Peronospora odessana sp. nov., a downy mildew pathogen of a Tertiary relict species, Gymnospermium odessanum.
A new species of Peronospora is described from Gymnospermium odessanum, a rare spring geophyte considered a Tertiary relict in the northwestern Black Sea region of Ukraine, Moldova and Romania. Phylogenetic analyses based on a combined matrix of the internal transcribed spacer-large subunit (ITS-LSU) ribosomal DNA (rDNA) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) and cox2 genes demonstrate that it is a clearly distinct undescribed species. Morphological descriptions and illustrations of its oospores, conidiophores and conidia are provided. Despite its distinctive disease symptoms, the species has remained undetected until now, probably due to the rarity of its host. Peronospora odessana is the second species from Berberidaceae and is morphologically clearly distinct from P. achlydis on Achlys japonica. The closest relatives of P. odessana were not revealed, but it is closely related to Peronospora bulbocapni, P. dicentrae and P. chrysosplenii, the hosts of which are also spring geophytes. Sequence data confirm that cox1 and cox2 are good barcoding loci; they show a similar number of nucleotide differences to its closest relatives.