scholarly journals Response of Selected Nursery Crop Plants to Inoculation with Isolates of Phytophthora ramorum and Other Phytophthora Species

2006 ◽  
Vol 16 (2) ◽  
pp. 216-224 ◽  
Author(s):  
R.G. Linderman ◽  
E.A. Davis ◽  
J.L. Marlow
Keyword(s):  
Plant Species ◽  
The United States ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Experimental Conditions ◽  
Pathogen Virulence ◽  
Detached Leaves ◽  
Nursery Crops ◽  
Relative Differences ◽  
Selection Of

Many nursery crops are susceptible to root and foliage diseases caused by numerous species of Phytophthora. Phytophthora ramorum causes sudden oak death of trees and ramorum leaf blight and shoot dieback on numerous nursery plants, including rhododendron (Rhododendron spp.), viburnum (Viburnum spp.), pieris (Pieris spp.), and camellia (Camellia spp.) in Europe, the United States, and British Columbia, Canada. We sought to evaluate relative susceptibility of a selection of ornamental nursery crops by inoculating detached leaves with several species of Phytophthora known to infect rhododendrons, and to compare the relative virulence on those species to isolates of P. ramorum. The results indicated that many plants were susceptible under these experimental conditions, while others were not. On a given host, symptoms caused by all species of Phytophthora were identical except for differences in pathogen virulence. Plant species were identical except for differences in pathogen virulence. Plant species within genera or cultivars within species varied in susceptibility to isolates of P. ramorum and other species of Phytophthora. Phytophthora ramorum, P. citricola, P. citrophthora, and P. nicotianae were the most virulent pathogens on most of the host plants inoculated. Some plants were susceptible to several species of Phytophthora, while others were susceptible only to P. ramorum. Inoculation of detached leaves of `Nova Zembla' rhododendron, lilac (Syringa vulgaris), or doublefile viburnum (Viburnum plicatum var. tomentosum) under controlled conditions with different species of Phytophthora or isolates of P. ramorum (both mating types) indicated significant relative differences in species or isolate virulence.

scholarly journals First Report of Phytophthora hydropathica Causing Wilting and Shoot Dieback on Viburnum in Italy

Plant Disease ◽  
2014 ◽  
Vol 98 (11) ◽  
pp. 1582-1582 ◽  
Author(s):  
S. Vitale ◽  
L. Luongo ◽  
M. Galli ◽  
A. Belisario
Keyword(s):  
Natural Infection ◽  
Morphological Characteristics ◽  
Leaf Tissue ◽  
The United States ◽  
Selective Medium ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Width Ratio ◽  
Morphological Identification ◽  
First Report

