P-121 - Identification of biocontrol yeasts that inhibit Pseudomonas syringae infection through inducing systemic acquired resistance

Biocontrol microorganisms play an important role in sustainable agriculture by offering an environmentally friendly alternative to chemical pesticides. Their ability to enhance plant health and resilience relies on mechanisms such as competition, antagonism, and the induction of plant defense pathways, including Systemic Acquired Resistance (SAR). This study aims to provide new insights into the exploitation of epiphytic yeasts for the control of plant diseases through the induction of SAR. Different strains of epiphytic yeasts were evaluated in vitro for their capacity to induce defense responses in an Arabidopsis thaliana transgenic reporter line expressing the PR1–β-glucuronidase (GUS) promoter fusion. Seedlings at the rosette stage were inoculated with a yeast strain two days prior to GUS staining, and the resulting blue coloration intensity was quantified using ImageJ. The GUS-induced phenotypes were then validated by RT-qPCR measurement of PR2 expression. Finally, the effects of selected yeasts were evaluated in vitro on wild-type Arabidopsis plants (Col-1) for their antibacterial activity against Pseudomonas syringae pv. tomato DC3000 (Pst). Yeast suspensions were sprayed onto plants at the rosette stage, two days before inoculation with a Pst suspension. Disease symptoms and the Pst population were evaluated. Our results indicate that the tested epiphytic yeast strains can stimulate plant defense mechanisms and confer partial resistance against bacterial pathogens.