Antifungal properties of chitosan-cobalt(II) complex and its potential on the suppression of damping-off in cucumber seedlings

Chitosan-cobalt(II) complex (CTS-Co) was prepared by the complexation of chitosan with cobalt(II) ions. Fourier transform infrared spectra showed that the amine and secondary -OH groups of chitosan were involved in the complexation with Co(II) ions. The resultant CTS-Co exhibited slightly lower thermal stability than chitosan according to the thermogravimetric analysis. Compared with chitosan, CTS-Co possessed much stronger in vitro antifungal activity. The minimum inhibitory concentrations of CTS-Co against three pathogenic fungi were 250-500 mu g/mL, depending on the fungal species. CTS-Co induced the serious leakage of intracellular constituents, which demonstrates that the disturbance on the integrity of the cell membrane is a possible antifungal action of CTS-Co. Furthermore, CTS-Co treatment reduced significantly the disease incidence of damping-off in cucumber seedlings, and the relative control effect reached 72.2-74.3% after 21-day cultivation. Additionally, low molecular weight CTS-Co promoted the growth of cucumber seedlings. Our results suggest that CTS-Co is a possible antifungal agent and has promising potential on the control of pathogenic diseases in crop production. (c) 2016 Curtin University of Technology and John Wiley & Sons, Ltd.