Abstract: Plasmopara viticola, the causal agent of downy mildew, is one of the most damagingdiseases of grapevine (Vitis vitifera) worldwide. In grapevine, Trichoderma harzianum T39activates a plant-mediated systemic resistance and significantly reduces downy mildewsymptoms. Preliminary results suggest an implication of T39 biological status (i.e. grownconditions and ages of conidia) in the biocontrol efficacy. To further understand the mechanismsof T39-induced resistance, we aimed to characterize the fungal features for an efficient selfprotectionactivation in grapevine. By the parallel characterization of fungal and plant genes, theimpact and properties of the resistance inducer will be determined. This study will help tounderstand the role of physiological factors in the efficacy of biocontrol agents, in order tomaximize their effect especially during changes of abiotic conditions.