In vitro assessment of N-(benzyl)chitosan derivatives against some plant pathogenic bacteria and fungi

Plant pathogenic bacteria and fungi negatively affect a large number of important fruit and vegetables during the growing season and throughout postharvest storage. Therefore, the current study focuses on the preparation of N-(benzyl)chitosan derivatives as antimicrobial agents to control these microorganisms. Chitosan was reacted with a set of aromatic aldehydes by reductive amination involving formation of the corresponding imines, followed by reduction with sodium borohydride to produce the N-(benzyl)chitosan derivatives. The end products were analyzed using 1H NMR spectroscopy and the degrees of substitution ranged from 0.12 to 0.29. The antibacterial activity was evaluated in vitro against the crown gall disease Agrobacterium tumefaciens (Family: Rhizobiaceae; Class: Alpha Proteobacteria) and the soft mold disease Erwinia carotovora (Family: Enterobacteriaceae; Class: Gamma Proteobacteria) by the nutrient agar dilution method. A higher activity of chitosan and its derivatives was obtained with N-(o-ethylbenzyl)chitosan with a MIC of 500 mg/L against E. carotovora, while N-(o,p-diethoxybenzyl)chitosan was the most active one against A. tumefaciens with a MIC of 1050 mg/L. In addition, the in vitro antifungal assessment against root rot disease Fusarium oxysporum (Family: Tuberculariaceae; Class: Deuteromycetes) and the leaf spots and blights disease Pythium debaryanum (Family: Pythiaceae; Class: Oomycetes) was tested by a mycelial radial growth technique. The data showed that N-(o,p-diethoxybenzyl)chitosan was the most active one with an EC50 of 400 and 468 mg/L for F. oxysporum and P. debaryanum, respectively. In addition, chitosan derivatives had a detrimental effect on spore germination for F. oxysporum. Most of these derivatives exhibited high inhibition percentage (>90%) of spore germination at 1000 mg/L.