Anti-phytopathogenic fungal activity of benzoic acid and cinnamic acid derivatives

Abstract

Screening of antifungal activity of forty benzoic acid derivatives and related compound and fifty cinnamic acid derivatives were evaluated on four phytopathogenic fungi; Alternaria porri, Fusarium oxysporum, Pestalotiopsis sp. and Phytophthora parasitica, in order to define a possible structure-activity relationship. The addition of a supplementary hydroxyl group in various positions on the benzene ring of benzoic acid suppressed the antifungal activity on all tested fungi. On the contrary, the addition of a chlorine in the 2 or 3 position and conversion of carboxylic acid function group to an aldehyde increased the mycelial growth inhibition. Further evaluation of antifungal activity of cinnamaldehyde found that it completely suppressed A. porri, F. oxysporum and P. parasitica at 2.5 mM and nearly completely suppressed Pestalotiopsis sp. Methyl. ethyl, propyl, butyl, hexyl, octyl and dodecyl 4-hydroxybenzoates were tested against A. porri, Pestalotiopsis sp. and P. parasitica, in order to investigate the structure-activity relationship on the length of alkyl chain. The results showed that butyl 4-hydroxybenzoate showed generally good activity against all tested fungi. Further evaluation of antifungal activity, phytotoxicity and stability of 2,6-dichlorocinnamic acid were determined. It was found that compared to the conventional chemical fungicide captan and iprodione, 2,6-dichlorocinnamic acid is much more efficient and therefore can be an antifungal agent, particularly to control Pestalotiopsis sp. and P. parasitica.