Potassium phosphite and zinc oxide nanoparticles inhibit Ralstonia solanacearum growth, extracellular polysaccharide, and virulence in potato plants

Abstract Potassium phosphite (K-Phite) and zinc oxide nanoparticles (ZnONPs) were tested for their antibacterial activity against Ralstonia solanacearum on potato in vitro and in vivo. Treatments showed an inhibitory effect on bacterial growth and multiplication in a concentration-dependent manner in vitro, ZnONPs (8 mg/ml) and KP (0.01%) being the most effective, reducing bacterial growth by 88% and 63% and exopolysaccharide production by 99% and 87%, respectively. Scanning electron microscopy of treated bacterial cells revealed enlarged, misshapen, and wrinkled cell walls. As a result, all treatments significantly decreased the severity of potato wilt disease in vivo. The ability of these treatments to enhance potato plant resistance in the greenhouse was assessed through morphological traits, photosynthetic pigments, and antioxidant enzyme activity. The treatments promoted plant growth and increased tolerance to R. solanacearum infection, with the combined treatment showing the most notable effects. Total chlorophyll content significantly increased, and only the mixture treatment caused a significant change in carotenoids compared to the control. Assays of antioxidant enzymes (POD, SOD, APX, and CAT) indicated that K-Phite notably increased POD and CAT activity in root tissues in response to infection, while the mixture showed the strongest response. Therefore, K-Phite and ZnONPs may serve as bacterial EPS inhibitors, enhance plant growth, and bolster defense mechanisms against R. solanacearum in potato. Additionally, FTIR analysis was performed to monitor chemical changes, supporting the evidence of reduced EPS production. EPS levels were also examined by measuring hexosamine content using the Elson-Morgan method, and the results were consistent with previous findings: a significant decrease in EPS after treatment. Taken together, these results indicate the performance of K-Phite and ZnONPs in inhibiting bacterial EPS, promoting healthy growth, and strengthening potato defenses against R. solanacearum.