Abstract
The population of European ash (Fraxinus excelsior) in Europe is severely affected by ash dieback disease caused by Hymenoscyphus fraxineus. Endophytic fungi are known to influence tree fitness and there are efforts to use them directly or indirectly in the biological control of tree pathogens.
To assess possible variation in the fungal community depending on the health status of the tree, three pairs of ash dieback relatively resistant and ash dieback susceptible adult trees were selected from two locations. The diversity of fungal endophytes in healthy ash shoots was investigated in the summer and winter season by agar culture isolations.
To screen for the antagonistic potential of ash endophytes to H. fraxineus, 48 isolated taxa were tested in dual cultures with the pathogen. Distinctive seasonal changes were observed in the identified fungal communities.
Endophytes with a presumptive saprotrophic functional role increased in the summer, whereas presumptive pathogenic taxa increased in winter. Furthermore, species diversity was significantly higher in the winter.
Higher frequencies of Diaporthe sp. 1 and Diaporthe sp. 2 were recorded in susceptible trees than in resistant trees. However, no significant differences were found between community structures.
The growth of H. fraxineus was significantly reduced by 36 endophytes, with inhibition rates ranging from 42 to 83%. The best inhibition results were obtained for fast growing fungi such as Botrytis cinerea and Phoma macrostoma var. incolorata.