Changes in Ectomycorrhizal Diversity in a Declining Quercus ilex Coastal Forest

Oak decline is generally accepted to be the result of a dynamic interaction between oaks and a mix of abiotic and biotic causes, within which environmental stresses (drought, salinity, frost, low fertility) may be important as predisposing factors. As a result of these interactions, trees gradually begin to show symptoms of general suffering, which below ground consist of functional and anatomical modifications to the rootlets and changes in the ectomycorrhizal status. The present study was performed in a coastal Quercus ilex forest, where decline symptoms appeared after heavy land reclamation in the adjoining areas, which caused a rapid lowering of the ground water level and the underground intrusion of seawater from the neighbouring Adriatic Sea into the forest itself. A forest survey including examination of rootlet features from asymptomatic and declining trees suggested that drought and salinity were involved in this decline. The relative frequency of the most recurrent ectomycorrhizal morphotypes distinguished clearly between asymptomatic, weakly declining and strongly declining trees, suggesting that the occurrence and distribution of only a limited number of morphotypes can give an indication of the severity of the decline. Moreover, of all the morphotypes observed only one third were found in all three decline classes, while the remaining two thirds were gradually replaced by others as the proportion of declining trees increased, where the number of morphotypes was greater. The hypothesis of an adaptive response of the ectomycorrhizal community to decline or to the predisposing factors of decline is discussed

Hygrotermic Treatment of Chesnut Logs Infected with Cryphonectria parasitica

Due to the reduced availability of large-sized chestnut logs in Europe, many European timber industries currently get their supplies from non-European countries, mainly from the Caucasian region, which are often not immune to chestnut blight. Given the high risk of introducing new virulent strains incompatible with local hypovirulent ones, the European Union regulation requires that chestnut logs, imported from so-called “third party” nations where Cryphonectria parasitica is present, reach the European boundaries bark free: this prevents the production of veneers, which are highly remunerative, but whose first workmanship phases require barked logs. Following a multilevel investigation, the authors propose a stem-flow protocol that can devitalise the parasite in barked logs while preserving the commodity characteristics of the wood, through a fast, simple and low-cost treatment, that can be performed at the European borders whenever C. parasitica is or might be present

Probability of ectomycorrhizal infection in a declining stand of common oak

The study was conducted on 50-55-year-old common oak (Quercus robur L) trees growing in a Ornithogalo pyrenaici-Carpinetum betuli. Four different classes of decline were determined. In each class, in a root sample belonging to ten common oaks, the number of tips with and without mycorrhizal mantle were counted and the probability of finding vital mycorrhizae was determined. The mycorrhizal morphotypes were described and their frequency calculated. The study demonstrated a significant decrease in the proportion of mycorrhizae between healthy and declining plants. Among damaged trees, the increase in decline did not correspond to a decrease in the probability of mycorrhizal infection. There was no correspondance between the probability of finding vital mycorrhizae and decline intensity. Most mycorrhizal morphotypes were found to be distributed homogeneously in the different classes of decline. Some of them, however, can be associated with the degree of decline in a variable manner. Relationships between growth anomalies and mycorrhizal infection are also discussed.Probabilité d'ectomycorhization du chêne pédonculé dans une forêt dépérissante. L'étude a été menée sur des chênes âgés de 50-55 ans croissant dans un Ornithogalo pyrenaici-Carpinetum betuli. Quatre classes de dépérissement des arbres ont été déterminées dont la première comportait uniquement des arbres sains. Pour chaque classe, les apex racinaires mycorhizés et non mycorhizés ont été dénombrés dans des échantillons de racines prélevées à partir de dix arbres et la probabilité de trouver des mycorhizes vivantes a été déterminée. Les morphotypes de mycorhizes ont été séparés et décrits et leur fréquence a été calculée pour chaque classe de dépérissement. L'étude a démontré que la probabilité qu'un apex racinaire soit mycorhizé est significativement plus élevée pour les arbres sains que pour les arbres dépérissants. En revanche, parmi ces derniers, on n'a pas relevé de correspondance entre la probabilité de trouver des mycorhizes viables et la sévérité du dommage. La plupart des morphotypes sont distribués de façon homogène parmi les différentes classes de dépérissement. Toutefois, quelques morphotypes semblent être associés de façon variable avec la sévérité du dépérissement. Les relations entre les anomalies de croissance et la mycorhization sont discutées

The mycorrhizal status of a declining stand of Quercus robur

Nanc

Vegetative compatibility and conversion to hypovirulence among italian isolates of Cryphonectria parasitica

pubblicato in Phytoparasitica 1994, 22/2: 17

Superamento dell'incompatibilit\ue0 vegetativa in Cryphonectria parasitica

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