Green nanoparticles of Ag, SiO2, and CeO2: strategy for controlling the PVY and ToBRFV coinfection in bell pepper

Bell pepper (Capsicum annuum L.), a crop of global importance, is threatened by mixed viral infections, such as Potyvirus yituburosum (PVY) and Tobamovirus fructirugosum (ToBRFV). This study evaluated the antiviral potential of green-synthesized silver (Ag), silicon dioxide (SiO2), and cerium dioxide (CeO2) nanoparticles (NPs) against these viruses in seeds and seedlings. NPs were synthesized using aqueous walnut shell extracts. The nanoparticles were characterized by EDX and TEM. In two experimental phases, bell pepper seeds were treated with different concentrations of nanoparticles (50-1000 mg L-1) and subsequently exposed to PVY, ToBRFV, and both. Viral transmission was assessed by qELISA in seeds and seedlings. Seedling development, germination rates, and virus incidence were measured; phytotoxicity (CF50), antiviral efficacy (IC50/IC90), and the selectivity index (SI) were calculated. The results showed a significant reduction in viral load and inhibition of PVY and ToBRFV transmission in both single and mixed infections, especially at doses [≥]400 mg L-1. CeO2 nanoparticles exhibited the highest selectivity indices (SI > 3000) and no phytotoxicity. Ag and SiO2 nanoparticles also exhibited antiviral activity, but with slightly higher CF50 values. In the greenhouse, seedlings grown from seeds treated with nanoparticles showed a reduction in viral symptoms and an increase in SPAD index and height. In conclusion, bio-nanoparticles, especially CeO2, are promising antiviral agents against PVY and ToBRFV in pepper cultivation. Their high sensitivity and low toxicity make them good candidates for the sustainable management of plant viruses, justifying further field-scale evaluation.