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

Abstract

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.

Functional traits associated with the establishment of introduced Phytophthora spp. in Swedish forests

“…For instance, we did not find P. ramorum in Swedish forests, even though it is able to create asexual survival structures. Indeed, this species has been found established in parks and private gardens in Norway, a country with similar climatic conditions to those found in Sweden (Herrero, Toppe, & Brurberg, ; Ireland, Hardy, & Kriticos, ), supporting the predictive utility of our findings. The absence of P. ramorum in our survey could indicate that it has been recently introduced to Sweden and and has not yet spread further.…”

Oomycete-specific ITS primers for identification and metabarcoding

“…Many oomycete species are important pathogens, causing serious economic losses by infecting vegetables, berries, trees, arthropods and vertebrate animals (Kamoun 2003, Herrero et al 2011. Molecular methods enable rapid identification of pathogens in environmental samples and infected tissues by using specific PCR primers and rapidly evolving high-throughput sequencing (HTS) technologies.…”

Scientific Opinion on the Pest Risk Analysis onPhytophthora ramorumprepared by the FP6 project RAPRA

“…Moreover, inspection data from Norway show that P. ramorum is still present in import consignments with P. ramorum host plants originating in the European Union (Sundheim et al, 2009;Herrero et al, 2010). These data originate from the inspection procedure applied by the Norwegian Food Safety Authority, where import consignments showing suspicious symptoms are sampled for testing.…”