| DISTRIBUTION: Population structure of European and American lineages |
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The aims of this database are to collate the results of existing studies as well as from work carried
out in RAPRA WP 3 and WP 4, and summarise key characteristics and differences between the populations of P. ramorum |
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Work has been carried out on various aspects by research teams lead by the following:
- Professor Clive Brasier and co-workers (UK)*
- Dr Sabine Werres and co-workers (Germany)*
- Professor Matteo Garbelotto and co-workers (USA)
- Professor Kelly Ivors and co-workers (USA)
- Dr Peter Bonants and co-workers (The Netherlands)
- Dr Kurt Heungens and Prof. Ann Chandelier (Belgium)*
* Member of RAPRA consortium, others listed are not consortium members but are collaborators
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There are four main aspects that have been studied to address the population characterisation and identification issue. These are
- Morphological aspects including colony morphology (phenotypic stability)
- Sexual compatibility
- Molecular profiles of certain areas of the genome
- Continuous variables: Growth rate, pathogenic aggressiveness, host range
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Click to view summary table of adaptive differences between European and American lineages
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SUMMARY
P. ramorum was officially described in 2001 based on European isolates collected since 1993 from infected nursery ornamentals, particularly
rhododendrons and viburnums (Werres et al., 2001). It was realised in 2000 that the forest pathogen causing high mortality of native oaks in California
and parts of Oregon, USA in the late 1990s was the same organism as the EU pathogen (Brasier, Personal Communication; Rizzo et al., 2002).
Morphological (sporangial and chlamydospore characteristics) and genetic (AFLP, and microsatellite profiles) similarities among isolates from the two continents
confirmed conspecificity and elucidated three lineages (see below) (Kroon et al., 2004; Ivors et al., 2006).
Rapid diagnostic test to distinguish between American and European isolates of P. ramorum, Kroon et al., 2004
- 10871 KB;
Microsatellite markers, Ivors et al., 2006
-164 KB.
A new lineage was recently discovered based on differences in molecular polymorphisms (Ivors et al., 2006). Thus to date three lineages have been
identified, EU1, NA1 and NA2, the latter was found in nurseries in Washington State, USA (Ivors et al., 2006). Lineage EU1 is largely restricted to
Europe but has been reported from the USA (Hansen et al., 2003), where it was thought to have been imported on infected nursery stock from Europe.
All known infected material was destroyed in the USA to prevent further spread of this lineage on that continent. So far there have not been any reports
of lineage NA1 or NA2 from Europe.
The limited molecular variation evident in these different lineages suggests that they were introduced separately from a more variable original genepool
(Ivors et al., 2006).
P. ramorum is heterothallic (A1/A2) and therefore potentially outcrossing (Brasier et al., 2006). The separate lineages identified by adaptive
and genotypic differences are characterised by the predominance of different sexual compatibility types (Werres et al., 2001: Werres and Zielke, 2003;
Brasier et al., 2006; Werres and Kaminski, 2005). The USA lineages are exclusively A2 mating type while the EU lineage is predominated by the A1 mating
type with a single A2 isolated found in Belgium (Werres and De Merlier, 2003). Very recently (December 2006) Belgian researchers announced the discovery of 2
additional A2 EU lineage isolates in Belgium.
Differences in phenotypic stability and adaptive variation between European and American lineages of P. ramorum, Brasier et al., 2006
-5363 KB;
Characterisation of EU and NA isolates, Werres and Kaminski, 2005
-12210 KB.
In in vitro pairings between EU A1 and NA A2 isolates, oogonia were produced sparsely and unpredicatably and usually it took a long
time for oospores to form (Brasier and Kirk, 2004). It is thus unclear whether P. ramorum is actively outcrossing (Brasier et al., 2006).
Production of Gametangia, Brasier and Kirk, 2004
-324 KB
Phenotypic and adaptive differences (E.g. colony morphology and growth rate) are evident between isolates of P. ramorum collected from North America
compared with those from Europe (Brasier et al., 2006), and are summarised in Table 1. Isolates in the EU lineage uniformly display characteristic
'wild type' colony morphology
(Click
to view image) while the US lineage isolates are either typically wild type or are much slower growing and form non-wild type colonies demonstrating
an intrinsic instability
(Click
to view image Brasier et al., 2006). Differences between lineages
Pathogenicity tests carried out on bark of Quercus rubra (click to view image)
show significant differences in aggressiveness between two of the lineages (EU1 and NA1),
adding more evidence to adaptive differences between the different populations.
Differences between lineages
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REFERENCES
- Brasier CM, Kirk SA, Rose J, 2006. Adaptive differences between Phytophthora ramorum
isolates from Europe and North America: evidence for separate subspecies? Sudden Oak Death Science
Symposium, Monterey, California, January 2005 - Paper Abstract.
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- Brasier CM, Kirk SA, 2004. Production of gametangia by Phytophthora ramorum in vitro. Mycological Research
108, 823-827.
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- Hansen EM, Reeser PW, Sutton W, Winton LM, 2003. First report of A1 mating type of Phytophthora ramorum
in North America. Plant Disease 87 (10), 1267.
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- Ivors K, Garbelotto M, Vries IDE, Ruyter-Spira C, Te Hekkert B, Rosenzweig N, Bonants P, 2006.
Microsatellite markers identify three lineages of Phytophthora ramorum in US nurseries, yet single lineages in
UK forest and European nursery populations. Molecular Ecology 15, 1493-1505.
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- Kroon LPNM, Verstappen ECP, Kox LFF, Flier WG, Bonants PJM, 2004. A rapid diagnostic test to distinguish
between American and European populations of Phytophthora ramorum. The American Phytopathological
Society 94 (6) 613-620.
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- Rizzo DM, Garbelotto M, Davidson JM, Slaughter GW, Koike ST, 2002. Phytophthora ramorum as the cause of
extensive mortality of Quercus spp. and Lithocarpus densiflorus in California. Plant Disease 86, 205-14.
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- Werres S, Marwitz R, Man in't Veld WA, De Cock AWAM, Bonants PJM, De Weerdt M, Themann K, Ilieva E, Baayen RP, 2001.
Phytophthora ramorum sp. nov., a new pathogen on Rhododendron and Viburnum. Mycological Research 105
(10), 1155-1165. http://nature.berkeley.edu/comtf/pdf/Bibliography/werres2001a.pdf
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- Werres S, Zelke B, 2003. First studies on the pairing of Phytophthora ramorum.
Journal of Plant Disease and Protection 110, 129-130.
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- Werres S, Zelke B, 2003. First detection of Phytophthora ramorum mating type A2 in Europe. Plant Disease
87, 1266.
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- Werres S, Kaminski K, 2005. Characterisation of European and North American Phytophthora ramorum isolates due to their
morphology and mating behaviour in vitro with heterothallic Phytophthora species. Mycological Research 109 (8), 860-871.
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Contact for this Work Package: Sandra Denman at
Forest Research
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