Endophytic fungi in Quercus cerris : isolation frequency in relation to phenological phase, tree health and the organ affected

The isolation frequency of endophytic fungi in Quercus cerris was determined in relation to sampling data, the health state of the tree, and the tree organ affected. Sampling was carried out at three times, in April (budbreak), June (full vegetation) and October (leaf fall), on trees that were either healthy or in decline, and on three organs: current-year twigs, with a diameter less than 2 cm, buds, and leaves. The experiment was done in an approximately 20-year-old oak forest at an altitude of 350-400 m above sea level. Three healthy and three declining trees were sampled annually in 1999 and 2000. From each tree 20 current-year twigs, 20 buds and 10 leaves were harvested. Tissue fragments, after sterilization with 10% H2O2, were incubated on potato-dextrose-agar amended with streptomycin, at 20°C in the dark for 7 days, and the isolated mycelia maintained at 4°C on malt-extract agar. A total of 15 fungal species were isolated. All organs yielded fungal species but the greatest number of endophytic species came from current year twigs. Individual species were isolated more often from declining trees than from healthy trees, and more fungi were isolated in June (full vegetation) than in April or October. Diplodia mutila, Discula quercina and Phomopsis quercina, which are known to be pathogenetic on oaks, were present on oaks for a large part of the year. These fungi are both saprophytes (as endophytes) and parasites and are, therefore, probably a serious contributing and inciting factor in the oak decline syndrome