Schematic representation of the time-line for the emergence of major lineages of Phytophthora infestans, the pathogen that causes late blight in potatoes, as proposed by Burbano and co-workers (Yoshida et al., 2013). P. infestans and P. mirabilis (a pathogen that does not infect potatoes) are thought to have diverged from a common ancestor about 1200 years ago. Since then there have been at least three major migrations of P. infestans from a sexually reproducing population in Mexico (shown by black triangles). The first involves a metapopulation established in an unknown region, from which HERB-1 and US-1 emerged and spread around the world. US-1 is rarely found in contemporary populations (as indicated by the dotted black line) and HERB-1 is not found anywhere today (red cross). A shipment of potatoes from Mexico into Europe during a drought in 1976 is thought to be the source of the population of P. infestans that displaced US-1 in Europe and resulted in the emergence of aggressive new clones such as 13_A2 (also known as Blue13). Lastly, independent migrations into the US resulted in the dominance of the US-8 lineage, although this is now being displaced by other lineages such as US-22. The precise timing of the displacement of HERB-1 by US-1 remains undefined.