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Phytophthora ramorum IN GALICIA (SPAIN)
ON Camellia, Rhododendron AND Viburnum
Phytophthora ramorum is a fungal pathogen included in the EPPO Alert List, being a potential risk for the EPPO region. In some areas of the United States it caused extensive death of Lithocarpus and Quercus sp, damaging also a wide range of ornamental species. This organism lives in mild to cold climates, with minimum temperatures of 2ºC, maximum ranging 26 - 30ºC and an optimum around 20ºC.
How does it spread? In short distance spread, this fungus can be disseminated by sporangia, the rain, irrigation water, wind and insects. Zoospores rapidly germinate on the leaf surface of the hosts, being them an important source of inoculum. In short distance spread, through infected plant material, vehicles, shoes, machines, etc. Fungus produces a large amount of chlamydospores that act as resistant structures.
What are its symptoms?
Depending on the species, symptoms can appear on the trunk surface, branches and/or leaves. In the American hosts, mainly on Lithocarpus densiflorus and Quercus spp, the most characteristic symptoms on adult trees are death of branches and the appearance of cankers on the bark of the trunk, with brownish spots and sap exudates. Lesions can extend from the tree collar up to 20 metres. Regarding leaf hosts, both American and European, symptoms vary, but in general they are associated to leaf spots and branch death.
Small twigs present a darkened brown colour. Sometimes these spots are surrounded by healthy tissue. Leaves present dark brown extensive spots, sometimes surrounded by almost unnoticeable concentric rings. In general, roots are not affected. Symptoms are similar to those caused by other Phytophthora species on Rhododendron, but this has a more rapid development.
Slight necrosis on leaves and peduncle. Infection can also start on the stalk base and rapidly progress and damage the whole plant.
There is little data on the symptoms observed in this culture, in fact so far there is only evidence of a single isolation of this pathogen in a Camellia japonica nursery in UK, and recently in California. Symptoms observed were mainly on the leaves which presented dark spots with diffuse margins, sometimes forming concentric rings; these spots can converge and affect the whole leaf, which may subsequently fall. Sometimes necrosis starts in the peduncle and progresses towards plant inside. Plants can also appear defoliated whereas roots remain healthy.
Where is it found?
In Europe it was not identified on oak yet, but it was found causing important damage on Rhododendron and Viburnum, in Holland, Germany, Belgium, Switzerland, Poland, France, Italy and United Kingdom, where it was also detected on Kalmia latifolia, Pieris spp and Camellia japonica, taking, in every case, the corresponding eradicative measures. In Spain, and more specially in Galicia, they were recently isolated and were present on Rhododendron spp, Viburnum timus and Camellia japonica.
What is being done in Galicia?
Galicia is an area adequate for the implantation and commercialization of acid plants, and since Phytophthora ramorum has a wide range of hosts and given that results of the fungus inoculation on camellia and eucalyptus showed that these plants had a high susceptibility to the fungus; Xunta de Galicia, through the Consellería de Política Agroalimentaria e Desenvolvemento Rural and the Estación Fitopatolóxica do Areeiro performed an exhaustive survey in the Galician nurseries, detecting Phytophthora ramorum on Viburnum timus, Rhododendron sp and Camellia japonica.
What should you do?
Phytophthora ramorum is a notifiable pathogen. If you suspect the presence of this disease on any of the plants above mentioned, you should immediately contact us.