Flowering time is an important trait in wheat breeding as it affects adaptation and yield potential. The aim of this study was to investigate the genetic architecture of flowering time in European winter bread wheat cultivars. To this end a population of 410 winter wheat varieties was evaluated in multi-location field trials and genotyped by a genotyping-by-sequencing approach and candidate gene markers. Our analyses revealed that the photoperiod regulator Ppd-D1 is the major factor affecting flowering time in this germplasm set, explaining 58% of the genotypic variance. Copy number variation at the Ppd-B1 locus was present but explains only 3.2% and thus a comparably small proportion of genotypic variance. By contrast, the plant height loci Rht-B1 and Rht-D1 had no effect on flowering time. The genome-wide scan identified six QTL which each explain only a small proportion of genotypic variance and in addition we identified a number of epistatic QTL, also with small effects. Taken together, our results show that flowering time in European winter bread wheat cultivars is mainly controlled by Ppd-D1 while the fine tuning to local climatic conditions is achieved through Ppd-B1 copy number variation and a larger number of QTL with small effects.
Genomic selection models can be trained using historical data and filtering genotypes based on phenotyping intensity and reliability criterion are able to increase the prediction ability. We implemented genomic selection based on a large commercial population incorporating 2325 European winter wheat lines. Our objectives were (1) to study whether modeling epistasis besides additive genetic effects results in enhancement on prediction ability of genomic selection, (2) to assess prediction ability when training population comprised historical or less-intensively phenotyped lines, and (3) to explore the prediction ability in subpopulations selected based on the reliability criterion. We found a 5 % increase in prediction ability when shifting from additive to additive plus epistatic effects models. In addition, only a marginal loss from 0.65 to 0.50 in accuracy was observed using the data collected from 1 year to predict genotypes of the following year, revealing that stable genomic selection models can be accurately calibrated to predict subsequent breeding stages. Moreover, prediction ability was maximized when the genotypes evaluated in a single location were excluded from the training set but subsequently decreased again when the phenotyping intensity was increased above two locations, suggesting that the update of the training population should be performed considering all the selected genotypes but excluding those evaluated in a single location. The genomic prediction ability was substantially higher in subpopulations selected based on the reliability criterion, indicating that phenotypic selection for highly reliable individuals could be directly replaced by applying genomic selection to them. We empirically conclude that there is a high potential to assist commercial wheat breeding programs employing genomic selection approaches.
Improvement of end-use quality in bread wheat (Triticum aestivum L.) depends on a thorough understanding of the genetic basis of important quality traits. The main goal of our study was to investigate the genetic basis of 1,000-kernel weight, protein content, sedimentation volume, test weight, and starch concentration using an association mapping approach. We fingerprinted 207 diverse European elite soft winter wheat lines with 115 SSR markers and evaluated the genotypes in multi-environment trials. The principal coordinate analysis revealed absence of a clear population but presence of a family structure. Therefore, we used linear mixed models and marker-based kinship matrices to correct for family structure. In genome-wide scans, we detected main effect QTL for all five traits. In contrast, epistatic QTL were only observed for sedimentation volume and test weight explaining a small proportion of the genotypic variation. Consequently, our findings suggested that integrating epistasis in marker-assisted breeding will not lead to substantially increased selection gain for quality traits in soft winter wheat.
Plant height variation in European winter wheat cultivars is mainly controlled by the Rht - D1 and Rht - B1 semi-dwarfing genes, but also by other medium- or small-effect QTL and potentially epistatic QTL enabling fine adjustments of plant height. Plant height is an important goal in wheat (Triticum aestivum L.) breeding as it affects crop performance and thus yield and quality. The aim of this study was to investigate the genetic control of plant height in European winter wheat cultivars. To this end, a panel of 410 winter wheat varieties from across Europe was evaluated for plant height in multi-location field trials and genotyped for the candidate loci Rht-B1, Rht-D1, Rht8, Ppd-B1 copy number variation and Ppd-D1 as well as by a genotyping-by-sequencing approach yielding 23,371 markers with known map position. We found that Rht-D1 and Rht-B1 had the largest effects on plant height in this cultivar collection explaining 40.9 and 15.5 % of the genotypic variance, respectively, while Ppd-D1 and Rht8 accounted for 3.0 and 2.0 % of the variance, respectively. A genome-wide scan for marker–trait associations yielded two additional medium-effect QTL located on chromosomes 6A and 5B explaining 11.0 and 5.7 % of the genotypic variance after the effects of the candidate loci were accounted for. In addition, we identified several small-effect QTL as well as epistatic QTL contributing to the genetic architecture of plant height. Taken together, our results show that the two Rht-1 semi-dwarfing genes are the major sources of variation in European winter wheat cultivars and that other small- or medium-effect QTL and potentially epistatic QTL enable fine adjustments in plant height.
AAC Icefield is the first hard white winter wheat (Triticum aestivum L.) cultivar registered in western Canada. It was selected from a population of F-1-derived doubled-haploids of the cross McClintock/83W020007. Registration testing occurred from 2013 to 2017. These data, collected over 53 site -years, showed that AAC Icefield yielded significantly more grain than CDC Buteo, was similar in yield to Flourish, Moats, and CDC Falcon, and was significantly lower yielding than AAC Elevate and Sunrise. AAC Icefield expressed fair survival, intermediate maturity, short straw, and very good lodging resistance. Test weight and kernel weight were within the range of the checks. Ratings based on the prevalent disease races in western Canada were summarized as resistant to stem rust, moderately resistant to leaf and stripe rust, intermediate in resistance to Fusarium head blight, and susceptible to common bunt. The grain yield, agronomic characteristics, and disease resistance attributes of AAC Icefield provide good adaptation for all areas of western Canada. Despite lower grain protein concentration than Canada Western Red Winter wheat cultivars, AAC Icefield showed exceptional gluten strength per unit of protein. AAC Icefield is well-suited to a wide range of end-uses including white and whole-grain pan bread, French and flat breads, Asian steamed bread, and noodles. Currently designated in the Canada Western Experimental wheat class to facilitate test marketing, a decision on permanent class placement for AAC Icefield will be made by the Canadian Grain Commission following the assessment of market interest.
