Abstract: Biochar is the solid product of biomass pyrolysis. Recently, biochar has been found to induce systemic resistance to foliar pathogens of tomato, sweet pepper and strawberry. In this study, we investigated the induced resistance pathway that is mediated by biochar in the tomato – Botrytis cinerea pathosystem. Greenhouse waste biochar that was produced at 350 and 450°C (GHW-350, GHW-450) and included in the potting mix at a rate of 1 or 3% (w/w) induced resistance to B. cinerea in tomato. Despite the fact that different biochars were used and the fact that the effects of particular biochar varied in a cultivar-dependent manner, disease severity was significantly reduced in all of the tested tomato cultivars. The addition of GHW-450 to the potting mix induced resistance to B. cinerea in an ethylene-insensitive mutant, Never ripe, and in a transgenic tomato line that cannot accumulate salicylic acid (NahG), but not in a jasmonic acid-deficient mutant, def1. The addition of biochar to the potting mix induced the expression of PI2, TomLoxA, TomLoxC, TomLoxD, Pti4, Pti5, GluB, CHI9, SAMT, ACO1, and PR1a at least in one of the genotypes. Similarly, following B. cinerea infection, the transcription levels of the rest the genes mentioned, except for TomLoxA and TomLoxC, increased. However, in the case of the def1 mutant, the presence of biochar in the potting mix hardly affected the expression of these genes. In conclusion, the results of our quantitative disease assay and the observed induction of gene expression strongly suggest that the jasmonic acid-signaling pathway plays an important role in the biochar-mediated resistance to B. cinerea observed in tomato.