Synthesis of silver nanoparticles using extract of Ocimum kilimandscharicum and its antimicrobial activity against plant pathogens

Biological synthesis of silver nanoparticles using plants is gaining importance as an economically viable and ecofriendly approach. The present study reports synthesis of silver nanoparticles using an important Himalayan medicinal herbal plant Ocimum kilimandscharicum and the potential of biosynthesized silver nanoparticles for control of plant pathogens. The reducing effect of the aqueous plant extract for synthesis of silver nanoparticles was investigated at different concentrations and temperatures. UV-visible absorption spectrum recorded for samples prepared with different concentrations (20, 30, 40 and 50% v/v) of plant extract and treated at different temperatures (40, 60, 80 degrees C and room temperature) confirmed the formation of silver nanoparticles. Antimicrobial activity of the silver nanoparticles was tested against Fusarium oxysporum, Colletotrichum gloeosporioides, Bacillus sp. and Enterobacter cloacae. Complete inhibition of F. oxysporum was observed at 75 ppm concentration of silver nanoparticles as compared to 67.75 +/- 1.15 mm radial growth without silver nanoparticles after 7 days of incubation. No growth of C. gloeosporioides was observed in vitro at 100 ppm silver nanoparticles as compared to 44.50 +/- 1.14 mm radial growth in the absence of the silver nanoparticles. Inhibitory effect of biosynthesized silver nanoparticles was also observed against bacterial pathogens. The highest inhibition zone of 14.5 +/- 1.11 mm was observed against E. cloacae with 100 ppm silver nanoparticles. The obtained results confirm strong antimicrobial activity of the silver nanoparticles synthesized using O. kilimandscharicum against plant pathogens.