Forests cover over 40 % of the EU’s land area, composing a massive, multifunctional green infrastructure with significant economic, social and environmental importance for European citizens. Forest diseases are an increasing threat to forest ecosystems, causing a huge economic and environmental impact on forests worldwide. Invasive alien pathogens and emerging infectious diseases are an unprecedented threat to the capacity of European forests to supply the growing bioeconomy with renewable biomass, carbon sequestration, and other essential ecosystem benefits. One of the most serious concerns in European forests and nurseries is the upsurge of damages caused by invasive, fungal-like, oomycetes Phytophthora species. To strengthen the biosecurity against these pathogens, new, science-based, and socially acceptable forest protection solutions need to be developed. The MSCA-IF RESISTREE project has targeted central knowledge gaps related to a crucial phase of a biological invasion, the establishment phase. Specifically, it has delivered information about the host phenotypic traits and associated mycobiome that can suppress the establishment of Phytophthora species in European forests. We have tested the following hypotheses (1) Endophyte assemblages differ between healthy and Phytophthora-infected trees; (2) Certain endophytic fungi (individual species or groups) limit the growth of Phytophthora-species through different mechanisms; (3) Lesion formation in beech tissues depends on the quality or quantity of endophytic infections in the tissue, and (4) Phytophthora root infection influences the growth and morphology of seedlings before visible symptoms appear.
