Large Scale Synthesis of Green Synthesized Zinc Oxide Nanoparticles from Banana Peel Extracts and Their Inhibitory Effects against Colletotrichum sp., Isolate KUFC 021, Causal Agent of Anthracnose on Dendrobium Orchid

Abstract

Fungicides have been extensively used to control fungal diseases that affect several crops including ornamental crops. However, concerns have arisen due to a development of fungicide resistance and increasing incidences of fungicide toxicity effects on nontarget organisms. As zinc oxide nanoparticles (ZnO NPs) have demonstrated effective antimicrobial activity, this study is therefore aimed at synthesizing ZnO NPs from banana peels using a green chemistry method in a large scale and determines their physical properties including their inhibitory effects against a plant pathogen fungus causing anthracnose in orchids, Colletotrichum sp. Results from X-ray diffraction and scanning electron microscope indicated that the synthesized ZnO NPs were obtained without other crystalline impurities, and they were spherical in shape with the average diameter of $256\pm 40\text{nm}$ , respectively. The absorption peak was found to be centered at ~370 nm with the optical band gap value approximately 2.8 eV. Fourier transform infrared spectroscopy analysis confirmed the presence of several functional groups on synthesized ZnO NPs. The total amount of synthesized ZnO NPs was obtained about 170 g for a synthesis reaction. By performing the antifungal activity assay, high doses of green synthesized ZnO NPs significantly inhibited growth of isolated Colletotrichum sp. (KUFC 021) on culture plates. Under greenhouse conditions, high doses of synthesized ZnO NPs also significantly reduced anthracnose symptoms on inoculated orchid leaves with the Colletotrichum sp. (KUFC 021).