Data from: Farmers without borders - genetic structuring in century old barley (Hordeum vulgare)

The geographic distribution of genetic diversity can reveal the evolutionary history of a species. For crop plants, phylogeographic patterns also indicate how seed has been exchanged and spread in agrarian communities. Such patterns are, however, easily blurred by the intense seed trade, plant improvement and even genebank conservation during the twentieth century, and discerning fine-scale phylogeographic patterns is thus particularly challenging. Using historical crop specimens, these problems are circumvented and we show here how high-throughput genotyping of historical nineteenth century crop specimens can reveal detailed geographic population structure. Thirty-one historical and nine extant accessions of North European landrace barley (Hordeum vulgare L.), in total 231 individuals, were genotyped on a 384 single nucleotide polymorphism assay. The historical material shows constant high levels of within-accession diversity, whereas the extant accessions show more varying levels of diversity and a higher degree of total genotype sharing. Structure, discriminant analysis of principal components and principal component analysis cluster the accessions in latitudinal groups across country borders in Finland, Norway and Sweden. FST statistics indicate strong differentiation between accessions from southern Fennoscandia and accessions from central or northern Fennoscandia, and less differentiation between central and northern accessions. These findings are discussed in the context of contrasting historical records on intense within-country south to north seed movement. Our results suggest that although seeds were traded long distances, long-term cultivation has instead been of locally available, possibly better adapted, genotypes.

遗传多样性的地理分布能够揭示物种的演化历史。对于作物而言，系统地理学（phylogeography）格局还可反映种子在农业社群中的交流与传播路径。然而，20世纪以来高强度的种子贸易、作物改良乃至种质资源库（genebank）保藏工作极易模糊这类格局，因此精细尺度的系统地理学格局识别极具挑战性。
利用历史作物标本可规避上述问题，本研究证实，对19世纪历史作物标本开展高通量基因分型（high-throughput genotyping），能够揭示精细的地理种群结构。本研究对北欧地方栽培大麦（Hordeum vulgare L.）的31份历史标本与9份现存供试种质共231个个体，采用384位点单核苷酸多态性（single nucleotide polymorphism, SNP）分型检测体系进行基因分型。
历史标本材料展现出稳定的高群体内多样性水平，而现存供试种质的多样性水平波动更大，且整体基因型共享比例更高。群体结构分析软件（Structure）、主成分判别分析（discriminant analysis of principal components, DAPC）与主成分分析（principal component analysis, PCA）均将供试种质按纬度群组聚类，且该聚类结果跨越芬兰、挪威与瑞典的国境边界。
FST统计量显示，南芬诺斯堪的亚地区的供试种质与中、北芬诺斯堪的亚地区的供试种质之间存在显著遗传分化，而中、北地区的供试种质间分化程度较低。
本研究结合关于国内南北种子高强度流动的相悖历史记录，对上述发现展开了讨论。研究结果表明，尽管种子曾进行长距离贸易，但长期栽培中占据主导的实则为当地适应性更强的基因型。