Biopolymer Coated with ZnO Nanoparticles: Synthesis, Antiphytopathogenic Activity, and Effects On Tomato Growth and Bacterial Speck Disease Control

This study aimed to examine the protective effects of a new biopolymer Cls-Alg@ZnO, composed of ZnO nanoparticles, cellulose, and alginate, on the growth and immunity of tomato plants in controlling bacterial speck disease caused by Pseudomonas syringae pv. tomato. Additionally, its antimicrobial activity was assessed against various cryptogams, including Alternaria solani, Cladosporium fulvum, Fusarium oxysporum f. sp. lycopersici, F. oxysporum f. sp. dianthi, F. oxysporum f. sp. melonis, Stemphylium sp., and Verticillium dahliae. The results revealed that Cls-Alg@ZnO (300 mu g mL-1) drastically reduced the mycelial growth of F.o. lycopersici, F.o. dianthi, Stemphylium sp., and V. dahliae by more than 70%. Cls-Alg@ZnO caused only slight inhibition of the radial growth of F.o. melonis and C. fulvum; however, it inhibited sporulation by 49% and 59%, respectively. When sprayed at 150 mu g mL-1 on tomato plants in the greenhouse, the biopolymer did not affect stem growth but significantly enhanced leaf biomass and improved net photosynthesis, stomatal conductance, transpiration rate, and Nitrate reductase activity. Furthermore, the biopolymer demonstrated the potential to inhibit the growth of P.s. tomato in planta. The number of leaf lesions and the severity of the disease were reduced by 68% and 34%, respectively, and these reductions were correlated with a significant decrease in the bacterial population in planta. Cls-Alg@ZnO did not affect the accumulation of H2O2 or lipid peroxidation induced by P.s. tomato. However, it promoted the activity of antioxidant enzymes, such as Ascorbate peroxidase and Guaiacol peroxidase. Our results suggest that this new biopolymer may be an effective biopesticide for plant protection.