In 2004, Phytophthora symptoms were observed on two different fir species used for Christmas trees in Norway. Isolations resulted in a Phytophthora sp. related to P. inundata from relatively newly established Nordmann fir (Abies nordmanniana) and P. megasperma from seven-year-old subalpine fir (A. lasiocarpa). The Nordmann fir plantation was more severely damaged, with approximately 70% of the trees dead or dying. In the field with subalpine fir, approximately 25% of the trees had yellow or brown foliage and stem canker. Pathogenicity was proven for both Phytophthora isolates on seedlings from their respective host plants. The massive infestation in the Nordmann fir plantation approximately one year after planting suggests that the pathogen was introduced into the planting with the transplants. Except for a recent report of P. cambivora on noble fir (A. procera) produced for bough production (17), Phytophthora has never been reported before on fir in Norway. Accepted for publication 2 October 2006. Published 19 January 2007.

In the annual Norwegian Phytophthora ramorum survey in 2009, wild bilberry samples, collected during September and October in a semimanaged park (arboretum) in the southwest coast of Norway, tested positive in a P. ramorum-specific real-time PCR test (1). Necrotic lesions were observed in shoot tips, branching points, and around leaf abscission scars. The lesions were of variable dimensions. In the samples collected in October, some lesions were confluent and completely covered some shoots. After direct detection on plant material, P. ramorum was isolated from necrotic lesions of the stems on semiselective media PARP (corn meal agar amended with pimaricin, ampicillin, rifampicin, and pentacloronitrobenzene) (2). The isolates were identified by the production of abundant chlamydospores on agar and deciduous, semipapillate sporangia that is characteristic of P. ramorum (3). Sexual structures were not observed. Three pure cultures obtained from different plant samples also tested positive for P. ramorum by the specific real-time PCR test (1). All positive samples were found in close vicinity of infected rhododendron plants. In this location, P. ramorum had already been detected on rhododendron in 2005. A pathogenicity test was performed with two isolates from bilberry and one from rhododendron. Wild asymptomatic bilberry plants were collected at the end of June in the forest around Oslo. Two shoot tips with 6 to 10 leaves each and one small part of a branch with several shoots and immature berries were used for testing each isolate. The inoculations were made by dipping the shoots in a zoospore suspension (2 to 3 × 104 zoospores ml–1) for 1 min. Inoculated material was placed in moist incubation chambers and incubated at room temperature (19 to 24°C). Controls were obtained by dipping shoots in sterile water. After 2 days, lesions were observed on leaf laminae from all the shoots inoculated with the three different isolates. After 4 days, severe petiole necroses were observed and leaves abscised easily from the stems. Symptoms on the stems were observed in the apical part or areas around the nodes. Some shoots were almost completely necrotic. Heavy sporulation was observed on the berries. P. ramorum was reisolated from leaves and stems of inoculated shoots for all the isolates. P. ramorum was not recovered from control plants. To our knowledge, this is the first report of P. ramorum on bilberry in Norway. References: (1) K. L. Hughes et al. Phytopathology 96:975, 2006. (2) M. E. Kannwischer and D. J. Mitchell. Phytopathology 68:1760, 1978. (3) S. Werres et al. Mycol. Res.105:1155, 2001.

