Assessing wild barley germplasm in multiparent and advanced backcross populations for mapping, gene discovery, and improvement of malting barley

Abstract

Wild barley (Hordeum vulgare ssp. spontaneum), the progenitor of cultivated barley (Hordeum vulgare ssp. vulgare), is a rich source of genetic diversity. This diversity is not easily exploited due to challenges inherent in identifying and extracting beneficial alleles from widely unadapted germplasm. Wild barley germplasm has been shown to contain valuable alleles for several disease resistance and abiotic stress tolerance traits, and due to its extensive diversity, it is a key target for expanding the limited diversity of cultivated breeding germplasm. Therefore, our aim was to create and characterize populations that incorporate diverse sources of wild barley germplasm into cultivated barley backgrounds using advanced backcross (AB) and nested association mapping (NAM) techniques. To do this, we created a wild barley AB-NAM population by backcrossing 25 wild barley accessions to the 6-rowed malting barley cultivar Rasmusson. The 25 wild barley parents were selected to capture approximately ~90% of the allelic content of the wild barley diversity collection (WBDC), which contains 318 accessions sourced from across wild barley’s native range. The resulting set of 796 BC2F4:6 lines were genetically characterized and analyzed in augmented field trials for agronomic, yield, grain protein, and wax production traits. Additionally, we analyzed the Harrington (2-rowed malting barley cultivar) x OUH-602 (wild barley accession), biparental AB population for yield and malting quality characteristics. The AB-NAM population was genotyped with 384 SNP markers and 263,531 markers were imputed onto the population from exome capture sequence of the parents. Linkage disequlibrium in the AB-NAM was significantly lower than the HOUH biparental mapping population, indicating a higher potential mapping resolution. Qualitative traits were mapped to candidate gene resolution and beneficial alleles were identified for several quantitative traits. Ultimately, the AB-NAM population will serve as a community resource for barley breeders and geneticists to explore a large proportion of wild barley germplasm in a single, relatively adapted mapping population.