Green synthesis of Callicarpa tomentosa routed zinc oxide nanoparticles and their bactericidal action against diverse phytopathogens

In recent years, the synthesis of zinc oxide nanoparticles (ZnO NPs) using plants is gaining momentum owing to their antibacterial potency. In this study, we investigated the biogenic synthesis of ZnO NPs using leaf extract of the medicinal plant Callicarpa tomentosa . The synthesized ZnO NPs were evaluated for their antimicrobial efficacy against Xanthomonas oryzae , Pseudomonas syringae , Xanthomonas campestris , and Ralstonia solanacearum . The ZnO NPs were characterized by UV–vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electron microscopy, energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The nanoparticles displayed a promising antimicrobial activity and significant inhibition zone (37.2 mm) when tested against Ralstonia solanacearum at 100 µg/mL. The minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) of ZnO NPs were detected at 250 and 125 µg/mL, respectively. Fluorescence microscopy–based determination of the antibacterial activity was used to study the morphological changes caused in the test bacteria. The ZnO NPs exhibited anti-biofilm activity that was evident in the inhibition of biofilm formation by R. solanacearum . Tomato seedlings treated with ZnO NPs at 100 μg/mL and challenged with pathogen showed 38% disease incidence and 57% protection against wilt disease as compared to the untreated pathogen-inoculated tomato seedlings (95%). Increase in plant growth parameters such as plant height, shoot length, root length, stem growth, fresh weight, and dry weight was seen in seedlings treated with ZnO NPs. Overall, these results suggest that the ZnO NPs synthesized from C. tomentosa leaf extract exhibit remarkable antibacterial properties against the broad spectrum of phytopathogenic bacteria. Thus, the eco-friendly synthesized ZnO NPs can be used as a potential candidate in agriculture for the effective management of plant diseases and particularly bacterial wilt disease in diverse crop plants. Graphical abstract