Antifungal activity of chitosan-silver nanoparticle composite against Colletotrichum gloeosporioides associated with mango anthracnose

Abstract

Chitosan loaded with various metal ions such as Ag+, Cu2+, Zn2+, Mn2+ and Fe2+ has been reported to exert strong antimicrobial activity. In this study, the silver-nanoparticles (AgNPs) were synthesized at 95°C using chitosan as the reducing agent and stabilizer. The UV-Vis spectrum displayed peak in a range between 415-420 nm, the characteristic surface plasmon resonance band of silver nanoparticles. The size, shape and aggregation properties of the resultant nanoparticles were examined using field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The measurement results indicated that the chitosan-silver nanoparticle (chitosan-AgNP) composite having the mean hydrodynamic diameter range of 495-616 nm were apparently smooth and the silver nanoparticles with the size distribution was from 10 to 15 nm. Chitosan-AgNP composites had a zeta potential of +50.08 mV to +87.75 mV. In vitro conidial germination assay indicated that chitosan-AgNP composite exhibited significantly higher antifungal activity against Colletotrichum gloeosporioides than its components at their respective concentrations. In vivo assay using detached mango fruit cv. Alphonso showed that anthracnose was significantly inhibited by chitosan-AgNP composite. Therefore, this study suggests that postharvest decay in mango can be minimized by chitosan-AgNP composites and its application on a commercial scale needs to be exploited.   Key words: Chitosan, silver nanoparticle, antifungal activity, mango fruits, Colletotrichum gloeosporioides.