|Grunwald, Niklaus - Nik|
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2011
Publication Date: 9/16/2011
Citation: Goss, E.M., Cardenas, M.E., Myers, K., Forbes, G.A., Fry, W.E., Restrepo, S.O., Grunwald, N.J. 2011. The plant pathogen Phytophthora andina emerged via hybridization of an unknown Phytophthora species and the Irish famine pathogen, P. infestans. PLoS One. 6(9):e24543. doi: 10.1371/journal.pone.0024543. Interpretive Summary: Emerging plant pathogens have caused ecological destruction and economic losses. Most of these pathogens have emerged as a result of being moved around the globe in trade and introduced to new regions where hosts may have little or no resistance to these pathogens. New fungal pathogens have also been formed from sexual or parasexual reproduction between two previously distinct species. Here we show that Phytophthora andina, which is a pathogen of Andean Solanum crops, is a hybrid pathogen. Phytophthora andina is of particular interest because one of its parents is the pathogen associated with the Irish potato famine, the potato late blight pathogen P. infestans that is infamous for its global movement. Notably, P. andina does not infect potato or tomato, the hosts of P. infestans. The other parent of P. andina is an unknown species that is closely related to P. infestans, but has not been collected to date.
Technical Abstract: The global movement of plant pathogens threatens natural ecosystems, food security, and commercial interests. Introduction of a plant pathogen to new geographic regions has been the primary mechanism by which new pathogens have emerged. Another documented mechanism for the emergence of plant pathogens is hybridization between individuals of different species or subspecies. Hybridization may allow rapid evolution and adaptation to new hosts or environments. Hybrid plant pathogens have traditionally been difficult to detect or confirm, but the increasing ease of cloning and sequencing PCR products now makes the identification of species that consistently have genes or alleles with phylogenetically divergent origins relatively straightforward. We investigated the genetic origin of Phytophthora andina, an increasingly common pathogen of Andean crops Solanum betaceum, S. muricatum, S. quitoense, and several wild Solanum spp. in Colombia, Peru, and Ecuador. We cloned four nuclear loci to obtain haplotypes and used these loci to infer the phylogenetic relationships of P. andina to the potato late blight pathogen P. infestans and other related species. Sequencing of cloned PCR products in every case revealed two distinct haplotypes for each locus in P. andina, such that each isolate had one allele derived from a P. infestans parent and a second divergent allele derived from an unknown species that is closely related but distinct from P. infestans, P. mirabilis, and P. ipomoeae. To the best of our knowledge, the unknown parent has not yet been collected. We also observed sequence polymorphism among P. andina isolates at three of the four loci, many of which segregate between previously described P. andina clonal lineages. These results provide strong support that P. andina emerged via hybridization between P. infestans and another unknown Phytophthora species also belonging to Phytophthora clade 1c.