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Concept
Phytophthora ramorum
Résumé
Phytophthora ramorum is the oomycete (a type of protist) plant pathogen known to cause the disease sudden oak death (SOD). The disease kills oak and other species of trees and has had devastating effects on the oak populations in California and Oregon, as well as being present in Europe. Symptoms include bleeding cankers on the tree's trunk and dieback of the foliage, in many cases leading to the death of the tree.
P. ramorum also infects a great number of other plant species, significantly woody ornamentals such as Rhododendron, Viburnum, and Pieris, causing foliar symptoms known as ramorum dieback or ramorum blight. Such plants can act as a source of inoculum for new infections, with the pathogen producing spores that can be transmitted by rainsplash and rainwater.
P. ramorum was first reported in 1995, and the origins of the pathogen are still unclear, but most evidence suggests it was introduced as an exotic species to Europe and North America in separate events. Very few control mechanisms exist for the disease, and they rely upon early detection and proper disposal of infected plant material.
The disease is known to exist in California's coastal region between Big Sur (in Monterey County) and southern Humboldt County. It is confirmed to exist in all coastal counties in this range, as well as in all immediately inland counties from Santa Clara County north to Lake County. It has not been found east of the California Coast Ranges, however. It was reported in Curry County, Oregon, just north of the California stateline, in 2001. Sonoma County has been hit hardest, having more than twice the area of new mortality of any other county in California.
About the same time, a similar disease in continental Europe and the UK was also identified as Phytophthora ramorum.
It was first discovered in California in 1995 when large numbers of tanoaks (Notholithocarpus densiflorus) died mysteriously, and was described as a new species of Phytophthora in 2000. It has subsequently been found in many other areas, including some other U.
Source officielle
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