Barley Domestication, Adaptation and Population Genomics

Abstract

Wild and cultivated barley are characterized by a high level of genetic diversity and a pronounced geographic population structure. Numerous studies using a diversity of markers showed that the centre of diversity of both wild and cultivated barley is in the Western part of the Fertile Crescent where the species was presumably domesticated. Comparisons of geographic diversity patterns suggested additional centres of domestication, of which the Eastern part of the Fertile Crescent (Iran or Himalaya), are most strongly supported. In wild barley, the geographic distribution of genetic and phenotypic diversity largely follows a neutral isolation by distance pattern, but common-garden experiments and environmental association studies indicate that local adaptation by natural selection also had a significant influence on these patterns but, so far no strong candidate genes for local adaptation were identified. Cultivated barley landraces and elite material have a significantly reduced level of genetic diversity compared to wild barley which also shows significant geographic differentiation and evidence for local adaptation. Several major domestication genes have already been cloned and patterns of diversity largely confirm the hypotheses that these genes were exposed to strong domestication-related selection that caused a reduction of diversity in these genes. Ex situ genebank collections of wild and domesticated barley were used to define core collections that have been phenotyped and genotyped to facilitate allele mining and introgression into elite varieties. The future utilization of barley genetic diversity will be facilitated by a good reference genome. The rapid progress of sequencing technologies and modern breeding methods like genomic selection and genome editing will contribute to an efficient utilization of barley genetic diversity.