Abstract
Bacterial wilt caused by the phytopathogen Ralstonia solanacearum (R. solanacearum) is a devastating plant disease worldwide. The use of bactericides and antibiotics for controlling bacterial wilt has shown low efficiency and posed environmental risks. This study was to phytofabricate silver nanoparticles (AgNPs) mediated by canna lily flower (Canna indica L.), Cosmos flower (Cosmos bipinnata Cav.), and Lantana flower (Lantana camara L.). The biosynthesized AgNPs were confirmed and characterized by UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscopy (SEM). UV-visible spectra showed absorption peak bands at 448, 440, and 428 nm of AgNPs synthesized by C. indica L., C. bipinnata Cav., and L. camara L. flowers, respectively. FTIR spectra confirmed that biofunctional groups of flower extract were involved in the synthesis of AgNPs as capping and stabilizing agents. The spherical AgNPs synthesized by C. indica L., C. bipinnata Cav., and L. camara L. flowers had average diameters of 43.1, 36.1, and 24.5 nm, respectively. The AgNPs (10.0 μg/ml) synthesized by L. camara L. flower had a maximum suppression zone of 18 mm against R. solanacearum strain YY06 compared with AgNPs synthesized by C. indica L. and C. bipinnata Cav. flowers. Bacterial growth, biofilm formation, swimming motility, efflux of nucleic acid, cell death, cell membrane damage, and reactive oxygen species (ROS) generation of R. solanacearum were also negatively affected by AgNPs with high concentration and small size. In summary, the biosynthesized AgNPs can be used as an efficient and environmentally friendly antibacterial agent to reasonably inhibit R. solanacearum.
Highlights
Bacterial wilt caused by the phytopathogen Ralstonia solanacearum is a devastating plant disease worldwide, which can affect more than 200 plant species in over 50 families such as eggplants, tomatoes, olives, groundnuts, potatoes, and bananas (Hayward, 1964; Schell, 2000)
The synthesis of AgNPs through the aqueous flower extracts of C. indica L., C. bipinnata Cav., and L. camara L. was as a result of the reduction of silver ions (Ag+) to Ag0 in AgNO3 (4 mM) solution at the optimum temperature (Figure 1)
The UV-visible spectra of nanoparticles mediated by C. indica L., C. bipinnata Cav., and L. camara L. flowers showed absorption peak bands at 448, 440, and 428 nm, respectively (Supplementary Figure S1)
Summary
Bacterial wilt caused by the phytopathogen Ralstonia solanacearum is a devastating plant disease worldwide, which can affect more than 200 plant species in over 50 families such as eggplants, tomatoes, olives, groundnuts, potatoes, and bananas (Hayward, 1964; Schell, 2000). Compared to biological synthesis of nanoparticle, physiochemical methods have difficulty applying on a large scale owing to the production of high temperature and harmful chemicals (Ahmed et al, 2016) Biological stuff such as plants, bacteria, and fungi were used for green synthesis of AgNPs (Castro-Longoria et al, 2011; Husen and Siddiqi, 2014b), especially plants are more advantageous because of less contamination threat and easy availability. The work of this research was mainly to green synthesize AgNPs mediated by Canna lily flower (C. indica L.), Cosmos flower (C. bipinnata Cav.), and Lantana flower (L. camara L.) and demonstrate the antibacterial activities and mechanisms against the pathogen R. solanacearum of bacterial wilt. To the best of our knowledge, this is the first report to synthesize AgNPs using flower extract of C. indica L. and C. bipinnata Cav
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