13 ERA-CAPS BARLEY NAM - Locating exotic genes that control agronomic traits under stress in a wild barley nested association mapping (NAM) population

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Delivering sustainable food production in the face of climate change with reduced fertilizer and pesticide input requires a revolution in crop improvement. Meanwhile, modern crops are becoming increasingly depleted in gene biodiversity. Extending crop biodiversity and supporting future crop improvements can be achieved by 'mining' allelic variants of genes from ancestral wild germplasm. Novel strategies to utilize multi-parental breeding populations and apply the genomics revolution offer a promising route towards exploitation of exotic germplasm for breeding. We will test both approaches using wild barley (Hordeum vulgare ssp. spontaneum) as a model to improve agronomic performance of cultivated barley under abiotic and biotic stress conditions. For this, we will explore a nested association mapping (NAM) approach using the first cereal NAM population HEB-25 ('Halle Exotic Barley') to simultaneously test 25 wild barley accessions for beneficial gene effects. HEB-25 consists of 1,420 BC1S3 lines, each of which carrying ca. 25% of wild barley genome from one of 25 exotic donors on a 75% genetic background of the recipient spring barley cultivar Barke. First, the HEB-25 lines will be assessed for allele content, employing state-of-the-art Exome Capture with Next Generation Sequencing (EC-Seq) to discover single nucleotide polymorphisms (SNP) for 21,643 genes in each of the 1,420 HEB-25 lines. We expect to map roughly 400,000 SNPs, giving several SNPs per gene with the goal to distinguish any wild barley allele from the recipient Barke allele. Second, the HEB-25 lines will be cultivated in field trials in Germany, Scotland and Israel, to assess phenotypic stress performance under either nitrogen deficiency, drought or pathogen attack. Morphologic, agronomic, and nutrient content traits will be scored, as well as resistances against the important barley diseases leaf rust, yellow rust and net blotch. In addition, agronomic performance will be modeled in Israel by up-to-date remote sensing technology, to establish non-invasive phenotype prediction models. Third, the collected data sets will be archived and further processed in a central data warehouse at Halle, built around a custom web-accessible relational database, enabling universal access to the project outputs.Fourth, the resulting genotypic and phenotypic data sets will be combined in a Genome-Wide Association Scan (GWAS) to identify wild barley alleles that improve plant performance under stress. Because the gene resolution is extremely high this study will yield individual high confidence candidate alleles that putatively regulate the studied traits.Fifth, to validate the identified trait-improving exotic alleles in follow up studies, high-resolution offspring populations derived from the originally studied HEB-25 lines will be developed in Halle by backcrossing.The expected outcome of the BARLEY-NAM project will be beneficial in two directions. On one hand, the molecular regulation of new HEB properties will be studied in detail using the developed backcross lines. On the other hand, trait improving exotic alleles will be used in future breeding programs. This will ultimately lead to new elite barley cultivars with improved properties and, simultaneously, extend the biodiversity of our modern elite barley gene pool due to the incorporation of wild barley germplasm.