Acrylpimaric acid-modified chitosan derivatives as potential antifungal agents against Valsa Mali

In order to the antifungal activity of chitosan (CS) and to obtain a better natural bio-antimicrobial agent, CS was modified with acrylpimaric acid (APA). The grafting sites of APA on CS were controlled by adjusting the reaction time and the ratio of reactants to obtain APA grafted with CS C₂-NH₂ (NCSAA) and C₆-OH (CSAA). Intermediates to protect C₂-NH₂ (PMCSAA) and final sample derivatives (PCSAA) were prepared using phthalic anhydride. The structural and crystal variations of the four derivatives were analyzed and determined by FTIR, ¹H NMR and XRD. The in vitro antifungal activities of the four modified samples against V. mali, C. lunata, A. solani, F. oxysporum f. sp. niveum, and F. graminearum were evaluated by the mycelial growth rate method, and PCSAA was screened for optimal inhibitory effect on V. mali with an EC₅₀ = 38.66 μg/mL. The SEM and TEM showed that these derivatives cause the loss of mycelial contents by disrupting the ultrastructure of the mycelium, destroying the internal structure of the mycelium, and preventing the cells from carrying out their normal life activities. In vivo experiments showed better curative effect (79.09 % ± 2.00) and protective effect (80.93 % ± 0.03) of PCSAA at 200 μg/mL.