Re-evaluation of the Phytophthora cryptogea species complex and the description of a new species, Phytophthora pseudocryptogea sp. nov

Abstract

Many studies over recent years have recognised Phytophthora cryptogea as a species complex, with several distinct lineages perhaps representing as yet undescribed species. Additionally, the taxonomic status of the related species P. erythroseptica is also a matter of controversy. In this study, phylogenetic relationships were clarified using nuclear (internal transcribed spacers, s-tubulin, heat shock protein 90, elicitin) and mitochondrial (cytochrome c oxidase subunit I, NADH dehydrogenase subunit I) gene regions. Our results showed three distinct phylogenetic lineages within P. cryptogea in combined nuclear and mitochondrial gene trees. The molecular divergence observed among these three phylogenetic lineages justifies their re-description as separate species. The first group, including the type isolate, is P. cryptogea sensu stricto, the second group corresponds to the undescribed taxon P. sp. kelmania and the third group is described here as P. pseudocryptogea sp. nov. Although some morphological differences between P. cryptogea and P. pseudocryptogea were notable, they were not sufficient to reliably distinguish these species. Moreover, in all of our phylogenetic trees (with the exception of elicitin), P. erythroseptica isolates were in a strongly supported monophyletic clade. This clade shares a recent common ancestor with P. cryptogea sensu stricto, but is clearly distinct from P. cryptogea. Our results therefore confirmed the position of P. erythroseptica as a distinct species and a close relative to the P. cryptogea species complex.