Oxidized of chitosan with different molecular weights for potential antifungal and plant growth regulator applications.

The application of Chitosan (CS) in drug delivery systems, plant growth promotion, antibacterial potentiality and plant defense is significantly limited by its inability to dissolve in neutral solutions. In this work, CS with different molecular weights (Mw) has been oxidized, yielding five kinds of oxidized chitosan (OCS 1-5) with solubilities in neutral solutions. The results obtained from Fourier Transform Infrared Spectroscopy clearly showed the successful oxidation of the hydroxyl group to form aldehyde and carboxyl groups. And the CS derivatives showed the wrinkled and lamellar structures on the surface of OCS. The results of antifungal activity against Fusarium graminearum showed that the OCS dissolved in 2 % (V/V) acetic acid exhibited better performance of almost complete inhibition of mycelial growth compared with CS at the concentration of 500 µg/mL. Among the five OCS, OCS-4 exhibited the best antifungal effect and had the lowest EC50 value of 581.68 µg/mL in samples. OCS-4 displayed superior promoting effect on seed germination with a germination potential of 62.2 % at a concentration of 3 g/L and a germination rate of 74.5 %. Additionally, the other four OCS also showed excellent antifungal activity with dose-dependent manners. These results indicated that the OCS had excellent antifungal potential in agricultural production.

Evaluation of sulfonated oxidized chitosan antifungal activity against Fusarium graminearum.

Chitosan biomaterials are widely used in the biological area because of their broad-spectrum antibacterial activity. However, chitosan cannot be dissolved in a neutral solution, limiting its application in various fields seriously. In this study, water-soluble sulfonated oxidized chitosan (SOCS) with antifungal activity were prepared by oxidization and sulfonation. Its structure was clearly confirmed by spectroscopy data (FTIR, 1H NMR, 13C NMR) and elemental analysis. SEM images of OCS and SOCS revealed that there was a little curly and an irregular sheet-like morphologies on them which was attributed to the oxidation and sulfonation on CS. Moreover, the FTIR and NMR indicated that -OH on the CS was oxidized into -COOH on the OCS and -SO3H groups on the SOCS. The EDS results of OCS and SOCS confirmed the presence of the oxygen element in OCS and the S element in SOCS. All studies confirmed the OCS and SOCS were synthesized successfully. Furthermore, the inhibitory activity of SOCS biocomposites against plant pathogenic fungi, (Fusarium graminearum), was investigated. The results showed that the SOCS have significant inhibitory effects on the mycelial growth of F. graminearum. The EC50 value of SOCS against F. graminearum is 79.46 µg/mL. The research results presented above indicated that SOCS can be used as a candidate material for the control of plant pathogenic fungi, and can broaden the application of chitosan materials in plant protection and sustainable agriculture.Research highlightsSOCS showed better solubility in deionized water.The antifungal effect of SOCS dissolved in acetic acid was higher than that of CS dissolved in acetic acid.SOCS dissolved in water can cause an inhibitory effect on F. graminearum at lower concentrations.