Abstract
The oak-rangeland "dehesa" ecosystem plays an important economic, ecological and social role in south-westeern Europe. The decline of cork and holm oak trees and the absence of natural regeneration are the main concern of this valuable ecosystem. The decline syndrome can develop in a few months or several years and it has been explained by several concomitant factor of abiotic and biotic nature. Amon these factors, Phytophthora cinnamomi is considered the main cause of decline because its aggressive behaviour on the feeder roots of the oaks. However, its presence has not been always confirmed in the affected stands. To overcome traditional Phytophthora isolation difficulties, the aim of this work was to apply molecular methods to study Phytophthora diversity. Surveys were conducted in Extremadura region (wwestern of Spain) in five adult holm oak stands and thirteen regeneration zones. In each sampling sites, soil and root samples were collected from declining and non-declining holm oaks (Quercus ilex). The study compares t¡hree different approaches: 8i) traditional isolation methods consisting of roots in contact with selective media, and soil isolation using apples and leaf baits; (ii) 454-pyrosequencing analysis of root and soil samples with tagged amplicons specific for Phytophthora, and (iii) TaqMan real-time PCR of root and soil samples using P. cinnamomi specif probe.
