Abstract: Some beneficial microorganisms can reduce disease symptoms through activation ofthe induced systemic resistance (ISR). Scarce knowledge is available on the efficacy, persistenceand fitness cost of ISR in non-model systems. Our aim was to characterize the resistance againstPlasmopara viticola activated in grapevine by the biocontrol agent Trichoderma harzianum T39.T39 activated a systemic resistance and reduced downy mildew symptoms at a level comparableto treatments with benzothiadiazole (BTH). However, if only the treated leaves were considered,T39 induced a lower protection level and a shorter persistence of the effect compared to BTH. Inaddition, BTH treatments entailed energy costs, which strongly reduced grapevine growth, butT39 treatments did not affect photosynthesis and plant growth. These results suggest theactivation of different defense pathways in grapevine after BTH and T39 treatment.