|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.