Phytophthora gemini sp. nov., a new species isolated from the halophilic plant Zostera marina in the Netherlands

Eight strains belonging to the Oomycete genus Phytophthora were isolated from Zostera marina (seagrass) in The Netherlands over the past 25 y. Based on morphology, isozymes, temperature–growth relationships and ITS sequences, these strains were found to belong to two different Phytophthora species. Five strains, four of them isolated from rotting seeds and one isolated from decaying plants, could not be assigned to a known species and hence belong to a new species for which we propose the name Phytophthora gemini sp. nov. Three strains were isolated from decaying plants and were identified as Phytophthora inundata, thereby expanding the known habitat range of this species from fresh to brackish-saline areas. The possible role of both Phytophthora species in the decline of Z. marina in The Netherlands and the evolutionary significance of the presence of Phytophthora species in marine environments are discussed.

► Two Phytophthora species were isolated from halophilic Zostera marina plants.
► Both species were characterized on morphology, isozyme patterns and ITS sequences.
► One species was identified as Phytophthora inundata, known from freshwater habitats.
► Phytophthora inundata was found for the first time in a marine environment.
► The second Phytophthora was new, and is described here as a new species.