Modern agricultural practices and the climate change foster the rapid spread of plant pathogens like the maize fungal pathogen Setosphaeria turcica, which causes Northern corn leaf blight and expanded into Central Europe since the 1980s. To investigate the rapid expansion of S. turcica we sequenced 121 isolates from Europe and Kenya. Population genomic inference revealed a single genetically diverse cluster in Kenya and three clonal lineages with low diversity and one cluster of multiple clonal sublineages in Europe. Phylogenetic dating suggests that all European lineages originated by sexual reproduction outside Europe and subsequently were subsequently introgressed multiple times. In contrast to Kenyan isolates, European isolates did not show sexual recombination despite the presence of both MAT1-1 and MAT1-2 mating types. Coalescent analysis of the geographically most widespread European lineage supported a neutral, strongly exponential population growth model over models with natural selection caused by host defence resistance or environmental adaptation. Within clonal lineages, we observed phenotypic variation in virulence to different monogenic resistances that may originate from repeated mutations in virulence genes. Association mapping between genetic clusters did not identify genomic regions associated with pathogen races but uncovered strongly differentiated genomic regions between clonal lineages that harbor putative effector genes. In conclusion, the expansion and population growth of S. turcica in Europe was mainly driven by the expansion of maize cultivation area and not by rapid adaptation.

中文翻译：

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玉米真菌病原体在欧洲反复引入并迅速扩展的种群基因组证据

现代农业实践和气候变化促进了植物病原体的快速传播，如玉米真菌病原菌Setosphaeria turcica，这种植物病原体导致北部玉米叶枯萎病，并自1980年代以来扩展到中欧。调查S. turcica的快速膨胀我们对来自欧洲和肯尼亚的121个分离株进行了测序。人口基因组推断揭示了肯尼亚的一个单一遗传多样性集群和三个低多样性的克隆谱系以及欧洲多个克隆亚谱系的集群。系统发生约会表明，所有欧洲血统都起源于欧洲以外的有性生殖，随后又多次渗入。与肯尼亚分离株相反，尽管存在MAT1-1和MAT1-2，欧洲分离株也未表现出性重组交配类型。对地理分布最广的欧洲血统的联合分析支持了中性，强指数的人口增长模型，而不是由宿主防御或环境适应导致的自然选择模型。在克隆谱系中，我们观察到了针对不同单基因抗性的毒力表型变异，这可能源于毒力基因的重复突变。遗传簇之间的关联作图无法识别与病原体种族相关的基因组区域，但未发现带有推定效应子基因的克隆谱系之间的强分化基因组区域。总之，欧洲S. turcica的扩张和种群增长主要是由玉米种植面积的扩大而不是快速适应引起的。