The genus Viburnum comprises over 150 species of shrubs and small trees such as Laurustinus (Viburnum tinus L.), which is one of the most widely used ornamental plants in private and public gardens. Furthermore, it commonly forms stands of natural woodland in the Mediterranean area. In autumn 2012, a survey was conducted to determine the presence of Phytophthora ramorum on Viburnum in commercial nurseries in the Latium region where wilting, dieback, and death of twigs were observed on 30% of the Laurustinus plants. A Phytophthora species was consistently recovered from soil rich in feeder roots from potted Laurustinus plants showing symptoms. Soil samples were baited with rhododendron leaves. Small pieces of leaf tissue cut from the margin of lesions were plated on P5ARPH selective medium (4). Pure cultures, obtained by single-hypha transfers on potato dextrose agar (PDA), were petaloid. Sporangia formation was induced on pepper seeds (3). Sporangia were almost spherical, ovoid or obpyriform, non-papillate and non-caducous, measuring 36.6 to 71.4 × 33.4 to 48.3 μm (average 53.3 × 37.4 μm) with a length/width ratio of 1.4. Chlamydospores were terminal and 25.2 to 37.9 μm in diameter. Isolates were considered heterothallic because they did not produce gametangia in culture or on the host. All isolates examined had 30 to 35°C as optimum temperatures. Based on these morphological characteristics, the isolates were identified as Phytophthora hydropathica (2). Morphological identification was confirmed by internal transcribed spacer (ITS), and mitochondrial partial cytochrome oxidase subunit 2 (CoxII) with BLAST analysis in the NCBI database revealing 99% identity with ITS and 100% identity with CoxII. The sequences of the three isolates AB234, AB235, and AB236 were deposited in European Nucleotide Archive (ENA) with the accession nos. HG934148, HG934149, and HG934150 for ITS and HG934151, HG934152, and HG934153 for CoxII, respectively. Pathogenicity tests were conducted in the greenhouse on a total of six 1-year-old shoots cut from V. tinus plants with two inoculation points each. Mycelial plugs cut from the margins of actively growing 8-day-old cultures on PDA were inserted through the epidermis into the phloem. Controls were treated as described above except that sterile PDA plugs replaced the inoculum. Shoots were incubated in test tubes with sterile water in the dark at 24 ± 2°C. After 2 weeks, lesions were evident at the inoculation points and symptoms were similar to those caused by natural infection. P. hydropathica was consistently re-isolated from the margin of lesions, while controls remained symptomless. In the United States in 2008, P. hydropathica was described as spreading from irrigation water to Rhododendron catawbiense and Kalmia latifolia (2). This pathogen can also attack several other horticultural crops (1), but to our knowledge, this is the first report of P. hydropathica causing wilting and shoot dieback on V. tinus. References: (1) C. X. Hong et al. Plant Dis. 92:1201, 2008. (2) C. X. Hong et al. Plant Pathol. 59:913, 2010. (3) E. Ilieva et al. Eur. J. Plant Path. 101:623, 1995. (4) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986.

Comparative Susceptibility of Plants Native to the Appalachian Range of the United States to Inoculation with Phytophthora ramorum

2007 ◽  
Vol 8 (1) ◽  
pp. 12 ◽  
Author(s):  
Robert G. Linderman ◽  
Patricia B. de Sá ◽  
E. Anne Davis
Keyword(s):  
United States ◽  
Plant Species ◽  
Mating Type ◽  
Management Practices ◽  
The United States ◽  
Phytophthora Ramorum ◽  
Eastern United States ◽  
Comparative Susceptibility ◽  
Climatic Characteristics ◽  
Inoculum Type

Phytophthora ramorum, cause of sudden oak death of trees or ramorum blight of other plant species, has an ever-increasing host range. Some geographic regions are considered to be at high risk of becoming infested with the pathogen, possibly causing plant mortality such as seen in native habitats of California and Oregon. One such region is the Appalachian range of the eastern United States, where known susceptible plants occur and climatic characteristics appear favorable for infections by this pathogen. We collected foliage of a range of plant species native to Appalachia in Kentucky during two summer seasons, and the foliage was shipped to Oregon for inoculation with P. ramorum to determine relative susceptibility. Leaves were needle-wounded and inoculated with either mycelium agar plugs or sporangia of a North American (A2 mating type) or European (A1 mating type) isolate. After 14 days incubation at 20°C in moist boxes, lesions caused by either inoculum type or isolate generally were comparable using digital photos and ASSESS software. Some genera, species, and cultivars within species were highly susceptible, while others were moderately susceptible or not susceptible. These results provide a basis for regional surveyors to select target hosts and to generate survey and management practices for nursery and forest areas. Accepted for publication 24 April 2007. Published 17 September 2007.

