Unveiling Oak Endophyte Dynamics: Cadophora luteo-olivacea and Trichoderma atroviride from Pathogenicity Tests to Omics Insights

Pedunculate oak (Quercus robur) is a foundation tree species in European forests and reforestation programs, and forest nurseries represent key phytosanitary bottlenecks where asymptomatic planting stock can disseminate cryptic pathogens. Cadophora luteo-olivacea is frequently associated with grapevine trunk diseases and has been recovered from diverse woody hosts, yet its pathogenic potential on oak and its interactions with antagonistic fungi remain unresolved. Here, we combine pathogenicity testing, dual-culture confrontation assays and time-resolved, spatially resolved contact-zone proteomics and metabolomics to connect detection to causality and mechanism in an oak associated Cadophora–Trichoderma system. We fulfill Koch’s postulates for C. luteo-olivacea on Q. robur seedlings and quantify inhibition of Cadophora by a natural isolate of Trichoderma atroviride. Contact-zone proteomics at 4 and 8 days post-contact reveals a staged, interface-localized antagonistic program dominated by fungal cell-wall targeting hydrolases (including chitinases and β-1,3-glucanases), secreted proteases, oxidoreductases, transporters and small secreted proteins, alongside factors consistent with adhesion and self-protection. Together, these complementary assays provide the first experimental evidence that C. luteo-olivacea is pathogenic on Q. robur and delineate mechanistic signatures of T. atroviride mycoparasitism at the interaction front. This framework links nursery-relevant pathogen screening to mechanistic readouts and informs evaluation of biocontrol potential in a foundation forest species.