Matricaria chamomilla flower extract was used as a biocompatible material for synthesis of zinc oxide nanoparticles (ZnONPs). The synthesized NPs were evaluated for their antibacterial potential in vitro and in vivo against the Gram-negative bacterium Ralstonia solanacearum, which causes devastating bacterial wilt disease in tomato and other crops. Synthesized ZnONPs were further analyzed by UV-visible spectroscopy, Fourier transform infrared spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopy. The synthesized polydisperse ZnONPs were found to be in the size range of 8.9 to 32.6 nm, and at 18.0 µg ml-1 exhibited maximum in vitro growth inhibition of the pathogen R. solanacearum. Scanning electron microscopy analysis of affected bacterial cells showed morphological deformation such as disruption of the cell membrane and wall, and the leakage of cell contents. Results of in vivo studies also showed that application of ZnONPs to the artificially inoculated tomato plants with the pathogen R. solanacearum significantly enhanced the plant growth by reducing bacterial soil population and disease severity as compared with the untreated control. Biosynthesized ZnONPs could be an effective approach to control the bacterium R. solanacearum.
Keywords: biocontrol; nanotechnology; plant pathogen; soil treatment.