Abstract
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.
Highlights
Global trade has dramatically increased the chances of pathogens to be spread artificially around the world, on or with traded goods [1,2,3]
Previous studies have indicated that selfing reduces genetic diversity and effective population size and considerably increases the level of homozygosity relative to sexual populations [71,72,73]
High degrees of homozygosity were previously observed in P. alni subsp. uniformis [74] and in P. sojae [75], which are, to our knowledge, the only other homothallic Phytophthora species that have been investigated so far using population genetic tools
Summary
Global trade has dramatically increased the chances of pathogens to be spread artificially around the world, on or with traded goods [1,2,3]. The introduction of a pathogenic organism into a new area may result in a biological invasion with devastating ecological and economic consequences [3,4]. Recent invasive diseases with dramatic consequences have gained a lot of attention, e.g. the worldwide amphibian dieback caused by the chytrid fungus Batrachochytrium dendrobatidis, where global trading of African clawed frogs (Xenopus laevis) for laboratory purposes resulted in dispersal of the pathogen [7]. Other well known invasive fungal diseases include those affecting major food crops, such as the rice blast disease (Magnaporthe oryzae, Ascomycota) which cause severe losses of harvests of wheat and barley [8] or the downy mildews of grapevines (Plasmopara viticola) and hop (Pseudoperonospora humili) [9,10]
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