Influence of site factors on the impact of Phytophthora cinnamomi in cork oak stands in Portugal

• Published in: Forest pathology = Journal de pathologie forestière = Zeitschrift für Forstpathologie 2005-06, Vol.35 (3), p.145-162
• Main Authors: Moreira, A.C, Martins, J.M.S
• Format: Article
• Language: English
• Subjects: alternative hosts; aspect; Cistaceae; disease prevalence; Ericaceae; forest trees; fungal diseases of plants; geographical variation; Phytophthora cinnamomi; plant pathogenic fungi; Quercus; Quercus ilex subsp. rotundifolia; Quercus suber; rhizosphere; risk factors; roots; shrubs; spatial variation; topography; tree diseases; tree mortality; understory
• ISSN: 1437-4781; 1439-0329
• DOI: 10.1111/j.1439-0329.2005.00397.x

Summary 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 of Phytophthora cinnamomi in 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 with P. cinnamomi, which was detected mainly on species belonging to the families Ericaceae, Cistaceae and Leguminosae. Recovery of P. cinnamomi was 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 of P. 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 of P. cinnamomi in roots and rhizosphere. Different morphotypes of P. cinnamomi could be distinguished in 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. Résumé Le dépérissement des chênes verts et chênes liège, décrit au Portugal depuis la fin du XIXème siècle, est devenu très préoccupant au cours des deux dernières décennies. La présence de Phytophthora cinnamomi dans les peuplements de chênes verts et chênes liège a étéétudiée dans 4 régions du Portugal (Trás‐os‐Montes, Alentejo, Ribatejo et Algarve) pendant la période 1995–98. La sévérité du dépérissement, les mortalités brutales et les caractéristiques stationnelles ont été relevées dans 56 sites représentant des conditions variées. Le pathogène a été isoléà partir d’échantillons de racines de chênes ou de la rhizosphère dans 27 de ces sites. D'autres espèces de plantes d