Population History and Pathways of Spread of the Plant Pathogen Phytophthora plurivora

Human activity has been shown to considerably affect the spread of dangerous pests and pathogens worldwide. Therefore, strict regulations of international trade exist for particularly harmful pathogenic organisms. Phytophthora plurivora, which is not subject to regulations, is a plant pathogen frequently found on a broad range of host species, both in natural and artificial environments. It is supposed to be native to Europe while resident populations are also present in the US. We characterized a hierarchical sample of isolates from Europe and the US and conducted coalescent-, migration, and population genetic analysis of sequence and microsatellite data, to determine the pathways of spread and the demographic history of this pathogen. We found P. plurivora populations to be moderately diverse but not geographically structured. High levels of gene flow were observed within Europe and unidirectional from Europe to the US. Coalescent analyses revealed a signal of a recent expansion of the global P. plurivora population. Our study shows that P. plurivora has most likely been spread around the world by nursery trade of diseased plant material. In particular, P. plurivora was introduced into the US from Europe. International trade has allowed the pathogen to colonize new environments and/or hosts, resulting in population growth.已有研究表明，人类活动会在全球范围内显著影响危险性有害生物与植物病原物的传播扩散。为此，针对危害性极强的病原生物，各国已制定严格的国际贸易监管规范。多主疫霉（Phytophthora plurivora）暂未被纳入监管范畴，是一种植物病原物，常于自然与人工环境中侵染多种宿主植物。学界普遍认为其原生分布区域为欧洲，但美国亦存在定殖种群。本研究对采自欧洲与美国的分层抽样分离株样本开展特征鉴定，并针对序列数据与微卫星（microsatellite）标记数据进行溯祖分析、迁移分析及群体遗传学分析，以明确该病原物的传播路径与种群历史动态。研究发现，多主疫霉的种群遗传多样性处于中等水平，但未呈现地理分化结构；欧洲内部存在高水平的基因交流，且存在由欧洲向美国的单向基因流动。溯祖分析结果显示，全球多主疫霉种群近期存在扩张信号。本研究证实，多主疫霉极有可能通过带病害植物材料的苗木贸易实现全球传播，其中美国的多主疫霉种群系由欧洲引入。国际贸易助力该病原物侵染全新环境与/或宿主，进而推动其种群规模扩张。