Evaluation of Chemical Agents for the Control of Phytophthora ramorum and Other Species of Phytophthora on Nursery Crops

2008 ◽  
Vol 9 (1) ◽  
pp. 26 ◽  
Author(s):  
Robert G. Linderman ◽  
E. Anne Davis
Keyword(s):  
Foliar Application ◽  
Management Strategies ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Detached Leaf ◽  
Chemical Agents ◽  
Mycelial Plug ◽  
Previously Treated ◽  
Nursery Crops ◽  
Leaf Test

Phytophthora diseases occur frequently in nurseries, and the recent incidence of ramorum blight, caused by P. ramorum, on nursery crops has underscored the need for improved management strategies against all Phytophthora diseases. We evaluated several chemicals that target Oomycete pathogens, inoculating detached rhododendron or lilac leaves removed from plants previously treated with various chemicals, or chemically-treated leaves on intact plants. Results indicated that Subdue MAXX (drench or foliar application) was the most effective chemical in suppressing infections caused by all species of Phytophthora tested (P. ramorum, P. citricola, P. citrophthora, and P. nicotianae) except P. citrophthora; with P. ramorum, it was active for at least 6 weeks after spray application. More chemicals were effective when sporangial rather than mycelial plug inoculum of P. ramorum was used, including Aliette, Ranman, Stature DM, and Fenamidone. All chemicals tested were fungistatic, not fungicidal. These tests indicate that several materials inhibit infection by Phytophthora species, and that the detached leaf test is effective in evaluating efficacy of chemical agents for the suppression of Phytophthora pathogens from nurseries. Accepted for publication 10 November 2007. Published 11 February 2008.

scholarly journals Phytophthora Genomics: The Plant Destroyers' Genome Decoded

2006 ◽  
Vol 19 (12) ◽  
pp. 1295-1301 ◽  
Author(s):  
Francine Govers ◽  
Mark Gijzen
Keyword(s):  
Gene Annotation ◽  
Draft Genome ◽  
The United States ◽  
Phytophthora Species ◽  
Phytophthora Sojae ◽  
Phytophthora Ramorum ◽  
Department Of Energy ◽  
United States Department ◽  
Sequencing Project ◽  
Energy Joint Genome Institute

The year 2004 was an exciting one for the Phytophthora research community. The United States Department of Energy Joint Genome Institute (JGI) completed the draft genome sequence of two Phytophthora species, Phytophthora sojae and Phytophthora ramorum. In August of that year over 50 people gathered at JGI in Walnut Creek, California, for an annotation jamboree and searched for the secrets and surprises that the two genomes have in petto. This culminated in a paper in Science in September of this year describing the highlights of the sequencing project and emphasizing the power of having the genome sequences of two closely related organisms. This MPMI Focus issue on Phytophthora genomics contains a number of more specialized manuscripts centered on gene annotation and genome organization, and complemented with manuscripts that rely on genomics resources.

scholarly journals First Report of Dieback and Leaf Lesions on Rhododendron sp. Caused by Phytophthora hedraiandra in the United States

Plant Disease ◽  
2006 ◽  
Vol 90 (1) ◽  
pp. 109-109 ◽  
Author(s):  
B. W. Schwingle ◽  
J. A. Smith ◽  
R. A. Blanchette ◽  
S. Gould ◽  
B. L. Blanchette ◽  
...  
Keyword(s):  
United States ◽  
Average Length ◽  
The United States ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Width Ratio ◽  
Its Sequence ◽  
Voucher Specimen ◽  
First Report ◽  
Quercus Species

