Microbial Allies in the Olive Canopy: Endophyte Composition, Drivers, and their Role in Plant Protection

The olive tree (Olea europaea L.) hosts diverse endophytic microbial communities that contribute to its resilience, productivity, and adaptation to environmental stressors. Since the temperature increases caused by global climate change primarily affects the aerial part of the plant, this review synthesizes current knowledge on the diversity, composition, and ecological drivers of olive phyllosphere endophytes, with a focus on bacterial and fungal communities. We highlight the role of host-related factors-including plant genotype, organ specificity, age, and phenological stage-in shaping microbiota structure across spatial and temporal scales. Genotype consistently emerges as a major determinant of microbial composition, while leaves and twigs harbor distinct yet overlapping communities. Geographic location, environmental variables, and seasonal shifts significantly influence microbial assemblages, with closer sites often supporting more similar communities. We also discuss the impact of agricultural practices and biotic and abiotic stressors on microbiota stability and function. Notably, several cultivable taxa-including Bacillus, Paenibacillus, Pantoea, Aureobasidium, and Penicillium-exhibit antagonistic activity against key olive pathogens, underscoring their potential as biological control agents. We conclude by emphasizing the need for functional studies to elucidate the roles of keystone endophytes and to inform microbiome-based strategies for sustainable olive cultivation.