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.
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