A powdery mildew resistance gene was introgressed from Aegilops speltoides into winter wheat and mapped to chromosome 5BL. Closely linked markers will permit marker-assisted selection for the resistance gene. Powdery mildew of wheat (Triticum aestivum L.) is a major fungal disease in many areas of the world, caused by Blumeria graminis f. sp. tritici (Bgt). Host plant resistance is the preferred form of disease prevention because it is both economical and environmentally sound. Identification of new resistance sources and closely linked markers enable breeders to utilize these new sources in marker-assisted selection as well as in gene pyramiding. Aegilops speltoides (2n = 2x = 14, genome SS), has been a valuable disease resistance donor. The powdery mildew resistant wheat germplasm line NC09BGTS16 (NC-S16) was developed by backcrossing an Ae. speltoides accession, TAU829, to the susceptible soft red winter wheat cultivar ‘Saluda’. NC-S16 was crossed to the susceptible cultivar ‘Coker 68-15’ to develop F2:3 families for gene mapping. Greenhouse and field evaluations of these F2:3 families indicated that a single gene, designated Pm53, conferred resistance to powdery mildew. Bulked segregant analysis showed that multiple simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers specific to chromosome 5BL segregated with the resistance gene. The gene was flanked by markers Xgwm499, Xwmc759, IWA6024 (0.7 cM proximal) and IWA2454 (1.8 cM distal). Pm36, derived from a different wild wheat relative (T. turgidum var. dicoccoides), had previously been mapped to chromosome 5BL in a durum wheat line. Detached leaf tests revealed that NC-S16 and a genotype carrying Pm36 differed in their responses to each of three Bgt isolates. Pm53 therefore appears to be a new source of powdery mildew resistance.
A new powdery mildew resistance gene Pm54 was identified on chromosome 6BL in soft red winter wheat.Powdery mildew is causing increasing damage to wheat production in the southeastern USA. To combat the disease, a continuing need exists to discover new genes for powdery mildew resistance and to incorporate those genes into breeding programs. Pioneer® variety 26R61 (shortened as 26R61) and AGS 2000 have been used as checks in the Uniform Southern Soft Red Winter Wheat Nursery for a decade, and both have provided good resistance across regions during that time. In the present study, a genetic analysis of mildew resistance was conducted on a RIL population developed from a cross of 26R61 and AGS 2000. Phenotypic evaluation was conducted in the field at Plains, GA, and Raleigh, NC, in 2012 and 2013, a total of four environments. Three quantitative trait loci (QTL) with major effect were consistently detected on wheat chromosomes 2BL, 4A and 6BL. The 2BL QTL contributed by 26R61 was different from Pm6, a widely used gene in the southeastern USA. The other two QTL were identified from AGS 2000. The 6BL QTL was subsequently characterized as a simple Mendelian factor when the population was inoculated with a single Blumeria graminis f. sp. tritici (Bgt) isolate in controlled environments. Since there is no known powdery mildew resistance gene (Pm) on this particular location of common wheat, the gene was designated Pm54. The closely linked marker Xbarc134 was highly polymorphic in a set of mildew differentials, indicating that the marker should be useful for pyramiding Pm54 with other Pm genes by marker-assisted selection.
Pintail is an awnless hard red winter wheat ( Triticum aestivum L.) cultivar that was registered in 2012 and is eligible for grades of Canada Western General Purpose (CWGP) wheat. It was developed using wheat x maize-pollen doubled haploid techniques. Evaluated across western Canada from 2008 to 2010 relative to CDC Harrier, CDC Falcon and CDC Ptarmigan, Pintail expressed grain yield ranging from 98.6 to 105.8% of these CWGP wheat checks. Its area of greatest adaptation was in the parkland and semi-arid prairie regions of Alberta and western Saskatchewan, where cold tolerance is a primary concern. Pintail exhibited excellent winter survival, intermediate maturity, medium height and strong straw. Test weight was within the range of the checks, and kernel weight was lower than all of the checks. Pintail displayed moderate resistance to stripe rust, moderate susceptibility to stem and leaf rust, and susceptibility to common bunt and Fusarium head blight. The high yield and awnless spike of Pintail should make it particularly attractive in various livestock feed and forage applications.
AAC Goldrush is a hard red winter wheat (Triticum aestivum L.) cultivar eligible for grades of Canada Western Red Winter wheat. It was developed using a modified pedigree breeding method. AAC Goldrush was tested in replicated trials across western Canada for 6 yr: 2 yr for initial characterization followed by 4 yr of evaluation in registration trials. Based on 41 station - years of registration trial data, AAC Goldrush yielded significantly more grain than CDC Buteo and was similar to Flourish, Moats, and AAC Elevate. AAC Goldrush expressed very good winter survival, intermediate maturity, medium height straw with good lodging resistance, and average size kernels. Disease ratings at the time of registration were resistant to the prevalent races of leaf rust, moderately resistant to stem rust, intermediate in resistance to stripe rust and Fusarium head blight, and susceptible to common bunt. Leaf spot reactions were similar to the best check. The grain yield, agronomic characteristics, and disease resistance attributes of AAC Goldrush make it particularly well-suited to the eastern Prairie region of western Canada where CDC Buteo has been popular.