 winter barley genotypes that exhibited differential field winter survival. We then conducted xylem diameter measurements on the first three leaves on all genotypes in two independent experiments based on 1,188 images, in addition to leaf gas exchange measurements. Freezing-tolerant genotypes consistently exhibited significantly smaller metaxylem vessel diameters irrespective of leaf rank, and this difference was not influenced by hardening, indicating that this trait is heritable. Additionally, genotypes with smaller vasculature tended to exhibit lower stomatal conductance and transpiration rates. Our data indicate that genotypes with leaf xylem diameters smaller than 30 µm are prime donor parents and could be identified using gas exchange measurements, pointing to new phenotyping approaches to accelerate breeding for freezing survival. [ABSTRACT FROM AUTHOR]

Improving grain protein content and flour quality is an important goal for wheat (Triticum aestivum L.) breeding programs. Identification of genomic regions and markers associated with quality traits can help enrich wheat breeding germplasm with favorable alleles. This study was carried out to identify genetic loci controlling bread‐making quality traits in a nested association mapping population of 230 lines. Lines were evaluated for grain protein content and three gluten aggregation traits from the Brabender GlutoPeak instrument: peak maximum time (PMT), maximum torque (MT), and aggregation energy (AE). The strongest positive correlation was observed between AE and MT (r =.87), whereas the strongest negative correlation was between PMT and MT (r = −.46). We identified 25 quantitative trait loci (QTL) associated with these traits on 14 chromosomes, of which three QTL were common between MT and AE. Quantitative trait loci explaining the largest variations were observed for grain protein content and AE, with QTL that explained 13% of the observed variation for each trait. Nearly 62% of the discovered QTL were of medium effect, as the median percentage of observed phenotypic variation explained by the detected QTL was 7% (range of 4–13%). Based on QTL analysis and marker screening results, the populations discussed in this study are segregating for the known alleles of the high‐molecular‐weight glutenin gene Glu‐D1. As some lines have better phenotypic performance relative to the elite common parent RB07, crossing these lines with elite breeding lines can help increase the frequency of alleles contributing to improve flour quality traits. [ABSTRACT FROM AUTHOR]

Summary: Effective evaluation of millions of crop genetic stocks is an essential component of exploiting genetic diversity to achieve global food security. By leveraging genomics and data analytics, genomic prediction is a promising strategy to efficiently explore the potential of these gene banks by starting with phenotyping a small designed subset. Reliable genomic predictions have enhanced selection of many macroscopic phenotypes in plants and animals. However, the use of genomicprediction strategies for analysis of microscopic phenotypes is limited. Here, we exploited the power of genomic prediction for eight maize traits related to the shoot apical meristem (SAM), the microscopic stem cell niche that generates all the above‐ground organs of the plant. With 435 713 genomewide single‐nucleotide polymorphisms (SNPs), we predicted SAM morphology traits for 2687 diverse maize inbreds based on a model trained from 369 inbreds. An empirical validation experiment with 488 inbreds obtained a prediction accuracy of 0.37–0.57 across eight traits. In addition, we show that a significantly higher prediction accuracy was achieved by leveraging the U value (upper bound for reliability) that quantifies the genomic relationships of the validation set with the training set. Our findings suggest that double selection considering both prediction and reliability can be implemented in choosing selection candidates for phenotyping when exploring new diversity is desired. In this case, individuals with less extreme predicted values and moderate reliability values can be considered. Our study expands the turbocharging gene banks via genomic prediction from the macrophenotypes into the microphenotypic space. [ABSTRACT FROM AUTHOR]

Despite representing a sizeable fraction of the canopy, very little is known about leaf sheath gas exchange in grasses. Specifically, estimates of sheath stomatal conductance, transpiration and photosynthesis along with their responses to light, CO2 and vapour pressure deficit (VPD) are unknown. Furthermore, the anatomical basis of these responses is poorly documented. Here, using barley as a model system, and combining leaf‐level gas exchange, whole‐plant gravimetric measurements, transpiration inhibitors, anatomical observations, and biophysical modelling, we found that sheath and blade stomatal conductance and transpiration were similar, especially at low light, in addition to being genotypically variable. Thanks to high abaxial stomata densities and surface areas nearly half those of the blades, sheaths accounted for up to 17% of the daily whole‐plant water use, which ‐surprisingly‐ increased to 45% during the nighttime. Sheath photosynthesis was on average 17–25% that of the blade and was associated with lower water use efficiency. Finally, sheaths responded differently to the environment, exhibiting a lack of response to CO2 but a strong sensitivity to VPD. Overall, these results suggest a key involvement of sheaths in feedback loops between canopy architecture and gas exchange with potentially significant implications on adaptation to current and future climates in grasses. In barley, abaxial sheath stomata contribute significantly to canopy gas exchange, particularly in three terms of nighttime transpiration. During the day, sheaths exhibit lower photosynthesis and water four use efficiency relative to the blades, but are sensitive to evaporative demand. [ABSTRACT FROM AUTHOR]

