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    Author(s): Tyler B. Bourret; Kamyar Aram; Heather K. Mehl; David M. Rizzo; Suzanne Rooney-Latham; Tedmund J. Swiecki; Elizabeth A. Bernhardt; Susan J. Frankel
    Date: 2020
    Source: Proceedings of the seventh sudden oak death science and management symposium: healthy plants in a world with <em>Phytophthora</em>. Gen. Tech. Rep. PSW-GTR-268
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (295.0 KB)

    Description

    Phytophthora diseases in landscapes have gained prominence during the 21st century, due to an increase in Phytophthora surveys and a greater focus on species-level diagnostics. Concurrently, the number of known Phytophthora species has increased from about 60 in 1996 to more than 300 today. In addition to entirely novel species being discovered, many of the most common and well-known 20th century species have been revealed to represent species complexes and are rapidly being divided into new taxa. Beyond the increasingly large Phytophthora, two Phytophthora-like related genera, Calycofera and Nothophytophthora were described in 2017.

    Herein are presented nine novel species of Phytophthora and one novel Nothophytophthora species recently isolated from California. Each species is provisionally described by demonstrating it to be phylogenetically distinct from all other named species based on analysis of ITS rDNA and COX1 mtDNA sequences, the two barcoding loci used for Phytophthora species-level identification. Some species appear to be cryptic species within well-known complexes; these taxa are also found outside of California based on the geographic sources of publicly deposited sequence data. For other species, there is no evidence that they have ever been previously isolated. Whether these new species represent endemic Californian pathogens, longterm residents or recent invaders is unknown.

    Two novel species are presented in Phytophthora clade 2: Phytophthora sp. aureomontensis is a member of the P. citricola species complex only known from California and Oregon coastal streams. Phytophthora taxon eriodictyon is a member of the P. citrophthora species complex that appears to be moving worldwide via the nursery trade; this species is known in California only from restoration outplantings. Phytophthora sp. cadmea is a novel species in clade 7a also baited from restoration areas. Phytophthora taxon wysteria, also a member of clade 7 was isolated from a commonly planted ornamental. Phytophthora taxon agrifolia represents a novel sub-clade within the vast clade 8. Two novel species are presented in clade 9, one of which, Phytophthora taxon xguadalupesoil, appears to be an interspecific hybrid. Phytophthora taxon juncus is closely related to the only other member of clade 11, Phytophthora lilii, while Phytophthora taxon mugwort represents its own subgeneric clade, clade 13. Nothophytophthora taxon umbellularia is known only from a single isolate, baited from a North coast creek with a California bay laurel (Umbellularia californica) leaf.

    Although provisional, naming these taxa and depositing their barcoding sequences into public databases provides vital information to the worldwide Phytophthora diagnostics community about the distribution and movement of these potentially pathogenic and invasive organisms. More systematic work, including morphological characterizations and pathogenicity tests are needed to more fully characterize these provisional species, and live strains will be deposited in culture collections. Nevertheless, because the direct comparison of DNA sequences represents the most tractable and reliable way to compare Phytophthora isolates across space and time, this initial step serves to inform the scientific and regulatory communities of the existence of these species.

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    Citation

    Bourret, Tyler B.; Aram, Kamyar; Mehl, Heather K.; Rizzo, David M.; Rooney-Latham, Suzanne; Swiecki, Tedmund J.; Bernhardt, Elizabeth A.; Frankel, Susan J. 2020. Ten new provisional species of Phytophthora and Nothophytophthora from California. In: Frankel, Susan J.; Alexander, Janice M., tech. cords. Proceedings of the seventh sudden oak death science and management symposium: healthy plants in a world with Phytophthora. Gen. Tech. Rep. PSW-GTR-268. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 46-47.

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https://www.fs.usda.gov/treesearch/pubs/60491