Alder Phytophthora

(Phytophthora alni subsp. uniformis) in Alaska

contact: Lori Winton

Please see the following materials for a more through discussion:

Current Map as of February 20, 2009

 

map - Phytophthora sample sites
 

February 2009 update

As of February 20, 2009, more isolates of PAU have been found, now a total of 28 since 2007. The new findings expand the map of PAU (+) locations to eleven sites. Four new sites added in February include sites 6 and 70 (both near Fairbanks), site 61 (near Tok), and site 81 (Kenai Peninsula). These findings include isolates mainly from soil baits beneath alders, but also at least one from a stream bait in the Tanana River. The distribution pattern of the PAU (+) sites across over 1,000 miles of road is strongly suggestive of the distribution of a native pathogen. Testing of these isolates and comparisons with PAU isolates from Europe is underway to determine whether the organism is native or introduced in Alaska.

By January, fourteen isolates of the new unnamed Phytophthora species in Clade 8C were found at a single location, Quartz Creek, on the Kenai Peninsula. Phytophthora gallica and Phytophthora pseudosyringae, both known pathogens of European alders, have also been isolated from several sites. Pathogenicity testing is underway for these unique Phytophthora spp. findings at Oregon State University. We have no field evidence, however, that Phytophthora species are causing root disease or are involved in the dieback and mortality of alder in Alaska.

As processing of the 2008 samples from Alaska continues, we expect to report more findings of Phytophthora alni subspecies uniformis (PAU), the unnamed new Phytophthora species in Clade 8C, and other unique Phytophthora findings.

"For more information, contact Lori Trummer, Pathologist, ltrummer@fs.fed.us.

January 2009 update

"As processing of the 2008 samples from Alaska continues, we expect to report more findings of Phytophthora alni subspecies uniformis (PAU), the unnamed new Phytophthora species in Clade 8C, and other unique Phytophthora findings.

As of January 9, 2009, several more isolates of PAU have been found, now a total of 10 since 2007. The new findings expand the map of PAU (+) locations to seven sites. Two new sites added for January include sites 66 and 72, both near Fairbanks. Site 66 is the first time that PAU was isolated from a stream bait. All other findings have been from soil baits beneath alders. The distribution pattern of the seven PAU (+) sites across over 1,000 miles of road is suggestive of a native pathogen distribution. Testing of these isolates is underway to determine whether the organism is native or introduced.

Fourteen isolates of the new unnamed Phytophthora species in Clade 8C have been found, all from a single location, Quartz Creek, on the Kenai Peninsula. Phytophthora gallica and Phytophthora pseudosyringae, both known pathogens of European alders, have also been isolated from several sites. Pathogenicity testing is underway for these unique Phytophthora spp. findings at Oregon State University. We have no field evidence, however,
that Phytophthora species are causing root disease or are involved in the dieback and mortality of alder in Alaska.

December 2008 update

As processing of the 2008 samples from Alaska continue, we expect to report more findings of both Phytophthora alni subspecies uniformis (PAU) and the unnamed new Phytophthora species in Clade 8C.

As of December 15, 2008, several more isolates of PAU have been found, now a total of 8 since 2007. The new findings substantially expand the current map of PAU (+) locations to five sites. Testing of these isolates is underway to determine whether the organism is native or introduced.

Additionally, more isolates of the new unnamed Phytophthora species, now 12, have been found. All still have been found from a single location, Quartz Creek, on the Kenai Peninsula.

Briefing Paper: 2008 findings from Alaska
A new species of Phytophthora related to P. ramorum, and more isolates of P. alni subsp. uniformis

New Findings:
A putative new species of Phytophthora previously unknown to science was found in Alaska during riparian Phytophthora surveys and confirmed in November 2008 by Dr. Gerard Adams, Michigan State University.

The Alaska Phytophthora was sent to the USDA APHIS-PPQ Plant Safeguarding and Pest Identification, National Identification Services Molecular Diagnostics Laboratory and also to Dr. Everett Hansen, Oregon State University. Both labs have analyzed DNA sequences of the ITS-rDNA and COX I & II regions and reached the conclusion that the unique sequence identifies this isolate as a member of Clade 8C, the P. ramorum/P. lateralis clade, but as a new member. The APHIS Lab and Dr. Hansen’s Lab will assist with confirmation of morphological identification of the new species.

