A plant-based biocontrol product confers protection against Phytophthora infestans and triggers tomato defense responses

Phytophthora infestans , causal agent of late blight, is mainly controlled with fungicides, whose use is increasingly restricted in Europe, motivating the adoption of sustainable alternatives. Among these, plant-based biocontrol products, particularly those with elicitor and/or priming effects, offer promising perspectives. This study evaluated the protective action of a biocontrol formulated product (FV), derived from plant extracts, against tomato late blight. Greenhouse and growth chamber experiments were conducted to evaluate FV’s preventive efficacy and to distinguish its direct effect from its indirect effect. FV provided protection against late blight as early as 2 hpt (hours post-treatment) and up to 8 dpt (days post-treatment). However, FV did not protect newly formed leaves at 8 dpt. FV application induced tomato defense responses at all time points, with a peak at 6 hpt, notably activating PR2 , PR5 , POX , and ACCO genes expressions. No priming effect on defense gene expression was observed following pathogen inoculation at 2 days post-inoculation (dpi). Additionally, FV’s efficacy was reduced by washing leaf surface, suggesting the contact-dependent action mode. Overall, the results indicate that the product’s efficacy is mainly attributable to a direct effect, accompanied by the activation of tomato defense responses prior inoculation, but without evidence of systemic activity. Moreover, FV-induced protection can be compromised by wash-off of treated leaves and seems to not extend to leaves that are still developing. Although the results are promising, further research is required to clarify the mode of action of this biocontrol product and to assess the potential contribution of induced tomato defense responses to its overall efficacy. • Plant-based biocontrol product effectively controls tomato late blight in planta • Biocontrol product reduced necrotic zones and sporulation of Phytophthora infestans • Biocontrol product protects tomato from 2 h to 8 days after treatment • Transcriptomics showed biocontrol product induced tomato defenses post treatment • Biocontrol product efficacy involves direct and indirect effects on late blight