First Report of Phytophthora ramorum Causing Shoot Dieback on Bilberry (Vaccinium myrtillus) in Norway.

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.

First Report of Phytophthora ramorum in Ornamental Plants in Norway.

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.

First Report of Root Rot and Stem Canker Caused by Phytophthora cambivora on Noble Fir (Abies procera) for Bough Production in Norway.

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.

First Report of Root Rot and Stem Blight Caused by Phytophthora palmivora in Eustoma grandiflorum.

Eustoma grandiflorum (Raf.) Shinn., commonly referred to as Lisianthus or Texas bluebell, is grown on a limited but increasing scale in Norwegian greenhouses. In autumn 1999, E. grandiflorum plants with brown rotten roots and wilting foliage were collected from a cut-flower production facility in southeastern Norway. Symptoms were difficult to distinguish from those caused by Pythium spp. or early attack of Fusarium spp. For diagnosis, root and stem segments surface sterilized by dipping in alcohol and hypochlorite were plated on potato dextrose agar. Phytophthora sp. was isolated consistently from diseased roots and stems. Suspected Phytophthora sp. isolates were transferred to selective agar medium containing hymexazol and identified by morphological characteristics and DNA sequence homology (1). The fungus was characterized by stellate mycelium, lack of oogonia in single culture, sympodial sporangiophores, and production of numerous papillate, ellipsoid sporangia that were caduceus with small pedicels in water. Optimum temperature for mycelium growth was 25 to 30°C, with limited growth at 10 and 35°C. The DNA sequence of the polymerase chain reaction amplified internal transcribed spacer (ITS1 and ITS2) regions of rDNA, confirmed the identification as P. palmivora. Pathogenicity studies were conducted by inoculating nine, 12-week-old E. grandiflorum plants grown in 10-cm pots with peat substrate at 24°C with artificial light (120 W/m2) for 10 h per day, with a zoospore suspension or an agar piece toward the plant stem. The pathogenicity study was repeated once. In both experiments, all plants except uninoculated controls, died within 3 weeks after inoculation. P. palmivora was reisolated from diseased plants. In later greenhouse experiments, more than 50% of plants showed disease symptoms when adding 1,000 zoospores of P. palmivora per pot. 'Ecco Yellow' was more susceptible than 'Flamenco Purple'. The pathogen was as aggressive as Fusarium avenaceum in pathogenicity studies. Since E. grandiflorum is grown on a limited scale in Norway, we lack experience with the economic impact of this disease in the cut-flower industry. To our knowledge, this is the first report of P. palmivora in E. grandiflorum. Reference: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

First Report of Phytophthora cinnamomi Root Rot, Stem, and Leaf Blight on Ivy.

Phytophthora cinnamomi was isolated from varieties of Hedera helix pot plants in 1989 in two Danish greenhouse nurseries. The symptoms were brown, rotten roots and stems, and brown areas developing from the base of the leaves. The fungus was isolated directly from roots, stems, leaves, and soil, and by baiting the nutrient solutions of the watering systems with needles of Cedrus deodara. The fungus was isolated on Phytophthora selective agar medium containing hymexazol and identified with the keys of Kröber (1) and Stamps et al. (2). The fungus was characterized by coralloid hyphal swellings, chlamydospores, lack of oogonia in single culture, and production of numerous, ovoid sporangia with a nonpapillate, wide pore. The sporangia produced many zoospores after 2 days flooding with autoclaved pond water on V8 juice agar, followed by internal proliferation. The fungus was also isolated in Norway in 1993 from ivy pot plants. The fungus was widespread in Danish and Norwegian pot plant nurseries in 1997 and caused losses in most varieties, especially at temperatures above 23°C. Effective fungicides are not available for use in Denmark and the disease is easily spread with cuttings, and through the watering system with recirculation of the nutrient solution. A Danish isolate of P. cinnamomi originating from roots of H. helix was used in a pathogenicity test. Five-week-old cuttings were inoculated by adding zoospores (5 per ml) to the recirculating nutrient solution. Control plants were on a separate bench with nutrient solution without the fungus. After 1 week, symptoms of root rot were observed, and 2 weeks after inoculation, 75% of plants expressed severe symptoms on roots, stems, and leaves. P. cinnamomi was reisolated from roots, stems, and leaves of diseased plants, but was not isolated from the control plants. The reisolate was morphologically identical to the original isolate. This is the first report of P. cinnamomi from ivy in Europe. References: (1) H. Kröber. Mitt. Biol. Bundesanst. Land Forstwirtsch. Berlin-Dahlem 225:73, 1985. (2) D. J. Stamps et al. 1990. Mycol. Pap. No. 162. CAB Int. Mycol. Inst., Kew, England.