Green synthesis of Cu₂O nanoparticles: characterization and application to control tobacco mosaic virus infection

Significant opportunities exist for the innovative development and use of NPs for plant protection. Here we report the green synthesis of cuprous oxide (Cu₂O)-NPs using menteng fruit (Baccaurea racemosa) extracts. We determined the best application time and concentration to control tobacco mosaic virus (TMV) in Chenopodium amaranticolor and tested the efficacy of the NPs on chili peppers either before or after inoculation with TMV. On the basis of transmission electron microscopy, X-ray diffraction, and UV–visible spectral data, the Cu₂O-NPs are spherical particles with an average diameter of 5.1 nm, have a well-crystallized structure with a crystallite size of 4.3 nm, and a specific absorption at 400–500 nm, respectively. Based on Fourier-transform infrared spectra, B. racemosa fruit extracts acted as reducing and capping agents for biosynthesizing Cu₂O-NPs. Bioassays on indicator plants indicated that Cu₂O-NPs were most effective against TMV when sprayed at 80–100 ppm on plants after infection. Applying Cu₂O-NPs on chili pepper did not increase peroxidase activity compared to the untreated control. Among the concentrations tested on chili pepper, 100 ppm was the best; disease severity and TMV titer were significantly lower compared to the untreated control. Applying Cu₂O-NPs caused fracture and aggregation of the viral particles, indicating their antiviral potential. The Cu₂O-NPs also stimulated growth of the chili pepper plants, indicating their potential as plant growth promotors.