The experiment was conducted during 2015 to Green synthesis of silver nanoparticles using Grapefruit's peel extract. In addition, we find out the effect of silver nanoparticles on dampingoff caused by Rhizoctonia solani in cucumber plants. The silver nanoparticles characterized for their size and shape using scanning electron microscopy and transmission electron microscopy(TEM), respectively. X-ray diffraction spectroscopies (XRD) were evaluated to determine the concentration of metal ions. Results showed that the size of nanoparticle was 5-65 nm and the average size was determined 55.02 nm with shape of spherical. In addition, the impact of silver nanoparticles was investigated by Grapefruit's peel on response of cucumber plants inoculated with Rhizoctonia solani.Variables analyzed were superoxide dismutase (SOD) activity, fresh and dry weight of root and shoot. The data analysis revealed that fresh and dry weights of roots and shoots were significantly higher in treatments containing 30, 50 and 70 grL -1 of nanoparticles compared to the control plants (P<0.01). The highest superoxide dismutase activity was observed in 70 grL -1 nanoparticles treatment after 48 hours. however, a significantly higher percentage of disease damage was appeared in control plant, while symptoms were observed in treated plants with nanosilver. The results of this study suggest that enhancement of defense enzyme.

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