Seed Treatment-Based Biocontrol of Tomato Damping off Using Plant Essential Oil and Green Silver Nanoparticles

The fungal pathogen Rhizoctonia solani is a major causal agent of damping-off in tomato plants, leading to severe yield losses worldwide. Conventional fungicides, while effective, raise concerns regarding environmental safety and human health, highlighting the urgent need for sustainable alternatives. In this study, we report for the first time the use of Origanum compactum essential oil to biosynthesize silver nanoparticles and evaluate their antifungal efficacy against Rhizoctonia solani in tomato. This novel approach integrates Moroccan endemic plant resources with nanotechnology for sustainable disease control under both laboratory and greenhouse conditions. The synthesized AgNPs were characterized using UV–Vis spectroscopy, SEM, XRD, and EDX analyses. Tomato seeds were treated with AgNPs and EO and evaluated for germination rate, disease incidence, and seedling growth parameters. Seed germination assays showed that short immersion (2 h) in AgNPs at 50 ppm maintained high germination (92% vs. 85% in control, p < 0.05), whereas prolonged exposure (24 h) completely inhibited germination (0%), confirming dose- and time-dependent phytotoxicity. In vitro assays revealed that AgNPs at 50 ppm inhibited R. solani growth by 93.7%, while EO achieved 62.5% inhibition. Under greenhouse conditions, AgNPs at 50 ppm provided the highest disease suppression (86.5%) and significantly enhanced root/shoot growth and overall seedling vigor. These findings suggest that green-synthesized AgNPs, particularly in combination with EO, represent a promising eco-friendly alternative to conventional fungicides. Further validation under field conditions, along with studies on the molecular mechanisms involved, will be essential to optimize their application in integrated disease management strategies.