Phytophthora siskiyouensis, a new species from soil and water in southwest Oregon

An unknown Phytophthora species was recovered from rhododendron and tanoak leaf baits used for monitoring streams and soils in Southwestern Oregon for the presence of Phytophthora ramorum. Isolates of this species yielded ITS-DNA sequences that differed substantially from other Phytophthora sequences in GenBank. Morphological features also differed from descriptions of known Phytophthora species. Based on the combination of unique morphology and unique ITS sequences, a new species is proposed. The new species, Phytophthora siskiyouensis, is homothallic, with globose to sub-globose oogonia, which may be terminal, sessile or lateral-intercalary. Antheridia are capitate and mostly paragynous, but sometimes amphigynous. Oospores are mostly aplerotic. Sporangia are ovoid to reniform, with apical, sub-apical, or lateral semi-papillae (occasionally more than one). Sporangia are terminal, sub-terminal, or occasionally intercalary on unbranched sporangiophores, with basal, sub-basal or lateral attachment. Sporangia are weakly deciduous, with variable length pedicels. This combination of characters clearly separates this taxon from other known Phytophthora species. Phytophthora siskiyouensis refers to the geographic region of origin.