Salicylic acid-functionalized nanogels enhance tobacco mosaic virus resistance and alleviate oxidative stress in crops

Tobacco mosaic virus (TMV), one of the most devastating plant pathogens worldwide, causes catastrophic agricultural losses. While chemical pesticides remain primary method for controlling viral diseases, their improper use poses significant ecological risks, including environmental persistence and biomagnification. Herein, we employed a nanogel carrier to encapsulate salicylic acid (SA), creating a green nanobiostimulant termed salicylic acid-functionalized nanogels (SAN). This SAN exhibited excellent stability, strong foliar adhesion, a favorable slow-release profile, and high biosafety for tadpoles. Foliar application of 50 mg/L SAN resulted in a higher control efficiency against TMV in tobacco (Nicotiana tabacum L.) plants than that of SA or lentinan (LNT, a commercial biostimulant) alone, and the disease severity of SAN was significantly reduced by 29.6 % and 20.5 % compared with SA and LNT, respectively. Mechanistically, 50 mg/L SAN directly inactivated TMV by causing the aggregation and fracture of TMV particles. Furthermore, SAN indirectly induced tobacco plant resistance to TMV via activating endogenous signaling (Ca^2 + influx and phytohormone accumulation), upregulating the expression of key genes for disease resistance (e.g., PR1, PR3), and enhancing defense metabolites involved phenylpropanoid pathway (e.g., chlorogenic acid, ferulic acid, rutin). Moreover, SAN significantly mitigated tobacco leaf oxidative stress by increasing the activity of antioxidant enzymes (SOD, POD, CAT) and the production of flavonoids, and such effect was better than that of SA and LNT. Overall, SAN is a promising eco-friendly nanobiostimulant with the potential to replace conventional biostimulants and pesticides for sustainable disease control in agroecosystems.