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 requires a revolution in breeding crops that deliver high and sustainable yield under fluctuating disadvantageous environmental conditions. The ancestral wild germplasm of modern crops contains allelic variants that can achieve this goal, yet modern crops are becoming increasingly depleted in biodiversity. The two key obstacles to successful exploitation of wild germplasm are finding the wild-derived alleles needed and testing them in the field.The BARLEY-NAM project will use wild barley (Hordeum vulgare ssp. spontaneum) as a model and apply novel genomic and breeding tools to improve agronomic performance of elite barley under abiotic and biotic stresses. For this, we will apply the nested association mapping (NAM) approach using the first cereal NAM population, HEB-25. HEB-25 comprises 1,420 BC1S3 lines, sub-divided into 25 families, originating from crosses of the elite barley cultivar Barke with 25 different wild barley donors. The HEB-25 lines will first be assessed for allele content at 21,643 genes (every known high-confidence barley gene), employing state-of-the-art exome capture and next generation sequencing. We expect to map roughly 400,000 SNPs within HEB-25 giving unprecedented levels of gene and genome resolution for barley. Second, all HEB lines will be cultivated in field trials in Germany, Scotland and Israel to assess agronomic performance under nitrogen deficiency, drought and pathogen attack. Yield components and nutrient content will be scored, as well as resistance against the major barley diseases leaf rust, yellow rust and net blotch. In addition, agronomic performance will be modelled by non-invasive remote sensing technology to establish phenotype predictions. Third, the collected data sets will be archived and further processed in a central data warehouse, built around a custom web-accessible relational database. Fourth, genotype and phenotype data of HEB-25 will be combined in a genome-wide association scan (GWAS) to identify wild barley alleles that improve plant performance under stress. Since the gene resolution is extremely high, this study will yield individual high confidence candidate genes that putatively regulate the studied traits. Fifth, to validate the identified trait-improving exotic alleles, segregating high-resolution progeny will be developed from the HEB lines. The BARLEY-NAM project will be beneficial in two directions. On the one hand, the genes and gene variants regulating agronomic traits in barley will be defined at a level of detail unprecedented for the crop and this will inform future strategies for parallel improvement in wheat and rye. On the other hand, trait-improving wild barley alleles will be available for application in future barley breeding. This will lead to new barley cultivars with improved performance and extend the biodiversity and sustainability of the elite barley gene pool.