Molecular characterization of induced resistance in grapevine: relevance of plant genotype and exposure to abiotic stresses

Enhancement of plant resistance is a promising alternative to chemical fungicides for controlling crop diseases, but its efficacy is affected by several factors. In order to further optimize the use of resistance inducers against downy mildew of grapevine, we characterized the molecular mechanisms activated by the beneficial microorganisms Trichoderma harzianum T39 (T39). T39 treatment directly activated the complex microbial recognition machinery and improved the phosphorylation of proteins of the signal transduction cascade. Transcriptomic and proteomic analyses revealed that T39-induced resistance partially inhibited disease-related processes and specifically activated defence responses after pathogen inoculation. However, the efficacy of T39-induced resistance was significantly affected by abiotic stresses and grapevine genotype. Combined heat and drought stresses reduced the efficacy of T39 and attenuated the modulation of defence-related genes. Moreover, expression analysis of biomarkers of T39-induced resistance highlighted complex differences among grapevine cultivars. These results demonstrated that abiotic stresses and cultivar responsiveness should be carefully considered to maximize the effect of resistance inducers.