''Phytophthora lateralis'' is a soil-borne

plant pathogen Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like orga ...

that causes cedar root disease in Port Orford cedars ('' Chamaecyparis lawsoniana''). This pathogen was first noted to cause disease in around 1920 on nursery stock near

Seattle Seattle ( ) is the most populous city in the U.S. state of Washington and in the Pacific Northwest region of North America. With a population of 780,995 in 2024, it is the 18th-most populous city in the United States. The city is the cou ...

.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'') 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'' 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; or , ) is a species of cypress native to central Japan in East Asia, and widely cultivated in the temperate climate, temperate northern hemisphere for its high-quality timber ...

'' (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 in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...

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 o ...

e then develop in larger roots and into the root collar where they kill the inner

bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

. 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 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 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 transport process is ...

, discoloured to cinnamon brown and healthy cortical tissues.

Distribution

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

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, and

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

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

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Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...

, and the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

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

{{Authority control lateralis Water mould plant pathogens and diseases Conifer pathogens and diseases