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Phytophthora disease on alder (Alnus spp.) in Norway
G. M. Strømeng1, M. B. Brurberg1, M. L. Herrero1, W. Couanon1, A. Stensvand1,
I. Børja2 and V. Talgø1
1Norwegian Institute for Agricultural and Environmental Research, Ås, Norway; 2Norwegian
Forest and Landscape Institute, Ås, Norway.
gunn-mari.stromeng@bioforsk.no
In 2012, conspicuous dark, bleeding cankers were observed on trunks of dying trees in
natural stands of grey alder (Alnus incana) along the shore of lake Årungen in
Akershus county in Norway. Phytophthora alni, which has been killing alder in Europe
during the past two decades, was suspected to cause the disease. Work was initiated
to identify the causal agent and assess the damage. A survey in the alder population
around the lake, revealed that out of approximately 6000 examined trees, nearly 200
showed typical symptoms on the trunk. At the sites where the damage was most
severe, 20 % of the trees showed symptoms. Samples for isolation of potential
pathogens were collected from the leading edge of canker wounds. The samples were
rinsed in tap water and small pieces were plated on selective medium for Phytophthora
(PARPH). After a few days at room temperature, colonies emerged from the tissue
samples. Subcultures on V8 agar were identified to P. alni ssp. uniformis by PCR using
three primer pairs to identify the subspecies. This is the first time P. alni has been
found in Norway. The same subspecies was also isolated from symptomatic grey and
black alder (A. glutinosa) by a pond located approximately 1 km from the lake.
Symptoms observed on alder at other locations indicate that the disease may be
widespread in south-eastern Norway. By spring 2014, we do not know if there are other
subspecies of P. alni present in Norway, but a survey of Phytophthora on alder will take
place in a larger region later this year to investigate distribution and the possible
presence of other P. alni subspecies.
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