In 2004, damages resembling those caused by Phytophthora spp. were observed in a 15-year-old bough plantation of noble fir (Abies procera). When removing bark upward from the roots and base of a diseased tree, a reddish brown discoloration with distinct borders to surrounding wood appeared. The discoloration extended approximately 1.5 m above ground, but only on one side of the stem. This resulted in dead basal branches (flagging) on the cankered side of the tree. Other dying trees in the same field did not show flagging symptoms but turned chlorotic to brown after being girdled by the expanding stem canker. Approximately 25% of the trees were dead or dying. Isolations were carried out from the area between healthy and diseased tissue both from roots and base of the stem of the tree with flagging symptoms. Samples were rinsed in running tap water and plated on the Phytophthora selective medium PARP (17 g of cornmeal agar, 10 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, and 100 mg of pentachloronitrobenzene (PCNB) in 1 liter of water), with and without hymexazol added (50 mg/l). Morphological characters of the isolated Phytophthora sp. included nonpapillate sporangia (37 to 64 μm), internal proliferation, and characteristic hyphal swellings. The isolate was heterothallic and produced amphigynous antheridia when crossed with tester strains of P. cryptogea. The mating type was A2. The internal transcribed spacer (ITS) rDNA sequences were identical to P. cambivora (GenBank Accession No. AY880985). Thus, both morphological characters and DNA analysis supported the species identification. A pathogenesis test to fulfill Koch's postulate was carried out during 2005. Inoculation was done by placing agar with culture in the growth medium close to the roots of noble fir seedlings. Eleven weeks after inoculation, clearly visible stem canker symptoms were observed. The ITS sequences of the reisolated Phytophthora sp. were determined and found identical to P. cambivora. P. cambivora was reported to cause root rot and stem canker in a noble fir Christmas tree plantation in the United States (1). P. citricola and P. citrophthora are known to cause problems on Lawson Falsecypress/Port-Orford-cedar (Chamaecyparis lawsoniana) in Norway, but damages by Phytophthora spp. have never been reported in Abies spp. plantations or forest stands in Norway. Currently, we are also working on Phytophthora problems discovered in two different Christmas tree plantations (A. lasiocarpa and A. nordmanniana). Reference: (1) G. A. Chastagner et al. Plant Dis. 79:290, 1995.

In November 2002, Phytophthora ramorum was isolated from Rhododendron catawbiense with wilted branches in a nursery in Bergen. The isolate was identified by characteristic deciduous, semipapillate sporangia, abundance of large chlamydospores, and slow growth (2). The identification was confirmed by ITS rDNA sequencing. After the first detection, the Norwegian Food Safety Authority (NFSA) started a survey of different ornamental plants during 2003. Of 21 samples from 10 locations, two rhododendron samples were positive. The rhododendron plants containing positive samples in 2002 and 2003 had been imported that same year as the disease was detected on them. In 2003, NFSA made regulations similar to those in the EU for P. ramorum, including the destruction of all infected plants and all plants susceptible to P. ramorum within a 2-m distance of the infected ones. The production of rhododendron in Norwegian nurseries is limited, and most rhododendrons marketed in the country are imported from March to May from other European countries. The main sale of rhododendron occurs in May and June, often before symptoms of P. ramorum are easy to observe. In 2004, 133 samples from 53 locations were analyzed. P. ramorum was found in 29 new locations. It was detected in 57 samples of rhododendron, in one sample of Pieris japonica, and one of Kalmia sp. Symptoms on pieris were similar to those on rhododendron with blighted twigs and leaf spots. In Kalmia sp., P. ramorum was isolated from small foliar spots. In 2005, special efforts were directed to detect P. ramorum before the spring sale. Between January and May, 142 samples were analyzed (including plants from 45 import shipments) and 19 yielded positive (including six samples from five import shipments). In 2005, 370 samples from 74 nurseries and garden centers were analyzed and 97 samples from 43 locations were positive (all were rhododendron). Ten of the 43 locations had been positive in 2004. Some of the samples that yielded positive in the summer and autumn came from import shipments or nurseries controlled earlier and found free from P. ramorum. As suggested previously, the disease is probably moving in trade as symptom-free plants (1) and also likely in batches with few infected plants with mild infections that are difficult to detect when random control is carried out in large shipments. Most nurseries receive new plants every year. It is thus difficult to determine if it is a reintroduction or an eradication failure when a nursery yields positive to P. ramorum in two consecutive years. In 2005, P. ramorum was detected on well-established Viburnum fragrans and rhododendron plants in a private garden in Bergen. The viburnum plants of this garden were heavily infected, with wilting of whole branches from the root collar to the top. The pathogen was also found on established rhododendron shrubs in four public greens in Bergen and two in Stavanger. The two cities are located at the southwestern coast of Norway and have more than 2,000 mm of annual precipitation, cool summers, and mild winters. The pathogenicity of 26 isolates from rhododendron, one from pieris, and one from Kalmia sp. was tested by placing mycelial plugs (18 isolates) or drops of zoospore suspension (7 isolates) on the unwounded abaxial surface of rhododendron leaves of cv. Cunninghams White. After 7 days, all isolates produced lesions larger then 2 cm at each inoculation site. P. ramorum was reisolated from the leaves. References: (1) C. M. Brassier et al. Mycol Res. 108:1107, 2004. (2) S. Werres et al. Mycol. Res. 105:1155, 2001.

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