Data from: Twentieth-century changes in the genetic composition of Swedish field pea metapopulations

Landrace crops are formed by local adaptation, genetic drift and gene flow
through seed exchange. In reverse, the study of genetic structure between
landrace populations can reveal the effects of these forces over time. We
present here the analysis of genetic diversity in 40 Swedish field pea
(Pisum sativum L.) populations, either available as historical seed
samples from the late nineteenth century or as extant gene bank accessions
assembled in the late twentieth century. The historical material shows
constant high levels of within-population diversity, whereas the extant
accessions show varying, and overall lower, levels of within-population
diversity. Structure and principal component analysis cluster most
accessions, both extant and historical, in groups after geographical
origin. County-wise analyses of the accessions show that the genetic
diversity of the historical accessions is largely overlapping. In
contrast, most extant accessions show signs of genetic drift. They harbor
a subset of the alleles found in the historical accessions and are more
differentiated from each other. These results reflect how, historically
present metapopulations have been preserved during the twentieth century,
although as genetically isolated populations.