Antibacterial Efficacy of Green Synthesized Silver Nanoparticles Using Salvia nubicola Extract against Ralstonia solanacearum, the Causal Agent of Vascular Wilt of Tomato

Ralstoniasolanacearum is a phytopathogen causing bacterial wilt diseases of tomato and affectingits productivity, which leads to prominent economic losses annually.As an alternative to conventional pesticides, green synthesized nanoparticlesare believed to possess strong antibacterial activities besides beingcheap and ecofriendly. Here, we present the synthesis of silver nanoparticles(Sn-AgNPs) from medicinally important aqueous plant extracts of Salvia nubicola. Characterization of biologicallysynthesized nanoparticles was performed through UV-vis spectrophotometry,Fourier transform infrared spectroscopy (FTIR), energy-dispersiveX-ray spectroscopy, X-ray diffraction, scanning electron microscopy,transmission electron microscopy (TEM), and thermogravimetric analysis.The antibacterial activity of the biosynthesized silver nanoparticleswas tested against the phytopathogen R. solanacearum through in vitro experiments. Preliminary phytochemical analysisof the plant extracts revealed the presence of substantial amountsof flavonoids (57.08 mg GAE/g), phenolics (42.30 mg GAE/g), tannins,and terpenoids. The HPLC phenolic profile indicated the presence of25 possible bioactive compounds. Results regardinggreen synthesized silver nanoparticles revealed the conformation ofdifferent functional groups through FTIR analysis, which could beresponsible for the bioreduction and capping of Ag ions into silverNPs. TEM results revealed the spherical, crystalline shape of nanoparticleswith the size in the range of 23-63 nm, which validates SEMresults. Different concentrations of Sn-AgNPs (T1 (500 & mu;g/mL)to T7 (78.1 & mu;g/mL)) with a combination of plant extracts (PE-Sn-AgNPs)and plant extracts alone exhibited an efficient inhibition of R. solanacearum. These findings could be used asan effective alternative preparation against the bacterial wilt oftomato.