Data from: Population genetic analysis of a parasitic mycovirus to infer the invasion history of its fungal host

Hymenoscyphus fraxineus mitovirus 1 (HfMV1) occurs in the fungus Hymenoscyphus fraxineus, an introduced plant pathogen responsible for the devastating ash dieback epidemic in Europe. Here, we explored the prevalence and genetic structure of HfMV1 in order to elucidate the invasion history of both the virus and the fungal host. A total of 1298 H. fraxineus isolates (181 from Japan and 1117 from Europe) were screened for the presence of this RNA virus and 301 virus-positive isolates subjected to partial sequence analysis of the viral RNA polymerase gene. Our results indicate a high mean prevalence (78.7%) of HfMV1 across European H. fraxineus isolates, which is supported by the observed high transmission rate (average 83.8%) of the mitovirus into sexual spores of its host. In accordance with an expected founder effect in the introduced population in Europe, only 1.1% of the Japanese isolates were tested virus positive. In Europe, HfMV1 shows low nucleotide diversity but a high number of haplotypes, which seem to be subjected to strong purifying selection. Phylogenetic and clustering analysis detected two genetically distinct HfMV1 groups, both present throughout Europe. This pattern supports the hypothesis that only two (mitovirus-carrying) H. fraxineus individuals were introduced into Europe as previously suggested from the bi-allelic nature of the fungus. Moreover, our data points to reciprocal mating events between the two introduced individuals, which presumably initiated the ash dieback epidemic in Europe.白蜡树枯梢病菌线粒体病毒1号（Hymenoscyphus fraxineus mitovirus 1, HfMV1）寄生于白蜡树枯梢病菌（Hymenoscyphus fraxineus）中，该真菌作为外来植物病原物，引发了欧洲破坏性极强的白蜡枯梢病疫情。本研究针对HfMV1的流行率与遗传结构展开探究，以期阐明该病毒及其真菌宿主的入侵历史。本研究共对1298株白蜡树枯梢病菌分离株（其中181株采自日本，1117株采自欧洲）开展该RNA病毒的检测筛选，并对301株病毒阳性分离株的病毒RNA聚合酶基因进行部分序列分析。研究结果显示，欧洲地区的白蜡树枯梢病菌分离株中，HfMV1的平均流行率高达78.7%；这一结果得到了该线粒体病毒向宿主有性孢子的高传播率（平均83.8%）的佐证。与欧洲引入种群中预期的奠基者效应相符，日本分离株的病毒阳性率仅为1.1%。在欧洲地区，HfMV1的核苷酸多样性较低，但单倍型数量较多，且似乎受到强烈的纯化选择作用。系统发育与聚类分析发现了两个遗传特征显著不同的HfMV1类群，且二者在欧洲全境均有分布。该分布模式佐证了此前基于该真菌的双等位基因特性提出的假说：仅有两株携带线粒体病毒的白蜡树枯梢病菌个体被引入欧洲。此外，本研究的数据表明这两个引入个体之间存在双向交配事件，推测这一过程正是欧洲白蜡枯梢病疫情的起源。