Preparation and antimicrobial activity of O-(benzoyl) chitosan derivatives against some plant pathogens

O-(benzoyl) chitosan derivatives were synthesized and evaluated as antimicrobial agents against some plant pathogens. The chemical structures were characterized by infra-red (IR) and nuclear magnetic resonance (NMR) spectroscopy and the data confirmed that the acylate reaction took place at O-position of chitosan. The antimicrobial activity was investigated against bacteria of Agrobacterium tumefaciens and Erwinia carotovora and fungi of Alternaria alternata, Fusarium oxysporum and Sclerotinia sclerotiorum. Among the derivatives, O-(3,5-dinitrobenzoyl) chitosan was the most active against bacteria of A. tumefaciens and E. carotovora (MIC = 3275 and 3125 mg/L, respectively). However, O-(2-chloro-6-flourobenzoyl) chitosan was the most active in fungal growth inhibition (EC50 = 3040, 1526 and 3301 mg/L for A. alternata, F. oxysporum and S. sclerotiorum, respectively). On the other hand, the derivatives caused significant reduction in spore germination of A. alternata and F. oxysporum with complete inhibition at 1000 mg/L for O-(2-nitrobenzoyl) chitosan and O-(4-chloro-3,5-dinitrobenzoyl) chitosan.   Key words: Antimicrobial activity; O-(benzoyl) chitosan derivatives; degree of substitution; IR and NMR spectroscopy; spore germination.