Surveys for Phytophthora ramorum in Minnesota nurseries revealed the presence of P. hedraiandra de Cock & Man in't Veld and several other Phytophthora species but not P. ramorum. Symptomatic leaf and stem tissues from diseased Rhododendron and Quercus species were cultured on PARP, a selective growth medium for Phytophthora (3). The Phytophthora isolates obtained were later identified by sequencing the internal transcribed spacer (ITS) region of the rDNA and comparing the sequences with those in GenBank using BLAST searches (1). The ITS sequences of six cultures (GenBank Accession Nos. DQ139804-DQ139809), isolated during 2003 from various Rhododendron cultivars exhibiting leaf lesions and shoot dieback, showed 100% identity with the ITS sequence of P. hedraiandra (GenBank Accession No. AY707987) (2). This is a recently described pathogenic species from the Netherlands responsible for causing leaf spots on Viburnum spp. Since the ITS sequence of P. hedraiandra differs little from that of P. cactorum (2), we verified one isolate to be P. hedraiandra by sequencing the mitochondrial cytochrome c oxidase subunit I gene (cox1) (GenBank Accession No. DQ139810). Comparison of this sequence with the P. hedraiandra voucher specimen in GenBank (Accession No. AY769115) showed 99% identity, which was the closest match. Reproductive structures were measured on V8 juice agar. The average oogonium diameter for three isolates was 29 μm with a range of 26 to 32 μm, while the average antheridium length was 13 μm (11 to 15 μm). Sporangium length and width averages on crushed hemp seeds were 32 μm (28 to 36 μm) and 26 μm (21 to 30 μm), respectively, with the average length to width ratio of 1.25 (1.23 to 1.29). Pathogenicity tests on Rhododendron cv. Mikkeli were carried out using three of our P. hedraiandra isolates. Spore suspensions of 2 × 104 zoospores per ml were used to mist-spray shoots of five, 3-year-old plants for each isolate. Five controls were mist sprayed with water. After inoculation, plants were placed in plastic bags in a dark growth chamber (22°C) for 7 days and then moved to a greenhouse. Leaf blotches and shoot dieback were apparent 5 days after inoculation, and P. hedraiandra was reisolated from those symptomatic tissues and identified by an exact match of the ITS sequence. Necrotic areas lengthened from the shoot tips to the main stems of the plants while expanding into petioles and leaves. No symptoms were observed on control plants. To our knowledge, this is the first report of P. hedraiandra in the United States as well as the first report of Koch's postulates performed with P. hedraiandra on Rhododendron cv. Mikkeli. The significance of this disease to other woody plants in nurseries or the landscape is unknown, and further study is needed to determine the host range and extent of the disease that may occur from this introduction. References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) A. W. A.M de Cock and C. A. Lévesque. Stud Mycol 50:481, 2004. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

scholarly journals First Record of Phytophthora nicotianae Causing Leaf Blight on Rhododendron in Greece

Plant Disease ◽  
2011 ◽  
Vol 95 (6) ◽  
pp. 777-777
Author(s):  
P. Tsopelas ◽  
E. J. Paplomatas ◽  
S. E. Tjamos ◽  
K. Elena
Keyword(s):  
United States ◽  
Its Region ◽  
Maximum Growth ◽  
First Record ◽  
The United States ◽  
Culture Collection ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Phytophthora Nicotianae ◽  
Potted Plants

