First record of Phytophthora alni in Alaska, USA
Surveys were initiated in 2007/2008 to identify the possible causes of the widespread dieback and mortality which is currently being observed on Alnus incana subsp. tenuifolia (thinleaf alder) across South-Central and Interior Alaska (US). More than 500 isolates of Phytophthora and Pythium species were recovered from baiting watercourses or saturated rhizosphere soil. Phytophthora alni subsp. uniformis (formerly EPPO Alert List) was recovered from soil samples collected beneath alder trees in the Kenai Peninsula, through Anchorage and up to Fairbanks in the North. As of February 2009, P. alni subsp. uniformis was isolated in 11 sites. During these studies other Phytophthora species were also recovered: P. gonapodyides, P. megasperma, P. pseudosyringae, P. gallica, and an unknown Phytophthora species. This is the first time that P. alni is reported from North America but further studies are needed to better understand its possible role in the alder disease, as other pathogens could also be involved (e.g. Valsa or Cytospora spp.). It is stressed that for the moment there is no field evidence that Phytophthora species are causing root disease or are involved in the dieback and mortality of alder in Alaska. Studies are also needed to determine the possible origins of these new Phytophthora species in Alaska (i.e. are they native or introduced exotic species?).
Adams GC, Catal M, Trummer L, Hansen EM, Reeser P, Worrall JJ (2008) Phytophthora alni subsp. uniformis found in Alaska beneath thinleaf alders. Plant Health Progress. http://www.forestpathology.org/pdfs/adams2008Palni.pdf
Trummer L (2009) Alder Phytophthora (Phytophthora alni subsp. uniformis) in Alaska. http://www.fs.fed.us/r10/spf/fhp/phytophthora/uniformis.html