In nanotechnology, fungal mediated green synthesis of silver nanoparticles (AgNPs) has tremendous application in the development of antimicrobial systems but the mechanism behind the synthesis is yet to be understood. This study aims to synthesize the silver nanoparticles via a green chemistry route using mycellial aqueous extract of agriculturally beneficial fungi Trichoderma harzianum. Two different concentrations (1 mM and 2.5 Mm) of aqueous silver salt (AgNO3) were used and mixed as 1:1 ratio with aqueous extract of T. harzianum at room temperature and the pH of the reaction mixture was monitored until it stabilized. Formation of AgNPs was confirmed by using UV-Vis spectroscopic analysis. For further insight, AgNPs were characterized by using HR-TEM and XRD, which clearly showed appearance of crystalline, monodispersed round-shaped particles of 3-20 nm in size. The synthesised NPs were subjected to antimicrobial assay against gram +ve and gram –ve bacteria using the disk diffusion method. The focused species was Clavibactermichiganensis subsp michiganensis, which is the causitive pathogen of Tomato canker disease and we hypothesised that the synthesised AgNPs might be useful to control this pathogen. Appreciable antibiotic activity was monitored even at a low concentration of 1mM level, while the zone of inhibition was positively increased at 2.5 mM. Our results clearly indicate that the present process is an excellent candidate for industrial scale production of AgNPs, and has the potential to control the bacterial pathogen cmm.

This study investigated the effect of biogenic AgNPs on seed germination and seedling growth of Solanum lycopersicum. Treatment with silver nanoparticles (AgNPs) showed a significantly high germination rate and seedling growth compared to untreated seeds. Furthermore, its bactericidal effect against bacterial pathogen Clavibacter michiganensis subsp. michiganensis (cmm) infection in Solanum lycopersicum was also determined. Bacterial canker of tomato (BCT) caused by cmm results in reduced plant growth and production leading to considerable economic losses. Herein, fungal extracts of T. harzianum and A. fumigatus were used separately as a reducing agent to synthesize AgNPs of varying concentrations (0.088 mg/L, 0.176 mg/L, and 0.44 mg/L). Results suggested that the biosynthesized AgNPs not only worked as bactericide but also completely inhibited the incidence of cmm infection even at the lowest concentration of 0.088 mg/L under greenhouse conditions. Plants treated with AgNPs showed significantly enhanced growth parameters including plant height (cm), tomato yield/plant (g), fresh biomass (g), number of shoots/plant, root weight (g), and dry biomass (g). So, in order to reduce the toxic effects of chemical-based bactericides, biobased AgNPs are recommended, not only to control but also to prevent the bacterial infection in agriculture.

Bacterial canker of tomato caused by the bacterial pathogen Clavibacter michiganensis subsp. michiganensis (Cmm) is a major limiting factor for tomato production worldwide. Currently there exists no resistant variety of tomato to bacterial canker; only cultural and chemical controls are available. This study synthesized AgNPs (silver nanoparticles) via a green chemistry route and investigated their bactericidal potential against bacterial canker of tomato (BCT). AgNPs were prepared using mycellial aqueous extract of agriculturally beneficial fungi Pythium oligandrum. The formation of AgNPs was confirmed by using UV–Vis spectroscopy for the absorbance pattern while their morphology was investigated by the transmission electron microscopy (TEM). The X-ray diffraction profile for the biogenic AgNPs confirmed a crystalline structure with an average particle size of 12 nm. AgNPs treated seeds showed a normal germination rate with normal seedling growth. An in-vitro study found that the prepared AgNPs caused the maximum inhibition of the bacterial pathogen. In the greenhouse the introduction of AgNPs significantly prevents and inhibits the bacterial pathogen Cmm on tomato plants. These results suggest that this process is a strong candidate for industrial scale production of AgNPs. These particles act as an inhibitor and broad spectrum antibacterial agent against cmm, and hence offer a new and eco-friendly alternative in BCT control.