| Summary: | Since 1999, an unusual <i>Phytophthora</i> species has repeatedly been found associated with stem lesions and root and collar rot on young olive trees in Southern Italy. In all cases, this species was obtained from recently established commercial plantations or from nursery plants. Morphologically, the <i>Phytophthora</i> isolates were characterized by the abundant production of caducous non-papillate conidia-like sporangia (pseudoconidia) and caducous papillate sporangia with a short pedicel, resembling <i>P. palmivora</i> var. <i>heterocystica</i>. Additional isolates with similar features were obtained from nursery plants of <i>Ziziphus spina-christi</i> in Iran, <i>Juniperus oxycedrus</i> and <i>Capparis spinosa</i> in Italy, and mature trees in commercial farms of <i>Durio zibethinus</i> in Vietnam. In this study, morphology, breeding system and growth characteristics of these <i>Phytophthora</i> isolates with peculiar features were examined, and combined mitochondrial and nuclear multigene phylogenetic analyses were performed. The proportion between pseudoconidia and sporangia varied amongst isolates and depended on the availability of free water. Oogonia with amphigynous antheridia and aplerotic oospores were produced in dual cultures with an A2 mating type strain of <i>P. palmivora</i>, indicating all isolates were A1 mating type. Phylogenetically, these isolates grouped in a distinct well-supported clade sister to <i>P. palmivora</i>; thus, they constitute a separate taxon. The new species, described here as <i>Phytophthora heterospora</i> sp. nov., proved to be highly pathogenic to both olive and durian plants in stem inoculation tests.
|
|---|