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Title: Defining species boundaries in the genus Phytophthora: the case of Phytophthora andina. A response to “Phytophthora andina sp. nov., a newly identified heterothallic pathogen of solanaceous hosts in the Andean highlands

Author
item CARDENAS, M - University Of Los Andes
item TABIMA, J - University Of Los Andes
item FRY, W - Cornell University
item Grunwald, Niklaus - Nik
item BERNAL, A - University Of Los Andes
item RESTREPO, S - University Of Los Andes

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2011
Publication Date: 4/2/2012
Citation: Cardenas, M.E., Tabima, J., Fry, W.E., Grunwald, N.J., Bernal, A.J., Restrepo, S.O. 2012. Defining species boundaries in the genus Phytophthora: the case of Phytophthora andina. A response to “Phytophthora andina sp. nov., a newly identified heterothallic pathogen of solanaceous hosts in the Andean highlands." Plant Pathology. 61(2):215-220.

Interpretive Summary: The newly described species Phytophthora andina is a relative of the potato late blight pathogen P. infestans. In this letter to the editor we argue that the formal species description is incomplete because the phylogenetic analysis classifies P. andina into two separate species. Clearly, P. andina needs to be grouped into one phylogenetic species to be acceptable. We argue that hybridization might be responsible for the results observed.

Technical Abstract: The newly described species Phytophthora andina is a relative of the potato late blight pathogen P. infestans. The formal P. andina species description is based on three types of evidence. First, the fact that these Ecuadorian isolates were found causing disease on different wild Solanum spp. that are non hosts for P. infestans. Second, an AFLP analysis clearly separated both species into different clades by means of neighbor joining. Third, phylogenetic analysis that, as we argue here, was less compelling than the fist two lines of evidence mentioned above. We believe that the CoxII phylogeny presented in the species description does not support P. andina as a monophyletic species. In fact, P. andina is placed into two separate clades with significant bootstrap support. As a result, we argue that the species description for P. andina is incomplete and more sequence-based work is required to conclusively name P. andina a novel taxon. The phylogenetic species concept requires a monophyletic grouping and the congruence among different gene genealogies to avoid inferring conclusions from a gene tree instead of a species tree. Furthermore, a novel Phytophthora species description should ideally be based on more than one sequenced locus and should include both the mitochondrial and nuclear genomes. Including nuclear genes is important because recombination events subsequent to speciation can only be detected in nuclear data as mitochondrial regions are maternally inherited. While we believe that P. andina is a new species, our analysis shows that further work is needed to understand the evolutionary history of P. andina. One mechanism that could explain the distinct nature of P. andina could be hybridization.