In a previous study, we isolated and characterized the Thctf1 transcription factor of Trichoderma harzianum, which showed a significant role in the production of secondary metabolites derived from 6-pentyl-2H-pyran-2-one (6PP) and in the antifungal activity of the fungus.In this work, we have studied the effect of this gene in the interaction of T.harzianum with tomato plants as 6PP-derived compounds have been related with the plant growth.With this aim, we treated tomato plants with spores of T.harzianum wild type or disruptants lacking of the functional Thctf1 gene, and we evaluated the development and the defense responses of the plants.