Summary: Circular RNAs (circRNAs) are covalently closed RNA molecules. Recent studies have shown that circRNAs can arise from the transcripts of transposons. Given the prevalence of transposons in the maize genome and dramatic genomic variation driven by transposons, we hypothesize that transposons in maize may be involved in the formation of circRNAs and further modulate phenotypic variation. We performed circRNA‐Seq on B73 seedling leaves and uncovered 2804 high‐confidence maize circRNAs, which show distinct genomic features. Comprehensive analyses demonstrated that sequences related to LINE1‐like elements (LLEs) and their Reverse Complementary Pairs (LLERCPs) are significantly enriched in the flanking regions of circRNAs. Interestingly, as the number of LLERCPs increase, the accumulation of circRNAs varies, whereas that of linear transcripts decreases. Furthermore, genes with LLERCP‐mediated circRNAs are enriched among loci that are associated with phenotypic variation. These results suggest that circRNAs are likely to be involved in the modulation of phenotypic variation by LLERCPs. Further, we showed that the presence/absence variation of LLERCPs was associated with expression variation of circRNA‐circ1690 and was related to ear height, potentially through the interplay between circRNAs and functional linear transcripts. Our first study of maize circRNAs uncovers a potential new way for transposons to modulate transcriptomic and phenotypic variations. [ABSTRACT FROM AUTHOR]

Crop improvement relies on the ability to utilize novel genetic variation. Six-rowed malting barley (Hordeum vulgare L. subsp. vulgare) developed in the US Midwest has an especially narrow genetic base. Therefore, developing strategies to widen the genetic base in barley is important for continued crop improvement. A wild barley [Hordeum vulgare L. subsp. spontaneum (K. Koch) Thell.] advanced backcross-nested association mapping (AB-NAM) population was developed to assess wild-barley-derived alleles in an elite spring six-rowed malting barley background. The 796 BC2F4:6 lines in the AB-NAM were derived from 25 wild barley accessions backcrossed to the cultivar Rasmusson. Because the AB-NAM design minimizes the deleterious and unadapted traits of the wild barley parents, the population was screened in five field environments for the agronomic traits: days to heading, height, productive tiller number (PTN), test weight, and yield. The number of loci identified ranged from two (PTN, the trait with the lowest heritability) to 19 (height). Domestication-related genes were identified for each trait, particularly the photoperiod gene Ppd-H1 for days to heading, height, and PTN and the nonbrittle Btr1/Btr2 loci for test weight and yield. Only a single variant showed beneficial variation for yield from a wild barley allele, but positive effects were identified for the other traits examined, including positive variants for test weight on chromosomes 1H and 3H. The AB-NAM population is a novel resource to map agronomically important traits associated with wild barley alleles. [ABSTRACT FROM AUTHOR]

Meiotic recombination is a major driver of genetic diversity, species evolution, and agricultural improvement. Thus, an understanding of the genetic recombination landscape across the maize ( Zea mays) genome will provide insight and tools for further study of maize evolution and improvement., Here, we used c. 50 000 single nucleotide polymorphisms to precisely map recombination events in 12 artificial maize segregating populations. We observed substantial variation in the recombination frequency and distribution along the ten maize chromosomes among the 12 populations and identified 143 recombination hot regions., Recombination breakpoints were partitioned into intragenic and intergenic events. Interestingly, an increase in the number of genes containing recombination events was accompanied by a decrease in the number of recombination events per gene. This kept the overall number of intragenic recombination events nearly invariable in a given population, suggesting that the recombination variation observed among populations was largely attributed to intergenic recombination. However, significant associations between intragenic recombination events and variation in gene expression and agronomic traits were observed, suggesting potential roles for intragenic recombination in plant phenotypic diversity., Our results provide a comprehensive view of the maize recombination landscape, and show an association between recombination, gene expression and phenotypic variation, which may enhance crop genetic improvement. [ABSTRACT FROM AUTHOR]

