| Abstrakt: |
Although decline of cork (Quercus suber) and holm oak trees (Quercus rotundifolia) has been described in Portugal in the late years of the 19th century, its development has become a motive of high concern during the last two decades. The presence ofPhytophthora cinnamomiin cork and holm oak stands was surveyed in four different regions of the country (Trás-os-Montes, Alentejo, Ribatejo and Algarve) during 1995–98. Tree decline severity, sudden death and site characteristics were assessed in 56 sites representing varied conditions. The pathogen was isolated from oak roots and rhizosphere samples in 27 of those places. Other plant species from natural vegetation were sampled in three active disease centres. This survey showed that 56% of the surveyed species of shrub flora were infected withP. cinnamomi, which was detected mainly on species belonging to the familiesEricaceae,CistaceaeandLeguminosae. Recovery ofP. cinnamomiwas more frequent in shallow soils (Leptosols and complex Leptosols and Luvisols). These soils are more common in the south (Algarve), where decline has a high impact. Soils with low fertility and low mineral nutrient levels, particularly phosphorus, seemed to favour infection. Site aspect and topographic tree situation were also evaluated. Sites facing south showed higher occurrence ofP. cinnamomi, which was also more frequent in slopes and valleys than on hilltops. In Algarve, a relationship could be established between the crown status and the presence ofP. cinnamomiin roots and rhizosphere. Different morphotypes ofP. cinnamomicould be distinguishedin vitro, and their occurrence in the field was correlated with particular site characteristics. Further research needs and management strategies to limit the extension of the disease are discussed. [ABSTRACT FROM AUTHOR] |
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