1. Phytophthora diversity in
UK gardens
Geoff Denton
Plant Pathologist
The Royal Horticultural Society

3. Detection Methods
Apple Baiting
Nested PCR
Immunoassay

4. Comparison of positive results from 2006 and 2007
from apple baiting, nested PCR and immunoassay
n
90 n =
= 380
144
80
Stem
70
n Root
= n Soil
60 320 =
Positive results (%)
92
50
40
30
n
n =
20 = n 401
145 =
413
10
0
Apple baiting Nested PCR Immunoassay

5. Positive results for the last 10 years from apple
baiting, nested PCR and immunoassay
Total tested
350
Positive apple baiting results
Positive nested PCR results
300 Positive immunoassay results
250
Number of Enquiries
200
150
100
50
0
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

6. Phytophthora species identified through
sequencing ITS
P. alni
P. cactorum
P. cambivora
P. cinnamomi P. cinnamomi
P. citricola P. citricola
P. citrophthora
P. cryptogea P. cryptogea
P. drechsleri
P. fragariae
P. gonapodyides
P. hibernalis
P. ideai
P. ilicis
P. inundata
P. megasperma
P. nicotianae
P. niederhauserii P. niederhauserii
P. pgchlamydo
P. porri
P. primulae
P. quercina
P. ramorum P. ramorum
P. sp.510
P. syringae
P. tropicalis/capsici P. tropicalis/capsici
0 20 40 60 80 100 120 140 160
Occurrence of species (n=489)

7. Phytophthora diversity
• In total 25 Phytophthora species have been
recorded in UK gardens
• During 2006 and 2007 alone we recorded 87
different host genera
• Top hosts are; Taxus (19%), Rhododendron
(5.6%), Rubus (4.2%) and Viburnum (4.2%)

8. Taxus Rubus Rhododendron Viburnum
P. cactorum - 1 - -
P. cinnamomi 32 - 2 2
P. citricola 20 9 4 2
P. citrophthora 6 - - -
P. cryptogea 7 2 2 -
P. fragariae - 3 - -
P. gonapodydies 3 - - 2
P. megasperma 1 - - -
P. nicotianae - - - 1
P. syringae 2 - - -
Phytophthora sp. - - - 1

9. Following the identification of the Phytophthora
species, potential new hosts for the following
species have been found:
• P. cactorum: Phylliopsis
• P. cambivora: Prunus laurocerasus
• P. citricola: Abutilon, Aesculus, Buddleja, Ceanothus, Convolvulus,
Cornus, Enkianthus, Fothergilla, Fremontodendron, Helleborus,
Lavendula, Pieris, Sorbus, Santolina, Symphoricarpus, Taxus,
Trachelospermum, Wisteria
• P. citrophthora: Ceanothus, Daphne, Heuchera
• P. cryptogea: Anemone, Araucaria, Calluna, Caryopteris, Choisya,
Cistus, Delphinum, Heliopsis, Heuchera, Prunus laurocerasus, Tilia,
Polemonium, Ribes, Rosmarinus, Ruta, Taxus, Thuja
• P. gonapodyides: Rubus, Sorbus, Taxus
• P. hibernalis: Hebe
• P. megasperma: Hedera

10. Proportion of Pythium and Phytophthora
identified by sequencing of ITS region, through
all detection methods
300
Pythium
250
Phytophthora & Pythium
38%
Phytophthora
Number of Enquiries
200
5%
150
100
57%
50
30%
9%
61%
0
2006 2007
Year

11. Comparison of total Phytophthora and
Pythium identified, by method and sample
250
Pythium
Phytophthora
200
Number of Enquiries
150
100
50
0
Stem (PCR) Roots (PCR) Soil (PCR) Stem (Bait) Roots (Bait) Soil (Bait)

12. Pythium species identified through
sequencing ITS
Py attrantheridium Py attrantheridium
Py chamaehyphon
Py heterothallicum
Py helicoides
Py intermedium Py intermedium
Py irregulare
Py macrosporum
Py minus
Py monospermum
Py montanum
Py oligandrum
Py parvum
Pythium sp.
Py sylvaticum Py sylvaticum
Py ultimum
Py vanterpoolii
Py vexans
Py violae
0 5 10 15 20 25 30 35 40 45
Occurrence of species (n=160)

13. Pythium diversity
• In total 17 Pythium species have been recorded
in UK gardens
• During 2006 and 2007 alone we recorded 72
different host genera
• Top hosts are; Taxus (12.6%), Prunus (4.9%),
Rubus (4.2%) and Cornus (3.5%)

14. Taxus Prunus Rubus Cornus
Py attrantheridium 3 1 2 2
Py heterothallicum 2 1 2 -
Py intermedium 2 3 1 -
Py irregulare 1 - - -
Py macrosporum 1 - - -
Py monospernum 1 - - -
Py montanum 1 - - -
Py oligandrum - - 1 -
Py sylvaticum 3 1 - 2
Py vexans - - - 1
Pythium sp. 7 4 - -