Mapping Agronomic Traits in a Wild Barley Advanced Backcross-Nested Association Mapping Population

Crop improvement relies on the ability to utilize novel genetic variation. Six-rowed malting barley (Hordeum vulgare L. subsp. vulgare) developed in the US Midwest has an especially narrow genetic base. Therefore, developing strategies to widen the genetic base in barley is important for continued crop improvement. A wild barley [Hordeum vulgare L. subsp. spontaneum (K. Koch) Thell.] advanced backcross-nested association mapping (AB-NAM) population was developed to assess wild-barley-derived alleles in an elite spring six-rowed malting barley background. The 796 BC2F4:6 lines in the AB-NAM were derived from 25 wild barley accessions backcrossed to the cultivar Rasmusson. Because the AB-NAM design minimizes the deleterious and unadapted traits of the wild barley parents, the population was screened in five field environments for the agronomic traits: days to heading, height, productive tiller number (PTN), test weight, and yield. The number of loci identified ranged from two (PTN, the trait with the lowest heritability) to 19 (height). Domestication-related genes were identified for each trait, particularly the photoperiod gene Ppd-H1 for days to heading, height, and PTN and the nonbrittle Btr1/Btr2 loci for test weight and yield. Only a single variant showed beneficial variation for yield from a wild barley allele, but positive effects were identified for the other traits examined, including positive variants for test weight on chromosomes 1H and 3H. The AB-NAM population is a novel resource to map agronomically important traits associated with wild barley alleles.