1. The role of competitive interactions among endophytes and latent pathogens that determine disease on stressed plants is largely unknown. 2. Shoot blight caused by Diplodia sapinea is an emerging disease affecting pine forests in Europe. D. sapinea is an endophyte that becomes pathogenic following drought or hail. Disease expression depends on the availability of nutrient-rich metabolites produced by trees to alleviate stress. We studied whether competition for these compounds with other endophytes could modulate symptom expression. 3. We compared the shoot-inhabiting fungal community of trees that developed blight symptoms or remained asymptomatic following a hailstorm that affected four pine species. Communities were characterised by isolation and metabarcoding of the ITS2 region. Endophytes were functionally annotated in their response to C, N and proline. 4. Hail promoted D. sapinea and other endophytes with a rapid colonisation strategy of N-rich substrates. Asymptomatic trees had a community of endophytes showing a strong negative association with D. sapinea. These antagonistic endophytes were functionally similar to D. sapinea in their response traits to hail, but they were more specialised to proline. The association was conserved across pine species. 5. Our data suggest that after a stress-inducing event, rapid niche occupation is critical for D. sapinea to cause disease. However, competition with other endophytes for key metabolites can supress the pathogen and prevent trees from developing symptoms. 6. Our findings can pave the way to a better understanding of the contribution of latent pathogens on widespread tree mortality events involving abiotic stressors, such as drought, heat or hail.

European ash dieback caused by the alien, invasive ascomycete species Hymenoscyphus fraxineus currently represents, along with its side effects, the greatest threat to common ash (Fraxinus excelsior) trees in Europe. The disease is widely distributed in Germany and present in all regions where common ash is growing. In order to study European ash dieback in Germany and to develop management strategies to conserve common ash as a forest tree species, the concerted, interdisciplinary research project FraxForFuture was initiated. FraxForFuture consist of an association of five sub-networks: FraxConnect, FraxMon, FraxGen, FraxPath, and FraxSilva. In total, 27 individual projects conduct research on the epidemiology of the disease, the pathogen and the preservation of ash, including various control, breeding, and silvicultural strategies. The main goals of the FraxForFuture network and the sub-networks as well as essential information about the network of common research plots are provided.

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