''Phytophthora lateralis'' is a soil-borne

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

that causes cedar root disease in Lawson cypresses (''

Chamaecyparis lawsoniana ''Chamaecyparis lawsoniana'', known as Port Orford cedar or Lawson cypress, is a species of conifer in the genus ''Chamaecyparis'', family Cupressaceae. It is native to Oregon and northwestern California, and grows from sea level up to in the v ...

'') in Northern

USA The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. This pathogen was first noted to cause disease in around 1920 on nursery stock near

Seattle Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest regio ...

.Tucker, C.M.; Milbrath, J.A., 1942: Root rot of ''Chamaecyparis'' caused by a species of ''Phytophthora''. Mycologia 34, 94–101. Pacific yew (''

Taxus brevifolia ''Taxus brevifolia'', the Pacific yew or western yew, is a species of tree in the yew family Taxaceae native to the Pacific Northwest of North America. It is a small evergreen conifer, thriving in moisture and otherwise tending to take the form o ...

'') is also vulnerable to ''P. lateralis'' but less susceptible than Lawson cypress trees, and tree mortality has only been observed in areas where ''C. lawsoniana'' trees were also infected. Asiatic species of ''

Chamaecyparis ''Chamaecyparis'', common names cypress or false cypress (to distinguish it from related cypresses), is a genus of conifers in the cypress family Cupressaceae, native to eastern Asia (Japan and Taiwan) and to the western and eastern margins of th ...

'' are generally described as resistant to ''P. lateralis'', although this pathogen is occasionally isolated from ''

Chamaecyparis obtusa ''Chamaecyparis obtusa'' (Japanese cypress, hinoki cypress or hinoki; ja, 檜 or , ) is a species of cypress native to central Japan in East Asia, and widely cultivated in the temperate northern hemisphere for its high-quality timber and orna ...

'' (Hinoki cypress) in nurseries.

Mode of infection

The most frequent symptoms of disease caused by ''P. lateralis'' are root and collar lesions. Trees become infected by their roots coming into contact with the

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s in the soil or water.

Hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e then develop in larger roots and into the root collar where they kill the inner bark. Infrequent foliar infections resulting in branch lesions, have also been reported.Robin, C., Piou, D., Feau, N., Douzon, G., Schenck, N., Hansen, E.M. 2010. Root and aerial infections of ''Chamaecyparis lawsoniana'' by ''Phytophthora lateralis'': a new threat for European countries. Forest Pathology,

Symptoms

The foliage of infected trees initially appears slightly lighter in colour than that of healthy trees. The whole

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

turns then to pale green, yellow and then light-brown when the tree is dying. As the pathogen extends from the roots and root collar up the trunks, a sharp margin is visible between necrotic

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

, discoloured to cinnamon brown and healthy cortical tissues.

Distribution

Until recently, the known distribution area of ''P. lateralis'' was limited to

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Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

, and

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

where it mostly occurs. In 2009, the pathogen was detected in soil of natural forests of ''C. obtusa'' in Taiwan, in agreement with a possible Asiatic origin for this species. Recent outbreaks have been recorded on ''C. lawsoniana'' in

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

, and the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

Possible risks

Since ''C. lawsoniana'' and ''T. brevifolia'' are both key components of ecosystems on the Pacific Northwest Region of North-America, ''P. lateralis'' is threatening the ecological and economical values of forests where the pathogen occurs. In Europe, where ''C. lawsoniana'' is a widespread ornamental tree, ''P. lateralis'' could represent a serious threat, especially for the ornamental plant industry if it becomes established. Because of its potential economic impact, this pathogen was added in 2006 to the A1 list of exotic species that the EPPO recommends to regulate as quarantine organisms. It was transferred to the A2 list in 2011 as it was then considered established in some EPPO countries.

References

External links

Index Fungorum

USDA ARS Fungal Database

{{Taxonbar, from=Q7189824 lateralis Water mould plant pathogens and diseases Conifer pathogens and diseases