Antifungal effects of salicylic acid and other benzoic acid derivatives towards Eutypa lata: structure–activity relationship

Salicylic acid (SA) inhibited mycelial growth of Eutypa lata (Pers. Fr.)Tul. in a solid as well as in a liquid culture medium, in a concentration-dependent manner, the threshold value being 0.1 mM. In conditions mimicking the plant environment (in particular, a pH near the apoplastic value, i.e. 5.5), 1 mM SA showed only fungistatic properties. However, modifications were observed in the structural organization of the mycelium at various levels (wall, mitochondria, vacuole and nucleus). A fungicidal effect was obtained at 2 mM or higher concentrations and following this treatment, fungal filaments appeared empty. Antifungal efficiency of the molecule was increased when the experimental pH was brought to more acidic values (pH 4). This observation was correlated with the increased capacity of compound uptake by the fungus. The in vitro antifungal effects of 57 benzoic acid derivatives were investigated on E. lata, in order to define a possible structure–activity relationship. A strategy leading to the synthesis of particular benzoic conjugates and integrating the data obtained here is proposed to treat in planta against E. lata, the causal agent of eutypa dieback, a severe disease of the grapevine and other woody plants resulting from an infection in the xylem of the host plant.