Stream Baiting for Detection of Phytophthora ramorum in Oregon Tanoak Forests, 2013
Alan Kanaskie1, Everett Hansen2, Wendy Sutton2, Paul Reeser2, Ellen Goheen2 and Elizabeth Hooper2
1 = Oregon Department of Forestry, 2 = Oregon State University, 3 = USDA-Forest Service
INTRODUCTION
LOCATION OF STREAM BAITS AND DRAINAGES
Stream monitoring using leaf baits for early detection of Phytophthora
ramorum is an important part of the Oregon Sudden Oak Death (SOD)
program. Forty-eight streams in and near the Oregon quarantine area in
the SW corner of the state were monitored between April 2 and
December 16, 2013. The drainages monitored ranged in size from 20 to
26,995 acres, with a combined area of 145,330 acres.
METHODS
Leaf baits in mesh bag
Infected leaf baits
Rhododendron (Rhododendron macrophyllum) and tanoak
(Notholithocarpus densiflorus) leaf baits in mesh bags were exchanged
every two weeks, except during the federal shutdown in mid-September.
+ - - - +
P. ramorum growing on nutrient medium
DNA gel confirming P. ramorum
Bait leaves were assayed by isolation onto Phytophthora-selective media
(CARP) and Multiplex ITS PCR.
At 11 of the sites we followed the USDA Forest Service National
Protocol for stream baiting. Baits from these sites received an additional
Real-Time PCR assay using COX primers and P. ramorum-specific
primers and probes, validated by USDA APHIS PPQ CPHST.
DETECTION SUMMARY
P. ramorum was recovered from baits in 7 drainages in 2013. Six of
these drainages had confirmed infected tanoaks within the drainage
during 2013 or earlier. The other drainage yielded positive baits (WA84,
WA125) five times in 2013 but infected vegetation has not yet been
found. Stream baiting failed to detect P. ramorum in 3 drainages with
known infected tanoaks.
Two stream baits (WA9, WA12) were located in very small streams that
drained infested sites that underwent eradication treatments (cutting and
burning host vegetation) 10 years ago. P. ramorum was recovered
regularly from these streams throughout 2013 (and previous years),
suggesting an in-stream mode of survival.
P. ramorum was recovered from stream baits in every month (AprilDecember) and at stream temperatures ranging from 47.8 to 57.2
degrees F.
COMPARISON OF METHODS
For the eleven National Protocol streams, PCR tests were better able to detect P. ramorum than
culturing. Of the 31 cases where P. ramorum was detected, it was detected by both PCR and culture
16 times (51%), by PCR-only 14 times (45%) and by culture-only one time (3%). Real Time PCR
appeared to be the most sensitive method; in 8 instances (26%) this method detected P. ramorum
while the other two methods did not.
ACKNOWLEDGEMENTS
Funds were provided by USDA-Forest Service Forest Health Monitoring Program and the Forest
Health Protection Program (Region 6) and the Oregon Department of Forestry. Thanks also to the
USDI-Bureau of Land Management and the many cooperating landowners in Curry county.