Barley ( Hordeum vulgare L.) possesses a large and highly repetitive genome of 5.1 Gb that has hindered the development of a complete sequence. In 2012, the International Barley Sequencing Consortium released a resource integrating whole-genome shotgun sequences with a physical and genetic framework. However, because only 6278 bacterial artificial chromosome ( BACs) in the physical map were sequenced, fine structure was limited. To gain access to the gene-containing portion of the barley genome at high resolution, we identified and sequenced 15 622 BACs representing the minimal tiling path of 72 052 physical-mapped gene-bearing BACs. This generated ~1.7 Gb of genomic sequence containing an estimated 2/3 of all Morex barley genes. Exploration of these sequenced BACs revealed that although distal ends of chromosomes contain most of the gene-enriched BACs and are characterized by high recombination rates, there are also gene-dense regions with suppressed recombination. We made use of published map-anchored sequence data from Aegilops tauschii to develop a synteny viewer between barley and the ancestor of the wheat D-genome. Except for some notable inversions, there is a high level of collinearity between the two species. The software Harv EST:Barley provides facile access to BAC sequences and their annotations, along with the barley- Ae. tauschii synteny viewer. These BAC sequences constitute a resource to improve the efficiency of marker development, map-based cloning, and comparative genomics in barley and related crops. Additional knowledge about regions of the barley genome that are gene-dense but low recombination is particularly relevant. [ABSTRACT FROM AUTHOR]

Next-generation whole-genome shotgun assemblies of complex genomes are highly useful, but fail to link nearby sequence contigs with each other or provide a linear order of contigs along individual chromosomes. Here, we introduce a strategy based on sequencing progeny of a segregating population that allows de novo production of a genetically anchored linear assembly of the gene space of an organism. We demonstrate the power of the approach by reconstructing the chromosomal organization of the gene space of barley, a large, complex and highly repetitive 5.1 Gb genome. We evaluate the robustness of the new assembly by comparison to a recently released physical and genetic framework of the barley genome, and to various genetically ordered sequence-based genotypic datasets. The method is independent of the need for any prior sequence resources, and will enable rapid and cost-efficient establishment of powerful genomic information for many species. [ABSTRACT FROM AUTHOR]

Advanced resources for genome-assisted research in barley ( Hordeum vulgare) including a whole-genome shotgun assembly and an integrated physical map have recently become available. These have made possible studies that aim to assess genetic diversity or to isolate single genes by whole-genome resequencing and in silico variant detection. However such an approach remains expensive given the 5 Gb size of the barley genome. Targeted sequencing of the m RNA-coding exome reduces barley genomic complexity more than 50-fold, thus dramatically reducing this heavy sequencing and analysis load. We have developed and employed an in-solution hybridization-based sequence capture platform to selectively enrich for a 61.6 megabase coding sequence target that includes predicted genes from the genome assembly of the cultivar Morex as well as publicly available full-length c DNAs and de novo assembled RNA-Seq consensus sequence contigs. The platform provides a highly specific capture with substantial and reproducible enrichment of targeted exons, both for cultivated barley and related species. We show that this exome capture platform provides a clear path towards a broader and deeper understanding of the natural variation residing in the m RNA-coding part of the barley genome and will thus constitute a valuable resource for applications such as mapping-by-sequencing and genetic diversity analyzes. [ABSTRACT FROM AUTHOR]

Fusarium head blight, caused by Fusarium graminearum, is a devastating disease of wheat. We developed near-isogenic lines ( NILs) differing in the two strongest known F. graminearum resistance quantitative trait loci ( QTLs), Qfhs.ndsu- 3BS (also known as resistance gene Fhb1) and Qfhs.ifa- 5A, which are located on the short arm of chromosome 3B and on chromosome 5A, respectively. These NILs showing different levels of resistance were used to identify transcripts that are changed significantly in a QTL-specific manner in response to the pathogen and between mock-inoculated samples. After inoculation with F. graminearum spores, 16 transcripts showed a significantly different response for Fhb1 and 352 for Qfhs.ifa- 5A. Notably, we identified a lipid transfer protein which is constitutively at least 50-fold more abundant in plants carrying the resistant allele of Qfhs.ifa- 5A. In addition to this candidate gene associated with Qfhs.ifa- 5A, we identified a uridine diphosphate ( UDP)-glycosyltransferase gene, designated TaUGT12887, exhibiting a positive difference in response to the pathogen in lines harbouring both QTLs relative to lines carrying only the Qfhs.ifa- 5A resistance allele, suggesting Fhb1 dependence of this transcript. Yet, this dependence was observed only in the NIL with already higher basal resistance. The complete cDNA of TaUGT12887 was reconstituted from available wheat genomic sequences, and a synthetic recoded gene was expressed in a toxin-sensitive strain of Saccharomyces cerevisiae. This gene conferred deoxynivalenol resistance, albeit much weaker than that observed with the previously characterized barley HvUGT13248. [ABSTRACT FROM AUTHOR]

