Application of Nanostructured Semiconductor Oxides TiO2-Based as Additives in the Germination Process of Alfalfa

Nanotechnology has emerged as a promising approach to enhance agricultural productivity; in this context, the effects of nanoparticles (NPs) on plants depend strongly on their size, composition, and concentration. We evaluated the influence of titanium dioxide (TiO2) and silver-doped titanium dioxide (Ag-TiO2) nanoparticles on seed germination, early growth, metabolite production, and antioxidant responses in alfalfa (Medicago sativa L.). Nanoparticles were synthetized via sol–gel; titanium isopropoxide was used as precursor and isopropanol as organic solvent, silver nitrate was used as dopant. Seeds were treated with nanoparticle suspensions at 0, 1, 5, 10, and 15 ppm. Morphological parameters (germination rate, radicle length, fresh weight, leaf morphology, and chlorophyll index), total phenols, flavonoids, and antioxidant capacity (DPPH and ABTS assays) were evaluated. Results showed a concentration-dependent response in morphological characteristics. TiO2 promoted radicle elongation at 10 ppm (16%) and increased chlorophyll index along all concentrations (from 7% to 17%) but inhibited leaf growth at both 1 and 15 ppm (from 49% to 59%). In contrast, Ag-TiO2 enhanced germination percentage by up to 95% and phenolic accumulation at 5 and 15 ppm (p < 0.05), although leaf length was consistently reduced across all concentrations (from 11% to 17%). Flavonoid levels increased by up to 116% at concentration of 15 ppm (p < 0.05). Antioxidant activity exhibited a contrasting pattern: TiO2 reduced radical scavenging capacity when applied at 10 and 15 ppm, against the control group, from 48.62% to 17.72% and 13.96%, respectively, while Ag-TiO2 maintained the antioxidant capacity when applied at 1 ppm. These findings suggest that nanoparticles in fact influence the germination process and have a noticeable effect on the morphological characteristics of alfalfa’ sprouts.