Species of Rhododendron and resulting hybrids are very important hosts of the quarantine pathogen Phytophthora ramorum, since they play a major role in the spread of the pathogen in Europe. However, many other Phytophthora species infect these hosts, causing similar symptoms. Widmer (4) listed 17 Phytophthora species as foliar pathogens of rhododendron in the United States. A survey was conducted in Greece in October 2009, in which potted plants of Rhododendron spp. were inspected for symptoms of necrotic lesions on leaves and buds caused by P. ramorum. Symptomatic plants were observed in one of the nurseries inspected in the Triphylia Region in southwestern Peloponnese. Isolations from symptomatic leaves on PARBhy-V8 selective agar medium (1) yielded Phytophthora isolates. Colonies on V8 juice agar appeared white and cottony, with a radial growth of 4.2 to 4.6 mm per day at 28°C with a maximum growth temperature of 36°C. Sporangia were produced abundantly on the medium surface and in water; the sporangia were broadly ovoid and papillate and 35 to 50 × 25 to 35 μm. Chlamydospores, 25 to 40 μm in diameter, were observed in 2-week-old cultures, while no sexual structures were observed. Three of the isolates examined were identified as P. nicotianae B. de Haan on the basis of morphological and physiological features (3,4). Genomic DNA was extracted from pure cultures of an isolate and the internal transcribed spacer (ITS) region was amplified using the ITS4/5 primer pair. Sequence analyses by BLAST indicated that the isolates were most similar to P. nicotianae (GenBank Accession No. AJ 854295.1) with sequence identity values of 99%. One of the isolates was deposited in the culture collection of the University of Athens (ATHUM 6519). Detached wounded leaves of Rhododendron hybrid cv. Red Jack were inoculated with agar plugs. Necrotic lesions, similar to those observed in the nursery, appeared on the inoculated leaves after 7 days of incubation at 26°C, while no symptoms developed on control leaves inoculated with sterile agar plugs. The pathogen was consistently reisolated from infected leaves, but not from the controls. P. nicotianae, being a thermophilic species, is the most common Phytophthora species in Greece, reported on more than 30 plant species (2). This pathogen has been reported on Rhododendron spp. in the United States (3,4), but to our knowledge, there was no record of this pathogen on these hosts as yet in Europe and this is the first published report of the pathogen on Rhododendron in Greece. References: (1) A. Belisario et al. Plant Dis. 87:101, 2003. (2) K. Elena. Technical Bulletin No 13. Benaki Phytopathological Institute. Athens, Greece (in Greek), 1999. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (4) T. L. Widmer. Online publication. doi: 10.1094/PHP-2010-0317-01-RS, Plant Health Progress, 2010.

scholarly journals First Report of Phytophthora ramorum on Rhododendron in Greece

Plant Disease ◽  
2011 ◽  
Vol 95 (2) ◽  
pp. 223-223 ◽  
Author(s):  
P. Tsopelas ◽  
E. J. Paplomatas ◽  
S. E. Tjamos ◽  
N. Soulioti ◽  
K. Elena
Keyword(s):  
Plant Species ◽  
Infected Plant ◽  
Weather Conditions ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Maximum Temperature ◽  
Width Ratio ◽  
Internal Transcribed Spacer Region ◽  
First Report ◽  
Adverse Weather

In April 2010, during a survey conducted in Fthiotis Prefecture of central Greece, symptoms of stem necrosis and leaf lesions were observed on two container-grown plants of Rhododendron, hybrid ‘Kate Waterer' in a nursery. From symptomatic leaves, a Phytophthora species was isolated on PARPH-V8 selective agar medium (2) with typical morphological characters of Phytophthora ramorum S. Werres & A.W.A.M. de Cock (4). The whole block of plants was under probation until molecular verification of the pathogen was completed. The nursery was reexamined 6 weeks after the first encounter, whereas spread of the pathogen was noticed to neighboring plants in the same block; five more Rhododendron plants with similar symptoms were recorded while one of the originally infected plants was dead. Isolates of Phytophthora with similar morphology were obtained from symptomatic leaves of three new plants as well as from the potting mix of a severely infected plant that was baited in a Rhododendron leaf assay (2). All Rhododendron plants in the block belonged to the same consignment imported from Belgium and covered by a phytosanitary plant passport. Colonies on 10% clarified V8 juice agar appeared with coralloid, coenocytic mycelium with radial growth at 1.7 mm per day at 20°C and maximum temperature 26 to 27°C. Propagules characteristic of P. ramorum, including semipapillate, caducous, sporangia measuring 35 to 55 × 15 to 30 μm (1.9 length/width ratio) and large chlamydospores (45 to 80 μm), were observed on V8 agar. One isolate was confirmed as P. ramorum by sequence analysis of the internal transcribed spacer region of rDNA and was deposited in the culture collection of the University of Athens (ATHUM 6522). Comparison of amplicon sequences (using ITS4/5 primer pair) of approximately 875 bp long was carried out using MEGABLAST search for highly similar sequences. Alignment data revealed the highest and most significant homology to P. ramorum (GenBank Accession No. AY594198.1) at 99%. Pathogenicity tests were carried out using detached leaves of Rhododendron hybrid ‘Red Jack’ and Arbutus unedo L., which were slightly wounded and inoculated with mycelium agar plugs (3). Necrotic lesions appeared on the inoculated leaves of both plant species 10 days after incubation at 20°C, while no symptoms developed on control leaves inoculated with sterile agar plugs. P. ramorum was consistently reisolated from artificially infected leaves of both plant species. Following confirmation of pathogen presence, eradication measures were applied in the nursery. The adverse weather conditions encountered in summer, with temperatures very often above 35°C, are expected to favor pathogen eradication. However, not all plants of the same consignment imported from Belgium were traced and it is possible that other infected plants have been sold in other areas of Greece. So far, P. ramorum had been reported in 21 other European countries; Serbia is the nearest country where the pathogen was detected (1). To our knowledge, this is the first report of P. ramorum in Greece. References: (1) A. Bulajić et al. Plant Dis. 94:703, 2010. (2) E. J. Fichtner et al. Phytopathology 97:1366, 2007. (3) R. G. Linderman et al Online publication. doi:10.1094/PHP-2007-0917-01-RS. Plant Health Progress, 2007. (4) S. Werres et al. Mycol. Res. 105:1155, 2001.

