Antifungal effect of Ag/Cu bimetallic nanoparticles against selected mycotoxin producing fungi on maize

Abstract

Eastern Cape has the highest levels of maize contamination, which is accelerated by poor agricultural practices; therefore monitoring the spread of the contamination is crucial. The aim of this study was to investigate the antifungal effects of Ag/Cu bimetallic nanoparticles (BMNPs) against the selected mycotoxin causing fungi in maize. Stored maize samples with visible contamination were collected from Centane region in the Eastern Cape. Pathogens were isolated and their molecular identification was done using the Polymerase chain reaction (PCR). Fusarium verticillioides (F. verticillioides), Fusarium oxysporum (F. oxysporum) and Aspergillus flavus (A. flavus) were obtained. The nanoparticles were synthesized using chemical reduction method and characterized using ultra-violet visible spectroscopy (UV-Vis) and transmission electron microscopy (TEM) prior evaluation. The antifungal activity of Ag/Cu bimetallic nanoparticles against F. verticillioides, F. oxysporum and A. flavus was investigated through an agar diffusion and spiral gradient methods. Data collected was analysed statistically using Analysis of Variance (ANOVA) on GenStat 20th edition. The mycelial growth was observed after 7 days and the investigations from this study resulted into nanoparticles (NPs) of an average size of 26, 10, ~5 and 6 nm for Ag, Cu, Ag/Cu and Cu/Ag, respectively. The antifungal activity of Ag NPs was found to be slightly stronger than that of the both controls (AgNO3 and Cu(OA)2) against F. verticilliodes. Moreover, BMNPs showed improved percentage inhibition (61.0 %) against A. flavus as compared to their counterparts’ monometallic NPs (42.0 % and 36.0 %). Cu/Ag BMNPs revealed to have almost equal efficacy in comparison with Ag/Cu BMNPs regardless of their size. The minimum inhibitory concentration of Cu NPs against F. oxysporum was observed to be 17.61 μg/mL, while that of Cu/Ag BMNPs was observed to be 12.89 μg/mL. The percentage difference between treatments was also evaluated in order to determine the strength of the NPs to each other. This study demonstrated that NPs exhibited reasonable antifungal activity against the tested crop fungal pathogens. Therefore, they may benefit the agricultural sector for the management of fungal pathogens, particularly those which are associated with post-harvest storage.