Original article Antifungal effects of salicylic acid and other benzoic acid derivatives towards Eutypa lata: structure–activity relationship Bénigne-Ernest Amborabé a , Pierrette Fleurat-Lessard a , Jean-François Chollet b , Gabriel Roblin a, * a Laboratoire de physiologie et biochimie végétales, université de Poitiers (CNRS, UMR 6161), station biologique de Beau-Site, 25, faubourg Saint-Cyprien, 86000 Poitiers, France b Laboratoire de synthèse et réactivité des substances naturelles, université de Poitiers (CNRS, UMR), 40, avenue du Recteur-Pineau, 86022 Poitiers, France Received 18 March 2002; accepted 24 June 2002 Abstract 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. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Eutypa lata; Eutypiosis; Phenolics; Salicylic acid; Uptake 1. Introduction In certain plant diseases induced by fungi localized in the woody tissues, curative treatments are difficult to carry out. A strategy may consist in identifying natural molecules with antibiotic properties which can be transported over long distances in the plant towards the fungal target. Considering their known chemical and biological prop- erties, phenolics might fulfill the requirements of such a strategy. Indeed, it has been shown in a wide variety of host/pathogen interactions that phenolic compounds may play a pivotal role in the plant resistance processes. Thus, phenolics such as many benzoic acid derivatives accumulate in plants during the phase of infection [26]. These com- pounds result from the activation of the key enzyme, phenylalanine ammonia lyase, leading from phenylalanine to the formation of various derivatives [15]. Among benzoic acid derivatives, data in the literature show that salicylic acid (SA) may play a central role in plant disease resistance, particularly during systemic acquired resistance (SAR) [32]. Thus, the level of SA increases several fold in tobacco and cucumber after pathogen infection [19,29] and this increase is correlated with SAR [19,21]. Furthermore, transgenic tobacco and Arabidopsis plants that are unable to accumu- late SA due to the expression of the bacterial nahG gene (NahG plants) fail to develop SAR and exhibit increased susceptibility to an infection with virulent and avirulent pathogens [8,13]. The aim of this study was to check the impact of SA on mycelial growth of Eutypa lata (Pers. Fr.)Tul. This fungus is the causal agent of eutypa dieback, a severe disease of the Abbreviations: HEPES, N-[2-hydroxyethyl]piperazine-N'-[2-ethane- sulfonic acid]; MES, 2-[N-morpholino] ethanesulfonic acid; SA, salicylic acid; SAR, systemic acquired resistance * Corresponding author. E-mail address: roblibio@club-internet.fr (G. Roblin). Plant Physiol. Biochem. 40 (2002) 1051–1060 www.elsevier.com/locate/plaphy © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 0 9 8 1 - 9 4 2 8 ( 0 2 ) 0 1 4 7 0 - 5