Chitosan nanocarriers loaded with salicylic acid for controlling fall armyworm (Spodoptera frugiperda) and alleviating oxidative stress in maize plants

Nanotechnology employing nanostructured materials is becoming a promising and green tool for crop protection against abiotic and biotic stresses. As eco-friendly biostimulants, chitosan (CS) and salicylic acid (SA) could induce plant resistance to insect herbivores. However, to date, the control efficiency of the SA-CS nanocomposites (SCNs) on insect herbivores and their underlying mechanism of activating plant defense against herbivores are still unclear. Herein, 17.2 nm of SCNs with excellent stability were prepared to control fall armyworm (Spodoptera frugiperda) on maize plants. We found that foliar application of SCNs (100-1000 mg L-1) exhibited higher control efficiency for S. frugiperda than SA and CS treatment alone, and 100 mg L-1 SCNs significantly decreased the growth of S. frugiperda by 54.7% as compared to the control. Mechanistically, SCNs enhanced maize plant resistance to S. frugiperda via increasing the leaf defense compound benzoxazinoid (e.g., DIMBOA-Glc, DIBOA-Glc, DIBOA, DIMBOA, DIM(2)BOA-Glc, HDM(2)BOA-Glc and MBOA) contents by 36.7-179.8%, and the expression of anti-insect genes (e.g., JAC1, Pep1, JAR1a, RIP2, MPI) by 2-19 fold. Additionally, SCNs increased activities of leaf antioxidant enzymes (SOD, POD, CAT) compared to CS and SA treatments, thus decreasing leaf oxidative stress caused by S. frugiperda attack. Altogether, SCNs could act as an eco-friendly nano-biostimulant for green pest control in agroecosystems.