Combining Inferential and Deductive Approaches to Estimate the Potential Geographical Range of the Invasive Plant Pathogen, Phytophthora ramorum
Phytophthora ramorum. PLoS ONE 8(5): e63508. doi:10.1371/journal.pone.0063508
Combining Inferential and Deductive Approaches to Estimate the Potential Geographical Range of the Invasive Plant Pathogen, Phytophthora ramorum
Kylie B. Ireland 0
Giles E. St. J. Hardy 0
Darren J. Kriticos 0
Zhengguang Zhang, Nanjing Agricultural University, China
0 1 Cooperative Research Centre for National Plant Biosecurity, Canberra, Australian Capital Territory, Australia, 2 Centre for Phytophthora Science and Management, School of Veterinary and Life Sciences, Murdoch University , Perth, Western Australia , Australia , 3 Commonwealth Scientific and Industrial Research Organisation (CSIRO) Ecosystem Sciences, Canberra, Australian Capital Territory , Australia
Phytophthora ramorum, an invasive plant pathogen of unknown origin, causes considerable and widespread damage in plant industries and natural ecosystems of the USA and Europe. Estimating the potential geographical range of P. ramorum has been complicated by a lack of biological and geographical data with which to calibrate climatic models. Previous attempts to do so, using either invaded range data or surrogate species approaches, have delivered varying results. A simulation model was developed using CLIMEX to estimate the global climate suitability patterns for establishment of P. ramorum. Growth requirements and stress response parameters were derived from ecophysiological laboratory observations and site-level transmission and disease factors related to climate data in the field. Geographical distribution data from the USA (California and Oregon) and Norway were reserved from model-fitting and used to validate the models. The model suggests that the invasion of P. ramorum in both North America and Europe is still in its infancy and that it is presently occupying a small fraction of its potential range. Phytophthora ramorum appears to be climatically suited to large areas of Africa, Australasia and South America, where it could cause biodiversity and economic losses in plant industries and natural ecosystems with susceptible hosts if introduced.
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Funding: The authors would like to acknowledge the support of the Australian Governments Cooperative Research Centres Program and the Cooperative
Research Centre for National Plant Biosecurity in particular. We also acknowledge the financial support of the Australian Government Department of
Sustainability, Environment, Water, Population and Communities and the School of Biological Sciences at Murdoch University. The funders had no role in study
design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Phytophthora ramorum is an invasive plant pathogen causing
considerable and widespread damage in nurseries, gardens,
natural woodland and plantation forest ecosystems of the USA
and Europe [1,2]. It is internationally recognized as a plant
biosecurity threat in many regions. Australia, Canada, the Czech
Republic, Mexico, New Zealand, South Korea and Taiwan have
established specific quarantine policies and protocols to prevent
the spread of contaminated plant materials from areas known to
have the disease [3]. Outbreaks of the pathogen into areas of the
west coast of the USA containing remnant native vegetation,
particularly in central coastal California, have decimated
populations of the keystone species tanoak (Notholithocarpus densiflorus) and
coast live oak (Quercus agrifolia) [4,5]. Similarly in England, P.
ramorum has caused mortality of important ecological and
commercial species such as Vaccinium myrtillus in heathlands [6]
and Japanese larch (Larix kaempferi) in plantations [2]. While
eradication efforts have been undertaken in natural areas of
Oregon, USA [7] and parts of Europe [8], P. ramorum continues to
invade new forest sites in these regions and in coastal California
where eradication efforts have not been attempted.
While the geographical centre of origin for P. ramorum remains
unknown, both molecular and biological evidence suggest that it is
exotic to both North America and Europe. Phytophthora ramorum
populations in Europe and North America are dominated by
different mating types [9] and significant genotypic and
phenotypic differences exist between these populations [10,11,12,13]. At
present, four distinct clonal lineages (NA1, NA2, EU1 and EU2)
have been identified from North America and Europe [11,14].
NA1, NA2 and EU1 are all found in North American nurseries,
while NA1 is the only genotype present in Californian and Oregon
forests [11]. In Europe, EU1 is the dominant genotype in nurseries
and forests, while EU2 is a newly discovered genotype only known
at present from infected L. kaempferi in Northern Ireland and
Southern Scotland [14]. Although the disease emerged around the
same time in nurseries in Europe and woodlands in California (the
early to mid-1990s), molecular evidence (...truncated)