scholarly journals Diversity of Foliar Phytophthora Species on Rhododendron in Oregon Nurseries

Plant Disease ◽  
2015 ◽  
Vol 99 (10) ◽  
pp. 1326-1332 ◽  
Author(s):  
B. J. Knaus ◽  
V. J. Fieland ◽  
K. A. Graham ◽  
N. J. Grünwald
Keyword(s):  
Community Structure ◽  
Plant Pathogens ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Sudden Oak Death ◽  
Recent Emergence ◽  
Nursery Crops ◽  
The U.S

The genus Phytophthora contains some of the most notorious plant pathogens affecting nursery crops. Given the recent emergence of the sudden oak death pathogen Phytophthora ramorum, particularly in association with Rhododendron spp., characterization of Phytophthora communities associated with this host in nursery environments is prudent. Many taxa may present symptoms similar to P. ramorum but we do not necessarily know their identity, frequency, and importance. Here, we present a survey of Phytophthora taxa observed from seven nurseries in the U.S. state of Oregon. Incidence and diversity of Phytophthora communities differed significantly among nurseries and among seasons within nursery. The taxa P. syringae and P. plurivora were widespread and detected at most of the nurseries sampled. Nine other taxa were also detected but were found either in a single nursery or were shared among only a few nurseries. Characterization of the Phytophthora communities present in nurseries is an important step toward understanding the ecology of these organisms as well as an aid to nursery managers in determining what risks may be present when symptomatic plants are observed. This study builds on an increasing literature, which characterizes Phytophthora community structure in nurseries.

scholarly journals Susceptibility of Selected Ericaceous Ornamental Host Species to Phytophthora ramorum

Plant Disease ◽  
2004 ◽  
Vol 88 (9) ◽  
pp. 993-999 ◽  
Author(s):  
P. W. Tooley ◽  
K. L. Kyde ◽  
L. Englander
Keyword(s):  
Mating Type ◽  
Host Species ◽  
The United States ◽  
Phytophthora Ramorum ◽  
Natural Conditions ◽  
Experimental Conditions ◽  
Susceptible Host ◽  
Disease Symptoms ◽  
Kalmia Latifolia ◽  
Mountain Laurel

