Efficacy of biosynthesized silver nanoparticles from Larrea tridentata against Clavibacter michiganensis

Green synthesis of silver nanoparticles (AgNPs) from plant extracts is simple, fast and environmentally friendly. In this study, an aqueous extract of fresh leaves from Larrea tridentata was evaluated as a possible source of reducing and stabilizing agents to obtain AgNPs. The synthesized nanoparticles were characterized by X-ray diffraction, revealing the metallic nature of Ag nanoparticles. Transmission electron microscopy (TEM) studies showed spherical nanoparticles with sizes below 28 nm. Furthermore, its bactericidal effect against Clavibacter michiganensis subsp. michiganensis (Cmm) infection in tomato plants was determined. Forty-two days after inoculation with Cmm, the disease incidence in plants with AgNPs did not exceed 20% at 50 mg L-1, and it also reduced disease severity by 36%, which correlates with the inhibition of bacterial growth in the tissue (up to 95%). The physiological analysis also showed the growth-promoting effect of AgNPs in diseased plants, increasing shoot length (22.1%) and root dry weight (25.73%) compared with the pathogenic control. Congruently, AgNPs increased enzyme activity for CAT, APX, POD, and total phenol and flavonoid concentrations in the leaves. Slower symptom development and reduction in bacterial growth in AgNPs-treated plants could be due to this bactericidal activity and the induction of an antioxidative protection system.