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

Abstract

During various surveys of <i>Phytophthora</i> diversity in Europe, Chile and Vietnam slow growing oomycete isolates 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 <i>HSP90</i> loci and the mitochondrial <i>cox1</i> and <i>NADH1</i> genes revealed they belong to six new species of a new genus, officially described here as <i>Nothophytophthora</i> gen. nov., which clustered as sister group to <i>Phytophthora</i>. <i>Nothophytophthora</i> species share numerous morphological characters with <i>Phytophthora</i>: persistent (all <i>Nothophytophthora</i> spp.) and caducous (<i>N. caduca</i>, <i>N. chlamydospora</i>, <i>N. valdiviana</i>, <i>N. vietnamensis</i>) sporangia with variable shapes, internal differentiation of zoospores and internal, nested and extended (<i>N. caduca</i>, <i>N. chlamydospora</i>) and external (all <i>Nothophytophthora</i> spp.) sporangial proliferation; smooth-walled oogonia with amphigynous (<i>N. amphigynosa</i>) and paragynous (<i>N. amphigynosa</i>, <i>N. intricata</i>, <i>N. vietnamensis</i>) attachment of the antheridia; chlamydospores (<i>N. chlamydospora</i>) and hyphal swellings. Main differing features of the new genus are the presence of a conspicuous, opaque plug inside the sporangiophore close to the base of most mature sporangia in all known <i>Nothophytophthora</i> species and intraspecific co-occurrence of caducity and non-papillate sporangia with internal nested and extended proliferation in several <i>Nothophytophthora</i> species. Comparisons of morphological structures of both genera allow hypotheses about the morphology and ecology of their common ancestor which are discussed. Production of caducous sporangia by <i>N. caduca</i>, <i>N. chlamydospora</i> and <i>N. valdiviana</i> from Valdivian rainforests and <i>N. vietnamensis</i> from a mountain forest in Vietnam suggests a partially aerial lifestyle as adaptation to these humid habitats. Presence of tree dieback in all forests from which <i>Nothophytophthora</i> spp. were recovered and partial sporangial caducity of several <i>Nothophytophthora</i> species indicate a pathogenic rather than a saprophytic lifestyle. Isolation tests from symptomatic plant tissues in these forests and pathogenicity tests are urgently required to clarify the lifestyle of the six <i>Nothophytophthora</i> species.