|Evolutionary relationships and displacements of historic and present day Phytophthora infestans|
A. Saville (1), M. D. Martin (2), M. T. Gilbert (2), J. B. RISTAINO (1). (1) North Carolina State University, Raleigh, NC, U.S.A.; (2) Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen,, Copenhagen K, Denmark., Denmark
<i>Phytophthora infestans </i>caused the historic potato famine and is an important constraint to potato production worldwide. The evolutionary relationships of modern clonal lineages of the pathogen and historic <i>P. infestans</i> in herbarium samples from old and new world collections were examined using nuclear and mitochondrial genomes and multilocus genealogies. Multiple distinct genotypes were present in historical Europe and a suite of infection-related genes were different from modern strains. Historic outbreaks were not caused by the US-1 clonal lineage (1b mtDNA haplotype) but by a closely related sister lineage of the Ia mtDNA haplotypes, Herb-1, that was found in modern New World populations from both Mexico and South America. The US-1 lineage formed a distinct cluster from most modern US lineages in PCA and STRUCTURE analysis of RFLP fingerprints. A maximum-likelihood phylogeny, coalescent analyses, and population subdivision statistics for the RXLR effectors <i>PiAVR2 </i>and <i>PiAVR2-like </i>showed four haplotypes that diverged into two lineages. <i>PiAVR2</i> but not <i>PiAVR2-like</i> haplotypes were present in historic samples screened thus far. Six haplotypes were observed for IRRAS, and early 20th-century <i>P. infestans</i> shared haplotypes with modern lineages, while other haplotypes from 19th century outbreaks were distinct. Our data suggest multiple global introductions of <i>P. infestans</i> and the displacement of these lineages over time.