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Phytophthora austrocedri a pathogen that should not be underevaluated

There is a new, potential pest for many Cupressaceae, due to a Phytophthora species still little known. P. austrocedri (previously spelled as Phytophthora austrocedrae) was described in 2007 in Argentina as a cause of mortality of Ciprès de la cordillera (Austrocedrus chilensis (D. Don) Pic. Ser., and Bizzarri; synonyms: Cordillera Cypress; Chilean-incense Cedar, Mountain Cypress) in Patagonia. The pathogen was found in Great Britain in 2010 as an agent of decay in juniper (Juniperus communis) and in 2011 in a park in the North of England on Chamaecyparis lawsoniana and Chamaecyparis nootkatensis.

Reported in Germany in 2001 by the Julius Kuhn-Datasheet Institute on Juniperus horizontalis 'Glauca', is currently included (no. 21) in the list of 29 species of Phytophthora considered critical for the U.S., published by CPHST-Plant Epidemiology and Risk Analysis in 2009. Recently P. austrocedrae was included in the Cooperative Agricultural Pest Survey List (2014) and considered a priority in the programs of USDA regulations.

Studies on Phytophthora austrocedri have been conducted in Great Britain and Argentina, where the disease is widespread in nature on native tree and shrub species, respectively, Juniperus communis and Austrocedrus chilensis. On juniper symptoms consist in the appearance of widespread dieback of the foliage as a result of necrosis in the basal parts, originated in the root system and quickly extended along the trunk. Although with less frequency these necrosis were also described on the aerial parts.

Phloem tissues and the cambium undergo to an immediate destruction and loss of function. The cordillera cypress shows basal and root injuries in the first meter from the ground. Phloem, cambium change and first layers of the xylem are invaded by the hyphae of the pathogen.

The affected plants are heavily subject to uprooting because of fast processes of root rot by the numerous secondary organisms, promptly active after the death of vital tissues caused by P. austrocedri. The infection modality of this pathogen is far from being adequately known and shows, similarly to those of other more studied congeneric species, to have a very high complexity to rely on more than one infection strategy directed towards different host target tissues: branches, stem, crown, roots and probably thin roots.

Both in Europe and in Latin America the disease is more concentrated in sites with poor drainage and along watershed. Many species of Phytophthora share this ecological aspect, related to the aquatic dispersal of spores. Recent surveys of large areas in the province of Chubut have shown that the presence of wild pasture and roads are the most significant factors for the incidence of the disease.

The high virulence of P. austrocedri and the propensity towards the Cupressaceae family, fully justify the precautionary measures taken by the United States. The European Union, in this case in support of and in collaboration with the nursery sector, should shed more light on the issue, in order to stop any serious problems (actual and not just possible for the UK) both for potted plants trading and for the protection of natural areas at risk.

The fungus is considered critical for the USA. The potential risks for the family of cupressacee