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.地方品种作物（landrace crops）由本地适应、遗传漂变（genetic drift）以及通过种子交流实现的基因流（gene flow）塑造而成。反之，对地方品种种群间遗传结构的研究，可以揭示这些演化力量随时间推移产生的影响。本研究针对40个瑞典豌豆（*Pisum sativum* L.）种群开展遗传多样性分析，这些种群的样本既有19世纪晚期的历史种子样品，也有20世纪晚期收集的现存基因库种质（gene bank accessions）。历史样品的群体内遗传多样性始终维持在较高水平，而现存种质的群体内遗传多样性水平则参差不齐，且整体低于历史样品。结构分析与主成分分析（principal component analysis）结果显示，绝大多数现存与历史种质均可按地理起源聚为不同类群。按县域开展的种质分析表明，历史种质的遗传多样性分布高度重叠。与之相反，多数现存种质均表现出遗传漂变的特征：它们仅保留了历史种质中的部分等位基因（allele），且种群间的遗传分化程度更高。本研究结果揭示了20世纪期间历史存在的集合种群（metapopulations）是如何得以保留的——尽管这些种群如今已演变为遗传上相互隔离的类群。