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Phytophthora tentaculata and other Phytophthora species introduced into California native habitats via nursery stock
T. J. SWIECKI (1), E. Bernhardt (1), S. Rooney Latham (2), C. Blomquist (2), S. J. Frankel (3), K. Kosta (4). (1) Phytosphere Research, Vacaville, CA, U.S.A.; (2) California Department of Food and Agriculture, Sacramento, CA, U.S.A.; (3) USDA Forest Service, Pacific Southwest Research Station, Albany, CA, U.S.A.; (4) California Department of Food & Agriculture, S

The second detection of <i>Phytophthora</i> <i>tentaculata</i> in the US was in recently-planted toyon (<i>Heteromeles arbutifolia</i>) nursery stock at a habitat restoration site in Alameda Co., California. Subsequent sampling indicated that <i>P.</i> <i>tentaculata</i> was introduced into at least one other site via planting stock from the same nursery. At this second site, <i>P.</i> <i>tentaculata</i> was recovered from <i>Diplacus auriantiacus </i>planted in two successive years, showing that the pathogen could persist in the field from year to year and that symptom expression can be delayed. <i>P.</i> <i>tentaculata</i> was also introduced via material from a different nursery into at least one restoration site in Monterey Co.
Recent sampling shows that <i>Phytophthora</i> spp. have been common in California native plant and restoration nurseries and that <i>Phytophthora</i>-infested plant material is commonly planted into native habitats. In addition to <i>P. tentaculata</i>, we have recovered <i>P. cactorum, P. cambivora, P. cryptogea, P. inundata, P. megasperma, P. nicotianae, P.niederhauserii, P. pini, </i>and<i> P. quercetorum</i> from stock planted in restoration sites. Restoration practitioners have been unfamiliar with <i>Phytophthora</i> root rots and expect mortality in new plantings. Consequently, planting of diseased stock has gone unrecognized. Escape of exotic <i>Phytophthora</i> spp. into native vegetation poses a threat to a wide variety of common and rare species. Planting of infested material directly into habitat can result in permanent habitat degradation.

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