We assessed disease reactions of 51 species or varieties of ericaceous ornamental hosts to two isolates of Phytophthora ramorum, the causal agent of sudden oak death. Inoculation was performed with an A2 mating type U.S. isolate from rhododendron and the P. ramorum type culture of A1 mating type from Germany. For only one host were statistically significant differences in disease observed between the two isolates. Several different inoculation methods were compared. The 51 hosts tested varied widely in susceptibility, ranging from 0% to over 90% leaf area infected. Two cultivars of Vaccinium macrocarpon (cranberry) showed no disease, while three cultivars of Kalmia latifolia (mountain laurel) were all highly susceptible. The results indicate that many ornamental hosts grown in the United States are susceptible to P. ramorum under artificial inoculation conditions. Inoculum density studies with two susceptible host species showed that P. ramorum is capable of producing disease symptoms over sporangium concentrations ranging from 100 to 5,000 sporangia per ml. Mean numbers of chlamydospores forming in host tissue of 21 hosts ranged from 2 to over 900 chlamydospores per 6-mm-diameter leaf disk. Whether hosts showing susceptiblity under the experimental conditions used in this study would become infected with P. ramorum in the presence of inoculum under natural conditions is unknown.

scholarly journals First Detection of Phytophthora ramorum Mating Type A2 in Europe

Plant Disease ◽  
2003 ◽  
Vol 87 (10) ◽  
pp. 1266-1266 ◽  
Author(s):  
Sabine Werres ◽  
Daphné De Merlier
Keyword(s):  
United States ◽  
The Netherlands ◽  
Mating Type ◽  
The United States ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Taxus Baccata ◽  
Camellia Japonica ◽  
Wide Range

Since its original isolation in 1993, Phytophthora ramorum has become an important pathogen. Initially, it was determined to be the causal agent of a twig blight of Rhododendron spp. in Germany and the Netherlands (3). Around the same period, symptoms and mortality on oak (Quercus spp.) and tanoak (Lithocarpus densiflorus) were associated with P. ramorum in California (2), where the disease was named sudden oak death. Subsequently, P. ramorum has been detected on a wide range of forest trees and shrub species in the United States. In Europe, the pathogen has spread to many countries, primarily on nursery plants of Rhododendron and Viburnum spp., and recently, on Camellia japonica, Kalmia latifolia, Pieris formosa var. forrestii, P. japonica, Leucothoe sp., Syringa vulgaris, and Taxus baccata. P. ramorum has not been observed in European forests. P. ramorum is heterothallic, and initial in vitro mating studies on agar media suggested that only the A1 mating type occurred in Europe, while only the A2 mating type was present in the United States (4). However, an isolate collected in 2002 in Belgium (1) appears to be the A2 mating type. This isolate (CBS 110901, Centraal Bureau voor Schimmelcultures, Baarn, the Netherlands) originated from an imported V. bodnantense plant at an ornamental nursery. A hyphal tip culture (BBA 26/02) of this isolate produced no oogonia on carrot piece agar after 6 weeks in pairing tests with other Phytophthora species of mating type A2. When paired with mating type A1 of P. cambivora, P. cinnamomi, P. cryptogea, and P. drechsleri, however, oogonia were observed in all pairings within 6 weeks. The number of oogonia was low in all pairings but was highest in pairings with P. cryptogea. No oospores were produced after 6 weeks between P. ramorum isolates BBA 26/02 and BBA 9/95 (from the holotype, mating type A1), but gametangia were observed when these isolates were paired on Rhododendron sp. twigs. Normal oogonia were produced on the outgrowing mycelium when pieces from these twigs were placed on carrot piece agar. The shape and size of the oogonia produced on carrot piece agar after pairing with P. cryptogea and on Rhododendron sp. twigs after pairing with P. ramorum BBA 9/95 were similar (24 to 34 μm, mean 29.6 μm and 25 to 33 μm, mean 30.6 μm, respectively). To our knowledge, this is the first observation of P. ramorum mating type A2 in Europe. References: (1) D. De Merlier et al. Plant Dis. 87:203, 2003. (2) D. M. Rizzo et al. Plant Dis. 86:205, 2002. (3) S. Werres et al. Mycol. Res. 105:1166, 2001. (4) S. Werres and B. Zielke. J. Plant Dis. Prot. 110:129, 2003.

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