Population structure and migration of the Tobacco Blue Mold Pathogen, Peronospora tabacina, into North America and Europe.

Neutrality tests were significant and the equilibrium model of neutral evolution was rejected, indicating an excess of recent mutations or rare alleles. Hudson's Snn tests were performed to examine population subdivision and gene flow among populations. An isolation-with-migration analysis (IM) supported the hypothesis of long-distance migration of P. tabacina from the Caribbean region, Florida and Texas into other states in the United States. Within the European populations, the model documented migration from North Central Europe into western Europe and Lebanon, and migration from western Europe into Lebanon. The migration patterns observed support historical observations about the first disease introductions and movement in Europe. The models developed are applicable to other aerial dispersed emerging pathogens and document that high-evolutionary-risk plant pathogens can move over long distances to cause disease due to their large effective population size, population expansion and dispersal.