Nineteenth century seeds reveal the population genetics of landrace barley (Hordeum vulgare).

Barley (Hordeum vulgare) is a major crop, grown worldwide and in a wide range of climatic conditions. Despite its importance as a crop species, little is known about the population genetics of barley and the effects of bottlenecks, adaptation, and gene flow on genetic diversity within and between landrace populations. In areas with highly developed agriculture, such as Northern Europe, these types of genetic studies are hampered by lack of landraces preserved in situ or ex situ. Here, we report a genetic study of Swedish landrace barley using 113-year-old seed samples. The results demonstrate differing levels of variation with some latitudinal effect. We also detect clear population differentiation and population structure within Sweden into a southern and a northern cluster. These results possibly reflect different introduction routes of barley into Sweden. We thus show that the study of historic material can be an important alternative for regions where no or little extant landrace material is available.