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ABSTRACTThis study was aimed at investigating the antimicrobial activity of iron oxide nanoparticles (Fe3O4NPs) and magnesium oxide nanoparticles (MgONPs) against Helminthosporium heveae isolated from diseased rubber leaves. Fe3O4NPs and MgONPs were biologically-synthesized by the reduction of ferric chloride (FeCl3) and magnesium nitrate (Mg[NO3]2) precursor solutions, respectively using neem leaf plant extract. The biologically-synthesized nanoparticles were characterized using Vis-spectrophotometer. H. heveae was isolated from diseased rubber leaves collected from Edo state and the isolate was identified using macroscopy and microscopy. In vitro antimicrobial activities of Fe3O4NPs and MgONPs were investigated using agar well diffusion method. Antifungal activities of different concentrations (25, 50, 75 and 100 %) of Fe3O4NPs or MgONPs were tested against the isolate. FeCl3, or Mg(NO3)2 (precursor solutions), neem leaf plant extract or ketoconazole (antifungal agent) were used as the controls. Zones of inhibition were recorded after 4 days of incubation. The results obtained from the spectrophotometric analysis showed that Fe3O4NPs had absorption peaks at 400 nm and 550 nm wavelengths, while MgONPs had an absorption peak at 400 nm wavelength, indicating nanoparticle synthesis. It was observed from the agar well diffusion experiment that 100 % of Fe3O4NPs produced the highest zone of inhibition with an inhibitory rate of 66 %, while MgONPs did not show any zone of inhibition on the mycelia of H. heveae. Neem plant extract, FeCl3 and Mg(NO3)2 precursor solution also did not inhibit the mycelia growth of H. hevaea. The findings of this research suggest that the biologically-synthesized Fe3O4NPs using neem plant extract possess antifungal property against H. heveae isolated from diseased rubber leaves while MgONPs do not have antifungal property against H. heveae. Further study is required to investigate the possibility of using Fe3O4NPs in managing the disease caused by H. heveae on rubber trees, so as to increase the production of latex, as rubber plant is of great economic importance to a nation’s GDP.
