Phytophthora lateralis: addition to the EPPO Alert List
A disease killing Chamaecyparis lawsoniana (Port-Orford-cedar or Lawson’s cypress) grown for ornamental purposes in nurseries was first noted in 1923, in Seattle, Washington (US). The pathogen was identified in 1942 as Phytophthora lateralis. In the 1950s, the disease started to spread in the forests within the natural range of C. lawsoniana in northwest California and southwest Oregon. The disease has also been reported from British Columbia in Canada. In Europe, P. lateralis was isolated from C. lawsoniana on two occasions (in 1996 and in 1998) in different parts of France, but it was felt that these findings were related to a single original infestation of young, potted, greenhouse-propagated trees in a commercial nursery (probably resulting from an introduction from North America). It is felt that P. lateralis has been introduced into North America, but so far its origin could not be traced as the disease is not known elsewhere in the world. In 1991, P. lateralis was also reported from Taxus brevifolia which appeared as a less susceptible host. Tree mortality of T. brevifolia was only observed in areas where they were growing along streams in close association with dead or dying C. lawsoniana. P. lateralis causes a root rot. It infects the roots which appear water soaked with a red-brown discoloration. Roots are killed as the disease progresses. A red-brown necrotic lesion of the inner bark extends to the basis of the trunk (50 cm or more above ground). Foliage of the affected trees gradually changes in colour from yellow to bronze and finally to light brown and it becomes crisp and dry. Infected trees are often attacked by Phloeosinus bark beetles. C. lawsoniana seedlings are killed within a few weeks and large trees die within 2 to 4 years. The disease is favoured by wet and cool conditions (optimum temperature between 15 and 20 °C). P. lateralis survives the hot and dry summers as chlamydospores in the soil or decomposed roots. It is noted that in areas where temperatures are moderately high and conditions are moist, root rot of C. lawsoniana is usually caused by P. cinnamomi (e.g. in southern USA and Europe). P. lateralis can be disseminated through root contact, zoospores in water, and resting spores (chlamydospores) in infected soil. In forests, the disease is essentially disseminated through water streams and contaminated soil (on boots, vehicules, machinery etc.). In particular, it is spread through earth movement in road construction, maintenance and use, and logging operations. Management programmes include closing of roads, destruction of C. lawsoniana growing as ‘weeds’ along the roads, disinfection of boots, vehicles and machinery. Studies on the use of tolerant or resistant cultivars are also being carried out. It is felt that this disease has caused dramatic ecological and economic losses. C. lawsoniana is considered as an extremely valuable timber wood and is widely used for ornamental purposes. In some localities in northwest Oregon and western Washington, the disease was so severe that nurseries could no longer produce C. lawsoniana. In gardens and parks, it continues to kill hedgerows and landscape trees. In natural forests, well-established C. lawsoniana plantations have been devastated and others are still at risk. In Europe, C. lawsoniana is occasionally planted in forests but is a widespread ornamental tree, and P. lateralis could represent a serious threat for the ornamental plant industry if introduced.
Phytophthora lateralis: a severe root rot disease of Chamaecyparis lawsoniana
Why: Phytophthora lateralis came to our attention during a bibliographic search on sudden oak disease (caused by another Phytophthora species), as significant tree mortality and severe losses are reported in USA on C. lawsoniana growing in nurseries, gardens and forests.
Where: North America: Canada (British Columbia), USA (California, Oregon, Washington).
On which plants: Chamaecyparis lawsoniana. Taxus brevifolia has also been reported as a host plant but it is less susceptible and tree mortality has only been observed in areas where C. lawsoniana trees were also infected.
Damage: Root rot leading to tree mortality.
Transmission: Root contact, zoospores in water, resting spores (chlamydospores) in the soil.
Pathway: Plants for planting and wood of host plants (C. lawsoniana, Taxus brevifolia), infested soil from areas where P. lateralis occurs.
Possible risks: In the EPPO region, C. lawsoniana is occasionally planted in forests but is a widespread ornamental tree. P. lateralis causes tree mortality in all cases and there is no curative treatment available. It could represent a serious threat, especially for the ornamental plant industry if introduced into the EPPO region. The isolated finding in France also suggests that there is a pathway for introducing the pathogen (may be through contaminated soil attached to C. lawsoniana or other non-host plants).
EPPO RS 2001/034
Panel review date 2001- Entry date 2001-02
Sources
Hansen, E.M.; Goheen, D.J.; Jules, E.S.; Ullian, B. (2000) Managing Port-Orford-Cedar and the introduced pathogen Phytophthora lateralis.
Hansen, E.M.; Streito, J.C.; Delatour, C. (1999) First confirmation of Phytophthora lateralis in Europe. Plant Disease, 83(6), p 587.
Murray, M.S.; Hansen, E.M. (1997) Susceptibility of Pacific Yew to Phytophthora lateralis. Plant Disease, 81(12), 1400-1404.
DeNitto, G.A.; Kliejunas, J.T. (1991) First report of Phytophthora lateralis on Pacific yew. Plant Disease, 75(9), p 968.
Erwin, D.C. Ribeiro, O.K (1996) Phytophthora lateralis. In: Phytophthora diseases worldwide. American Phytopathological Society, St. Paul (US), pp 365-367. Plant Disease, 84(1), 4-14.
INTERNET
USDA. Forest Service. Pacific Northwest Region. Ecology and management of Port-Orford-cedar. http://www.fs.fed.us/r6/siskiyou/poc1.htm
USDA. Forest Service. Pacific Northwest Region. Port-Orford-Cedar root disease by Roth, L.W.; Harvey Jr, R.D;; Kliejunas, J.T. http:// http://www.fs.fed.us/r6/nr/fid/fidls/poc.html