Spatio-temporal analysis of Phytophthora ramorum cases in England and Wales, spatially-explicit simulations, plant trade network, epidemic threshold. Evolution of the international regulation of plant pests andchallenges for future plant health. Plant health and global change – some implications for landscape management

1. Epidemiological modelling of Phytophthora
ramorum incidence and spread in the UK
Tom Harwood, Marco Pautasso*, Xiangming Xu,
Mike W. Shaw & Mike J. Jeger*
*Division of Biology, Imperial College London,
Silwood Park Campus, SL5 7PY, UK
International Congress of Plant Pathology nr 10,
Torino (Italy) August 2008

2. Phytophthora ramorum in England & Wales (2003-2006)
511 nurseries/ 168 historic gardens/
garden centres woodlands 122
85
46
426
Climatic match courtesy of Outbreak maps courtesy of
Richard Baker, CSL, UK David Slawson, PHSI, DEFRA, UK

3. Spatial analysis – aggregation
of nurseries & garden centres
a: G arden/N ursery 2003 b: G arden/N ursery 2004
5 5
4 4
3 3
g11 values
2 2
1 1
0 0
c: G arden/N ursery 2005 d: G arden/N ursery 2006
5 12
4
8
3
g11 values
g11 values
2
4
1
0 0
0 20 40 60 80 100 0 20 40 60 80 100
D istance (km ) D istance (km )

4. Simulations
Log (total numbers of infected plants after 10 years)
Source of variation df MS VR P
Between locations 9 1774 694 <0.001
Allowing for differences between locations
R 1 18270 7147 <0.001
commerce 1 2087 817 <0.001
inspections 1 49 19 <0.001
R.commerce 1 126 49 <0.001
Other interactions very small and non-significant
Residual 3983 2.56

5. Lower epidemic threshold for two-way scale-free networks
(unless networks are sparsely connected)
N replicates = 100;
error bars are St. Dev.;
different letters show
sign. different means
at p < 0.05

6. References
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industry: some implications for plant health. Scientia Horticulturae 125: 1-15
Harwood TD, Xu XM, Pautasso M, Jeger MJ & Shaw M (2009) Epidemiological risk assessment using linked network
and grid based modelling: Phytophthora ramorum and P. kernoviae in the UK. Ecological Modelling 220: 3353-3361
Jeger MJ & Pautasso M (2008) Comparative epidemiology of zoosporic plant pathogens. European Journal of Plant
Pathology 122: 111-126
MacLeod A, Pautasso M, Jeger MJ & Haines-Young R (2010) Evolution of the international regulation of plant pests and
challenges for future plant health. Food Security 2: 49-70
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threshold, correlation between links to and from nodes, and clustering. Journal of Theoretical Biology 260: 402-411
Moslonka-Lefebvre M, Finley A, Dorigatti I, Dehnen-Schmutz K, Harwood T, Jeger MJ, Xu XM, Holdenrieder O &
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Plant health and global change – some implications for landscape management. Biological Reviews 85: 729-755
Pautasso M, Moslonka-Lefebvre M & Jeger MJ (2010) The number of links to and from the starting node as a predictor
of epidemic size in small-size directed networks. Ecological Complexity 7: 424-432
Pautasso M, Xu XM, Jeger MJ, Harwood T, Moslonka-Lefebvre M & Pellis L (2010) Disease spread in small-size
directed trade networks: the role of hierarchical categories. Journal of Applied Ecology 47: 1300-1309
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(Phytophthora ramorum) in England and Wales. Ecography 32: 504-516