Susceptibility to Phytophthora ramorum in a key infectious host: landscape variation in host genotype, host phenotype, and environmental factors

Authors

  • Brian L. Anacker,

    1. Department of Geography & Earth Sciences, University of North Carolina, Charlotte, Colvard 5062, Charlotte, NC 28223, USA;
    2. Department of Biology, Sonoma State University, Rohnert Park, CA 94928, USA;
    3. Present address: Department of Environmental Science and Policy, 1 Shields Avenue, University of California, Davis, CA 95616, USA
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  • Nathan E. Rank,

    1. Department of Biology, Sonoma State University, Rohnert Park, CA 94928, USA;
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  • Daniel Hüberli,

    1. Department of Environmental Science Policy & Management, 137 Mulford Hall, University of California, Berkeley, CA 94720, USA;
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  • Matteo Garbelotto,

    1. Department of Environmental Science Policy & Management, 137 Mulford Hall, University of California, Berkeley, CA 94720, USA;
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  • Sarah Gordon,

    1. Department of Biology, Sonoma State University, Rohnert Park, CA 94928, USA;
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  • Tami Harnik,

    1. Department of Environmental Science Policy & Management, 137 Mulford Hall, University of California, Berkeley, CA 94720, USA;
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  • Richard Whitkus,

    1. Department of Biology, Sonoma State University, Rohnert Park, CA 94928, USA;
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  • Ross Meentemeyer

    1. Department of Geography & Earth Sciences, University of North Carolina, Charlotte, Colvard 5062, Charlotte, NC 28223, USA;
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Author for correspondence:
Brian L. Anacker
Tel:+1 530 752 3940
Fax:+1 530 752 3350
Email: blanacker@ucdavis.edu

Summary

  • • Sudden oak death is an emerging forest disease caused by the invasive pathogen Phytophthora ramorum. Genetic and environmental factors affecting susceptibility to P. ramorum in the key inoculum-producing host tree Umbellularia californica (bay laurel) were examined across a heterogeneous landscape in California, USA.
  • • Laboratory susceptibility trials were conducted on detached leaves and assessed field disease levels for 97 host trees from 12 225-m2 plots. Genotype and phenotype characteristics were assessed for each tree. Effects of plot-level environmental conditions (understory microclimate, amount of solar radiation and topographic moisture potential) on disease expression were also evaluated.
  • • Susceptibility varied significantly among U. californica trees, with a fivefold difference in leaf lesion size. Lesion size was positively related to leaf area, but not to other phenotypic traits or to field disease level. Genetic diversity was structured at three spatial scales, but primarily among individuals within plots. Lesion size was significantly related to amplified fragment length polymorphism (AFLP) markers, but local environment explained most variation in field disease level.
  • • Thus, substantial genetic variation in susceptibility to P. ramorum occurs in its principal foliar host U. californica, but local environment mediates expression of susceptibility in nature.

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