Dr. Adams has also found three more isolates of P. alni subsp. uniformis (PAU) in his first sequencing of the 2008 collections.

More from November briefing... (PDF)

Phytophthora alni subsp. uniformis found in Alaska beneath thinleaf alders - Accepted for publication in Plant Health Progress October 2008

Phytophthora alni subsp. uniformis (PAU) was isolated from soil beneath alder from two riparian areas in 2007; one area was in south-central and one in interior Alaska. This is the first time this hybrid pathogen has been found in North America. Alder Phytophthora, primarily subsp. alni (PAA), is a well documented lethal root and collar disease of alder in nearly a dozen European countries. The PAU subspecies, however, is considered less aggressive than PAA, though our understanding of this is evolving. Finding PAU in two remote, unmanaged locations in Alaska is surprising and perplexing; the threat to Alaskan alder from this pathogen is unknown. No root or root collar symptoms of this pathogen have been noted in Alaska. Perhaps PAU has co-existed benignly in Alaska with alder and has not been noted due to the lack of surveys such as those conducted in 2007. Monitoring and research related to this pathogen is continuing in 2008.

see the full briefing...

Fact sheet

The US Forest Service, APHIS and Alaska Division of Agriculture compiled a brief one page synopsis for PAU. Please see this "fact sheet" for a basic outline of current knowledge. This synopsis also addresses questions concerning 1) recognizing the pathogen, 2) risk for alder in Alaska, and 3) what the next steps should be.

March 2008 Update

On February 29, the APHIS’ New Pest Advisory Group (NPAG) issued the following official
recommendations for Phytophthora alni, alder root rot:

  1. The NPAG recommends no change in the PPQ policy regarding Phytophthora alni, retain as reportable/actionable, and list P. alni as such in the Pest ID database. Action Leader: Joe Cavey, PPQNIS.
  2. The NPAG recommends that PPQ establish a list of Phytophthora of concern to the United States and require offshore testing for these species with negative results documented on a phytosanitary certificate prior to any susceptible host entering the United States. CPHST will develop this list in collaboration with Matt Royer (EDP), Bill Alley (PRI), and others. When the new Q37 regulation is finalized, hosts of Phytophthora of concern to the United States will be placed on the Not Allowed Pending Risk Assessment (NAPRA) list. Action Leader: Kim Schwartzburg, PPQCPHST.
  3. The NPAG recommends adding Phytophthora alni to a list of Phytophthora of concern to the
    United States. Action Leader: Kim Schwartzburg, PPQCPHST.
  4. The NPAG recommends incorporating Phytophthora alni into a New Pest Response Guideline that will address Phytophthora of concern to the United States. Action Leader: Russ Bulluck, PPQEDP.

Baiting Methodology for 2007 Phytophthora surveys in Alaska

Dr. Gerry Adams, Michigan State University

At thirty streams in Alaska, Phytophthora species were baited and trapped from roots, soils, and water sources using Rhododendron leaves.

rhododendron leaves in bag as bait

Baits with Rhododendron leaves.

 
  • Following a 48 hour incubation, the baits were removed from contact with the plants, soils, and water. They were washed and incubated at room temperature to 17 C, depending on resources.
  • The soil was placed in styrofoam bowls and saturated. Three rhododendron leaves were placed on each and incubated up to 7 days.
  • As lesions formed over 7-days, isolations from the margins of lesions were transferred to Phytophthora selective medium.
  • From these media, isolates were transferred to V-8 juice medium containing B-sitosterol to stimulate formation of morphologically informative sexual spores (oospores).
  • Later, plugs from these plates were floated in soil-extract to stimulate formation of a second type of morphologically informative spore producing organelle (sporangia).
  • Permanent slide mounts will be prepared of the oospores and sporangia and used in microscopic studies and vouchers in conventional identification of the Phytophthora species.
  • Additionally, species that are intractable to morphological identification such as P. gonapodyides will be identified based in DNA sequence homology to identified reference strains in NBCI Genbank data repository.
affected alder

Panguigue Creek, one of the two positive Phytophthora alni subsp. uniformis sites in Alaska.