Exserohilum rostratum-Mediated Synthesis of Silver Nanoparticles: A Case Study on Their Bioherbicidal Activity Against Leptochloa chinensis (L.) Nees

The interdisciplinary progress in nanotechnology has yielded environmentally friendly and cost-effective strategies to enhance bioherbicidal efficacy. This study presents the biosynthesis of silver nanoparticles (M-AgNPs) using the fungus Exserohilum rostratum, specifically targeting the Leptochloa chinensis weed in paddy fields. The M-AgNPs were characterized with an aqueous solution size of 107.9 nm and a zeta potential of −24.0 ± 0.20 mV, and their properties were analyzed by UV-Vis spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The application of M-AgNP suspension at different concentrations of 70 µg∙mL−1, 80 µg∙mL−1, and 100 µg∙mL−1 to L. chinensis at the 3–4 leaf stage resulted in significant herbicidal effects. These nanoparticles induced oxidative stress and significantly reduced the activities of peroxidase, catalase, and superoxide dismutase in the weed seedlings. Meanwhile, M-AgNP treatments significantly increased the activity of cell wall-degrading enzymes, including polygalacturonase and cellulase, in L. chinensis leaves and caused organelle damage in plant leaf cells. Safety assessments showed no significant impact on rice growth after treatment with M-AgNP3 (100 µg∙mL−1) suspension. Our results suggest that M-AgNPs represent a sustainable and eco-friendly approach to weed control that is compatible with rice cultivation, thus supporting the adoption of green agricultural practices.