A Complex Interaction System for Understanding the Ability of Trichoderma to Trigger Defenses in Tomato Plants Challenged by Phytophthora nicotianae

In this study, the early activation of plant-defense-related genes during a three-way plant–antagonist–pathogen interaction in a tomato–Trichoderma–Phytophthora nicotianae model system was evaluated. Thirty-day-old tomato seedlings were treated at the root systems with a suspension of germinated conidia of two selected strains of T. asperellum and T. atroviride and then inoculated with zoospores of P. nicotianae. The defense mechanisms activated by tomato plants upon the simultaneous colonization of the root systems by Trichoderma spp. and P. nicotianae were evaluated 72 h post-inoculation by analyzing the transcriptomic profiles of genes involved in the pathways of salicylic acid (i.e., pathogenesis-related proteins—PR1b1 andPR-P2-encoding genes), jasmonic acid (i.e., lipoxygenases enzymes—TomLoxC- and TomLoxA-encoding genes), and the tomato plant defensin protein (i.e., SlyDF2-encoding gene). The results showed that PR1b1 was more strongly up-regulated in the three-way system including T. asperellum, while the gene PR-P2 was up-regulated in the system including T. atroviride. TomLoxA was significantly up-regulated only in the three-way system including T. asperellum, while TomLoxC was significantly up-regulated in neither of the analyzed three-way systems. Finally, the gene SlyDF2 was significantly up-regulated in tomato seedlings in both three-way systems