Hybridization of Chitosan and Biosynthesized Silver Nanoparticles to Enhance Antimicrobial Activity against Phytopathogens in Tomato (Solanum lycopersicum)

Chitosan-hybridized biogenic silver nanoparticles (Ch@BSNP) were synthesized with the extracellular metabolites of Trichoderma viride. Chitosan hybridization- and T. viride-derived compounds associated with the particles were confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM)-energy dispersive X-ray analysis (EDX), and gas chromatography–mass spectrometry (GC–MS) analysis. The particles had a ζ-potential 19.2 mV and a hydrodynamic size of 97.74 nm with a polydispersity index (PDI) of 0.198. TEM analysis revealed particles of spherical shape and actual size range between 30 and 35 nm. The antimicrobial activity of these particles was compared to chitosan alone and nonhybridized particles against three bacterial phytopathogens, viz, Pseudomonas syringae, Erwinia chrysanthemi, and Xanthomonas campestris. The zone size was 50.0, 29.75, and 34.00 mm with Ch@BSNP, respectively, while the corresponding values for BSNP were 29.75, 23.5, and 18.00 mm. In a liquid culture assay, exposure to Ch@BSNP significantly decreased the size of bacterial cells from 3905.00 to 2711.00 nm for P. syringae, from 3484.00 to 3386.00 nm for E. chrysanthemi, and from 7823.33 to 5956.33 nm for X. campestris. Similar increased activity of Ch@BSNP was also observed against four fungal plant pathogens, viz, Sclerotium rolfsii, Rhizoctonia solani, Alternaria alternata, and Alternaria brassicicola. The Ch@BSNP also demonstrated lower toxicity on noncancerous human cell lines than antimicrobial efficacy. In a greenhouse study, Ch@BSNP reduced the leaf spot disease incidence in tomato by up to 60% and also enhanced several physical and physiological attributes, viz, root and shoot lengths, fresh and dry weights, and chlorophyll and carotenoid contents compared to the diseased plant. These observed beneficial effects and overall biocompatibility of Ch@BSNP suggest that this material may be a safe and effective antimicrobial bioagent for sustainable nano-enabled agriculture.