Cereal crops such as wheat and maize have large repeat-rich genomes that make cloning of individual genes challenging. Moreover, gene order and gene sequences often differ substantially between cultivars of the same crop species. A major bottleneck for gene cloning in cereals is the generation of high-quality sequence information from a cultivar of interest. In order to accelerate gene cloning from any cropping line, we report 'targeted chromosome-based cloning via long-range assembly' (TACCA). TACCA combines lossless genome-complexity reduction via chromosome flow sorting with Chicago longrange linkage to assemble complex genomes. We applied TACCA to produce a high-quality (N50 of 9.76 Mb) de novo chromosome assembly of the wheat line CH Campala Lr22a in only 4 months. Using this assembly we cloned the broad-spectrum Lr22a leaf-rust resistance gene, using molecular marker information and ethyl methanesulfonate (EMS) mutants, and found that Lr22a encodes an intracellular immune receptor homologous to the Arabidopsis thaliana RPM1 protein.DOI: https://doi.org/10.1038/nbt.3877Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-144182 Journal Article Accepted Version Originally published at: Thind, Anupriya Kaur; Wicker, Thomas; Šimková, Hana; Fossati, Dario; Moullet, Odile; Brabant, Cécile; Vrána, Jan; Doležel, Jaroslav; Krattinger, Simon G (2017). Rapid cloning of genes in hexaploid wheat using cultivar-specific long-range chromosome assembly. Nature Biotechnology, 35(8) Using this assembly we cloned the broad-spectrum Lr22a leaf-rust resistance gene using molecular marker information and EMS mutants and found that Lr22a encodes an intracellular immune receptor homologous to the Arabidopsis RPM1 protein.While the world population continues to grow, the arable land per capita is decreasing 6 . To ensure food security, agriculture will require high-yielding crops that can withstand diseases, pests and adverse climatic conditions. A better understanding of genes that control these important traits may enable breeding of crop cultivars capable of feeding the 9-10 billion people expected by 2050. triticina isolates [13][14][15][16] . The Lr22a-mediated resistance is not present in young seedlings (<20 days) but is only visible in wheat plants from ~25 days of age.First, in order to evaluate the effectiveness of Lr22a against Swiss P. triticina isolates we inoculated the Lr22a-containing backcross line RL6044 ('Thatcher Lr22a') and the spring wheat cultivar 'Thatcher' with ten P. triticina isolates that were collected in Switzerland. The first leaves of RL6044 developed leaf rust pustules of similar size as the susceptible control 'Thatcher', while we observed complete to moderate resistance on the third leaves of 30-dayold RL6044 plants in comparison to 'Thatcher' (Fig. 1, Supplementary Fig. 1).Lr22a was previously mapped to the short arm of wheat chromosome 2D using microsatellite analysis of the Lr22a-containing wheat line 98B34-T4B 13 . In order to...

Association mapping in populations relevant for wheat breeding has a large potential for validating and fine-mapping QTLs identified in F2- or DH (double haploid)-derived populations. In this study, associations between markers in the region of QSng.sfr-3BS, a major QTL for resistance to Stagonospora nodorum glume blotch (SNG), and SNG resistance were investigated by linkage and association analyses. After increasing marker density in 240 F(5:7) recombinant inbred lines (RILs), QSng.sfr-3BS explained 43% of the genetic variance and peaked 0.6 cM proximal from the marker SUN2-3B. Association between SNG resistance and markers mapped in the region of QSng.sfr-3BS was investigated in a population of 44 modern European winter wheat varieties. Two genetically distinct subpopulations were identified within these lines. In agreement with linkage analyses, association mapping by a least squares general linear model (GLM) at marker loci in the region of QSng.sfr-3BS revealed the highest association with SNG resistance for SUN2-3B (p < 0.05). Association mapping can provide an effective mean of relating genotypes to complex quantitative phenotypes in hexaploid wheat. Linkage disequilibrium (r (2)) in chromosome 3B extended less than 0.5 cM in 44 varieties, while it extended about 30 cM in 240 RILs, based on 91 SSR and STS marker-pair comparisons. This indicated that the association mapping population had a marker resolution potential at least 390-fold higher compared to the RIL population.

