Includes bibliographical references.

Bacterial wilt of potato (Solanum tuberosum L.) caused by Ralstonia solanacearum Smith is difficult to management due to its soil-borne nature and has a wide host range. In the present study efficacy of two nanoparticles (NPs) viz., silver (Ag) and gold (Au) were tested both in vitro and in vivo against the R. solanacearum. In in vitro seven different doses were tested against the pathogen by disc diffusion method and result showed that, the effect was significantly dependant on the concentration of the NPs. The highest inhibition zone (mm) was recorded for AgNPs and AuNPs at 5000 ppm which was 1.70 mm and 1.45 mm respectively. Scanning Electron Microscope (SEM) analysis on action of AgNPs and AuNPs at 5000 ppm on bacterial cells depicts the distortion of the cell wall of NPs treated bacterial cell. ROS (reactive oxygen species) formation was more prominent in AgNPs and AuNPs treated bacterial cell. The effect of AgNPs and AuNPs was tested by seed treatment and soil application in both pot and field conditions observation on effect of NPs on plant growth parameters, seed germination percentage, and per cent disease incidence of potato plants were recorded with challenged inoculation of R. solanacearum. Results demonstrated that in pot condition, an increased plant height up to 43.83 cm as compared to control (37.37 cm) was recorded 60 days after sowing along with the per cent wilt disease reduction (70%) over control. In the AuNPs treated pot an yield of 2.5 kg per plant was recorded when AuNPs were used as treatment. Whereas in control an yield of 0.73 kg per plant was recorded. Similarly, in field conditions, an increased plant height up to 20.63 cm as compared to control (15.87 cm) was recorded at 60 days after sowing along with the per cent bacterial wilt disease incidence (29.63%). An yield of 4.72 kg per plot was recorded which was found much higher than the yield of control (2.92 kg per plot). The results obtained for the biochemical tests for the Ag and Au NPs treated plot at 5000 ppm resulted increase of TSS (187.41 ppm) for AgNPs, TSP (440.45 ppm) for control (with R. solanacearum), phenol (253.01 ppm) content for AgNPs, flavonoids (862 ppm) for both AgNPs, terpenoid (21.92 mg) for control (with R. solanacearum) and proline content (100.36 mg g-1) for AuNPs. Soil microbial population in Ag and Au NPs treated plot was found to be lowest in case of treatment with AgNPs at 5000 ppm, 3000 ppm and AuNPs at 5000 ppm. The present study showed encouraging result of using Ag and Au NPs as seed treating agent and soil drenching agent for the management of bacterial wilt of potato with enhance plant defence metabolite and yield.