Previous studies have shown that there is considerable population structure in cultivated barley (Hordeum vu/gare 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. [ABSTRACT FROM AUTHOR]

Restoration of native plant communities requires adapted germplasm; thus, information is needed to guide native seed collection and production. Analysis of genetic variation has potential to provide insight into diversity and relatedness of natural populations. Our objectives were to examine genetic diversity of native species in Minnesota to discover if variation is related to biomes or distance, and possibly to develop seed collection zones. Our study included prairie cordgrass (Spartina pectinata), purple prairie clover (Dalea purpurea), and spotted joe-pye weed (Eupatorium maculatum). Using amplified fragment length polymorphisms, we analyzed 100 samples from eight populations for prairie cordgrass, 152 samples from nine populations for purple prairie clover, and 127 samples from 10 populations for spotted joe-pye weed. We found moderate to high levels of genetic diversity within each species. Small populations were not necessarily lower in diversity than larger ones. Analysis of molecular variance results indicate clear population differentiation. However, rather than displaying geographic or ecological associations, the variation had discontinuous patterns. Therefore, we were not able to develop unambiguous recommendations for seed collection. We discuss the applicability of molecular markers in detecting adaptive potential. [ABSTRACT FROM AUTHOR]

Two large-scale ethylmethanesulfonate (EMS) mutant populations from barley (Hordeum vulgare L.) cv. Optic have been developed to promote both forward and reverse genetics in this crop. Leaf material and seed from approximately 20 000 M2 plants were individually harvested, freeze-dried and archived. DNA was isolated from 9216 plants from the 20 and 30 mivi EMS treatments and assembled into 1152 eight-plant pools. To facilitate PCR-based mutation scanning an approach has been employed that combines cleavage of heteroduplexes using the Cel nuclease (Cell), post-cleavage intercalating dye labeling and the subsequent detection of cleaved products on a Transgenomic WAVE-HS. The populations were evaluated by screening for induced mutations in two genes of interest and the induced mutations were validated by sequence analysis. To enhance the screening process, 12–16 M3M progeny from each of the M2 plants were assessed for visible phenotypes and the data entered into a web accessible database (http://bioinf.scri.sari.ac.uk/distilling/distilling.html). [ABSTRACT FROM AUTHOR]

Kernel color and grain protein concentration (GPC) are two of the most important attributes of barley (Hordeum vulgate L.) grain intended for use in malting and brewing. Grain with protein levels that are too low or high or that have dark kernel color, which may result from the disease complex of kernel discoloration (KD), is unacceptable for the malting and brewing industries. The purpose of this study was to use molecular markers to map quantitative trait loci (QTLs) for KD and GPC in two recombinant inbred line (RIL) populations. One population was created by means of the high GPC and KD resistant cultivar Chevron. The other population was created from a KD resistant cultivar MNBrite that was derived from Chevron through eight generations of crossing and selection for bright kernels. The traits KD and GPC were evaluated in four and three environments, respectively, using the Chevron population and six environments using the MNBrite population. GPC and KD score were negatively correlated in both populations. A revised genetic map for the Chevron/M69 population, with an additional 45 simple sequence repeat (SSR) markers, was used to identify nine QTLs associated with KD on chromosomes 1(7H), 2(2H), 4(4H), 6(6H), and 7(5H), including two major QTLs on chromosome 6(6H). A single QTL for GPC identified in the Chevron mapping population, accounting for over 55% of the phenotypic variation, was located on chromosome 6(6H) and was coincident with one of the two major QTLs for KD. In this region, the Chevron allele increased GPC and decreased KD score. In the MNBrite mapping population, the same region of chromosome 6(6H) was mapped with SSR markers, and QTL analysis verified that this region was associated with both KD and GPC, indicating that MNBrite inherited this region of chromosome 6(6H) from Chevron. The results of this study suggest that if GPC and KD are controlled by tightly linked genes, then it should be possible to use SSR markers to identify recombinants in this region of chromosome 6(6H) and break the linkage to allow selection for KD resistance without high GPC. Alternatively, if GPC and KD are conditioned by the same gene, then it should be possible to select for KD resistance from Chevron by means of SSR markers and to use phenotypic selection to introgress other genes to reduce GPC to acceptable levels. [ABSTRACT FROM AUTHOR]