Pathogen introductions have led to numerous disease outbreaks in naive regions of the globe. The plant pathogen Xylella fastidiosa has been associated with various recent epidemics in Europe affecting agricultural crops, such as almond, grapevine, and olive, but also endemic species occurring in natural forest landscapes and ornamental plants. We compared whole-genome sequences of X. fastidiosa subspecies multiplex from America and strains associated with recent outbreaks in southern Europe to infer their likely origins and paths of introduction within and between the two continents. Phylogenetic analyses indicated multiple introductions of X. fastidiosa subspecies multiplex into Italy, Spain, and France, most of which emerged from a clade with limited genetic diversity with a likely origin in California, USA. The limited genetic diversity observed in X. fastidiosa subspecies multiplex strains originating from California is likely due to the clade itself being an introduction from X. fastidiosa subspecies multiplex populations in the southeastern United States, where this subspecies is most likely endemic. Despite the genetic diversity found in some areas in Europe, there was no clear evidence of recombination occurring among introduced X. fastidiosa strains in Europe. Sequence type taxonomy, based on multilocus sequence typing (MLST), was shown, at least in one case, to not lead to monophyletic clades of this pathogen; whole-genome sequence data were more informative in resolving the history of introductions than MLST data. Although additional data are necessary to carefully tease out the paths of these recent dispersal events, our results indicate that whole-genome sequence data should be considered when developing management strategies for X. fastidiosa outbreaks.

IMPORTANCE Xylella fastidiosa is an economically important plant-pathogenic bacterium that has emerged as a pathogen of global importance associated with a devastating epidemic in olive trees in Italy associated with X. fastidiosa subspecies pauca and other outbreaks in Europe, such as X. fastidiosa subspecies fastidiosa and X. fastidiosa subspecies multiplex in Spain and X. fastidiosa subspecies multiplex in France. We present evidence of multiple introductions of X. fastidiosa subspecies multiplex, likely from the United States, into Spain, Italy, and France. These introductions illustrate the risks associated with the commercial trade of plant material at global scales and the need to develop effective policy to limit the likelihood of pathogen pollution into naive regions. Our study demonstrates the need to utilize whole-genome sequence data to study X. fastidiosa introductions at outbreak stages, since a limited number of genetic markers does not provide sufficient phylogenetic resolution to determine dispersal paths or relationships among strains that are of biological and quarantine relevance.

病原体的引入导致了全球幼稚地区的许多疾病暴发。植物病原体Xylella fastidiosa与欧洲最近的各种流行病有关，这些流行病影响农作物，例如杏仁，葡萄和橄榄，但也存在于自然森林景观和观赏植物中的特有物种。我们比较了来自美国的多头X. fastidiosa亚种的全基因组序列，以及与南欧近期暴发相关的菌株，以推断它们可能的起源和在两大洲之间和之间的引入途径。系统发育分析表明，X. fastidiosa亚种多重引入。进入意大利，西班牙和法国，其中大多数来自进化枝，遗传多样性有限，可能起源于美国加利福尼亚。在起源于加利福尼亚州的fastidiosa亚种多重菌株中观察到的有限的遗传多样性可能是由于进化枝本身是来自美国东南部的fast.osa亚种多重种群的引入，而该亚种最可能是地方性的。尽管在欧洲某些地区发现了遗传多样性，但没有明确的证据表明引进的X. fastidiosa之间发生重组。欧洲菌株。结果表明，至少在一种情况下，基于多基因座序列类型（MLST）的序列类型分类法不会导致这种病原体的单系进化。与MLST数据相比，全基因组序列数据在解析引种历史方面提供了更多信息。尽管需要额外的数据来仔细弄清这些最近的传播事件的发生路径，但我们的结果表明，在制定针对食指假单胞菌暴发的管理策略时，应考虑全基因组序列数据。

重要性 叶缘焦枯病菌是一种重要的经济植物致病菌已成为与橄榄树在意大利相关的毁灭性流行病相关的全球性的重要病原体X. fastidiosa亚种pauca等欧洲爆发，如X. fastidiosa亚种fastidiosa和X. fastidiosa亚种复在西班牙和X. fastidiosa亚种复在法国。我们提供了X. fastidiosa亚种多重引入的多种证据。，可能来自美国，进入西班牙，意大利和法国。这些介绍说明了在全球范围内与植物材料的商业贸易有关的风险，以及需要制定有效的政策以限制病原体污染到幼稚地区的可能性。我们的研究表明，需要利用全基因组序列数据来研究暴发性疟原虫的传入，因为数量有限的遗传标记不能提供足够的系统发育分辨率来确定与生物和检疫相关的菌株之间的传播途径或相关性。 。