The origin of Phytophthora infestans populations present in Europe in the 1840s: A critical review of historical and scientific evidence

A critical review of available historical and scientific evidence related to the question of the origin of the first European populations of the potato late blight pathogen Phytophthora infestans is presented. It shows that the bases for the current theories of a direct introduction of the fungus into Europe and North America from either a Mexican or an Andean centre of origin and of diversity are questionable. An alternative theory, involving a three-step process: (i) migration from central Mexico to South America several centuries ago; (ii) migration from South America to the US in 1841-1842, and (iii) migration to Europe from either South America, US or both in 1843-1844, is in good agreement with both the historical records and with the genetics and structure of current populations.