Stagonospora nodorum is the causal agent of the Stagonospora glume blotch disease in hexaploid wheat. The Swiss winter bread wheat cv. 'Arina' has a highly effective, durable and quantitative glume blotch resistance. We studied 240 single seed descent (SSD)-derived lines of an 'Arina x Forno' F(5:7) population to identify and map quantitative trait loci (QTLs) for glume blotch resistance under natural infestation. Using composite interval mapping (CIM) and LOD>4.5, we detected two chromosomal regions on chromosome arms 3BS and 4BL which were specifically associated with glume blotch resistance. These identified QTLs were designated QSng.sfr-3BS and QSng.sfr-4BL, respectively. QSng.sfr-3BS peaked at the locus Xgwm389 in the telomeric region of the short arm of chromosome 3B and explained 31.2% of the observed phenotypic variance for the resistance within the population. The responsible QSng.sfr-3BS allele originated from the resistant parent 'Arina'. The QTL QSng.sfr-4BL (19.1%) mapped to chromosome arm 4BL ('Forno' allele) very close to two known genes, TaMlo and a catalase ( Cat). Both QTL alleles combined could enhance the resistance level by about 50%. Additionally, they showed significant epistatic effects (4.4%). We found PCR-based microsatellite markers closely linked to QSng.sfr-3BS (gwm389) and QSng.sfr-4BL (gwm251) which make marker-assisted selection (MAS) for Stagonospora glume blotch resistance feasible. We also found one resistance QTL, QSng.sfr-5BL, on the long arm of chromosome 5B which overlapped with QTLs for plant height as well as heading time.

Breeding for enhanced rooting depth and root biomass in deeper soil layers is a promising strategy to adapt wheat (Triticum aestivum L.) plants to drought periods. We evaluated (1) the extent of indirect selection of root traits during the last century of wheat breeding and (2) how it affected the variety performance under well-watered conditions compared to gradually developing drought stress. Fourteen bread wheat genotypes covering 100 years of Swiss wheat breeding were grown in 1.6 m tall columns in the greenhouse under well-watered and drought conditions. Root parameters, such as rooting depth and root biomass and above ground parameters were determined at flowering and maturity. Rooting depth showed a negative trend in response to year of release under well-watered conditions but not under early water stress. Modern varieties responded with enhanced root allocation to deeper soil layers. Consequently, rooting depth was positively correlated with plant height at well-watered conditions but not under early water stress. Considerable genetic variation for rooting depth among modern varieties indicates that the trait is selectable without strong alteration of plant height. We conclude that modern varieties adjusted rooting depth to water demand.

Little has been published about the composition of mineral elements in triticale (× Triticosecale Wittm.) grains. Our study deals with the following questions: (i) How do increases in grain yield, resulting from growing triticale in more productive environments or growing more productive cultivars, affect the concentrations of minerals in the grains? (ii) Do genotypes exist whose grains are exceptionally high or low in minerals? (iii) To what extent are the concentrations of protein and minerals related? To answer these questions, 10 hexaploid winter triticale lines/cultivars were grown at three locations in western Switzerland for 2 yr. Whole grains were analyzed for protein (N ✕ 5.7), P, K, Mg, Ca, Fe, Mn, Zn, and Cu. With the exception of Mn and Zn, the variation in mineral element concentrations among lines/cultivars was as great as or greater than the variation caused by environmental factors. Except for Mg, concentrations of mineral elements were significantly lower in the year in which the grain yield was higher. Except for Ca, high grain yields of cultivars were associated with low concentrations of minerals, indicating that one‐sided selection for high grain yield tends to reduce the nutritional quality of triticale grain. Concentrations of protein and minerals were positively correlated, suggesting that breeding for elevated levels of protein is likely to increase the concentrations of minerals.