Phytophthora obscura sp. nov., a new species of the novel Phytophthora subclade 8d

Authors

  • N. J. Grünwald,

    Corresponding author
    1. Horticultural Crops Research Laboratory (HCRL), USDA ARS, 3420 NW Orchard Ave., Corvallis, OR 97330, USA
      E-mail: Nik.Grunwald@ars.usda.gov
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  • S. Werres,

    1. Julius Kühn Institute - Federal Research Centre for Cultivated Plants (JKI), Institute for Plant Protection in Horticulture and Forests, Messeweg 11/12, 38104 Braunschweig, Germany
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  • E. M. Goss,

    1. Horticultural Crops Research Laboratory (HCRL), USDA ARS, 3420 NW Orchard Ave., Corvallis, OR 97330, USA
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    • Present address: Department of Plant Pathology and Emerging Pathogens Institute, University of Florida, PO Box 110680, Gainesville, FL, 32611, USA.

  • C. R. Taylor,

    1. Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331, USA
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  • V. J. Fieland

    1. Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331, USA
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E-mail: Nik.Grunwald@ars.usda.gov

Abstract

A new Phytophthora species was detected (i) in the USA, infecting foliage of Kalmia latifolia, (ii) in substrate underneath Pieris, and (iii) in Germany in soil samples underneath Aesculus hippocastanum showing disease symptoms. The new species Phytophthora obscura sp. nov. is formally named based on phylogenetic analysis, host range, Koch’s postulates and morphology. Phytophthora obscura is homothallic with paragynous antheridia and semipapillate sporangia. It is genetically closely related to P. syringae and P. austrocedrae and together these three species define a new Phytophthora subclade 8d, with significant support for all genetic loci analysed including seven nuclear genes and the mitochondrial gene coxII. The morphological and ecological characteristics are very similar to P. syringae, and it is likely that P. obscura was not described earlier because it was identified as P. syringae. Artificial inoculations indicated that horse chestnut, kalmia, pieris and rhododendron might be hosts, and Koch’s postulates were confirmed for kalmia from which it was isolated. This pathogen was named after its elusive nature since it has to date rarely been detected in the US and Germany.

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