Nothophytophthora gen. nov, a new sister genus of Phytophthora from natural and semi-natural ecosystems

During various surveys of Phytophthora diversity in Europe, Chile and Vietnam slow growing oomyceteisolates were obtained from rhizosphere soil samples and small streams in natural and planted forest stands.Phylogenetic analyses of sequences from the nuclear ITS, LSU, β-tubulin and HSP90 loci and the mitochondrialcox1 and NADH1 genes revealed they belong to six new species of a new genus, officially described here asNothophytophthora gen. nov., which clustered as sister group to Phytophthora. Nothophytophthora species sharenumerous morphological characters with Phytophthora: persistent (all Nothophytophthora spp.) and caducous(N. caduca, N. chlamydospora, N. valdiviana, N. vietnamensis) sporangia with variable shapes, internal differentiationof zoospores and internal, nested and extended (N. caduca, N. chlamydospora) and external (all Nothophytophthoraspp.) sporangial proliferation; smooth-walled oogonia with amphigynous (N. amphigynosa) and paragynous(N. amphigynosa, N. intricata, N. vietnamensis) attachment of the antheridia; chlamydospores (N. chlamydospora)and hyphal swellings. Main differing features of the new genus are the presence of a conspicuous, opaque pluginside the sporangiophore close to the base of most mature sporangia in all known Nothophytophthora species andintraspecific co-occurrence of caducity and non-papillate sporangia with internal nested and extended proliferationin several Nothophytophthora species. Comparisons of morphological structures of both genera allow hypothesesabout the morphology and ecology of their common ancestor which are discussed. Production of caducous sporangiaby N. caduca, N. chlamydospora and N. valdiviana from Valdivian rainforests and N. vietnamensis from amountain forest in Vietnam suggests a partially aerial lifestyle as adaptation to these humid habitats. Presence oftree dieback in all forests from which Nothophytophthora spp. were recovered and partial sporangial caducity ofseveral Nothophytophthora species indicate a pathogenic rather than a saprophytic lifestyle. Isolation tests fromsymptomatic plant tissues in these forests and pathogenicity tests are urgently required to clarify the lifestyle of thesix Nothophytophthora species.