Aspergillus niger Mediated Biosynthesis of Bimetallic Copper–Selenium Nanoparticles and Their Roles in Enhancing Resistance to Ralstonia solanacearum

Bacterial wilt in Solanum melongen is caused by the destructive soil-borne bacterial pathogen Ralstonia solanacearum, which is characterized by a wide host range, soil persistence, and significant yield losses. This study explores the characterization and antibacterial effectiveness of bimetallic copper–selenium nanoparticles (Cu-Se-NPs) synthesized using Aspergillus niger, focusing on their role in enhancing systemic resistance in Solanum melongena against R. solanacearum. FTIR and XRD confirmed the successful biosynthesis of Cu-Se-NPs, displaying characteristic peaks and a crystalline structure. DLS revealed an NP size of 25 nm, with a polydispersity index of 0.18 and an average zeta potential of −31 mV, indicating good stability. Antibacterial assays showed that Cu-Se-NPs effectively inhibited R. solanacearum, achieving a minimum inhibitory concentration (MIC) of 12.5 µg/mL, surpassing the effects of Na₂SeO₃ and Cu(CH₃COO)₂. Treatment with Cu-Se-NPs resulted in a 27.5% reduction in the disease index (DI), enhancing plant protection by 67.6%. Additionally, these NPs positively affected photosynthetic pigments, increasing chlorophyll and carotenoid levels while elevating total phenol and free proline content in infected plants. The activity of antioxidant enzymes increased significantly, indicating enhanced stress tolerance. These findings indicate the potential of Cu-Se-NPs as a novel biopesticide and nanofertilizer, promoting plant health and resilience against bacterial pathogens.