The use of natural compounds due to their antifungal, antibacterial and antioxidant properties is proceeding in control of plant diseases. Tobaccosore shin of pathogen fungiare important phytopathogens distributed worldwide and can cause yield losses in tobacco growing countries. The use of plant extracts for management of this disease is preferable because pesticides are expensive and may pollute the environment.This design investigated the inhibitory effects of some medicinal plant extracts on growth of Rhizoctonia solani the cause of tobacco sore shin and selection of a suitable solvent for extraction is performed in the laboratory. In this study, crude extracts of 3 plant species were tested in vitro for antifungal activity against R. solani. The plant were extracted with water, acetone, hexzan and methanol were carried out in facturial with three factors including:crude extracts (3 plant species) and solvent (4 solvent) and 6 cocentration (0, 250, 500, 1000, 2000 and 4000 ppm) based on Completely Randomized Design with 3 replications in Tirtash Research and Education Center in 2017. The minimum inhibitory concentration of each extracts was determined by agar diffusion method. Results indicated that crude extracts of lemon verbena and nettle have remarkable antifungal activity. methanol were the best solvent to extract antifungal compounds.By increasing the concentrations of plant extracts, inhibitory effect on mycellium growth of R. solaniagainsttobacco sore shin increased.
Methanol extracte of lemon verbenain concentrations of1000, 2000 and 4000 ppm and hexane extract of lemon verbena with concentration of 2000 and 4000 ppm and also asetone extracteof with concentration of 2000 lemon verbenahighest inhibitory effect of mycelial growth was 88.8%, 92.5%, 96.2%, 88.8%, 92.5%, and 88.8%, respectively.The resultsshowedthehigh potential of theextracts of lemon verbena and nettlewhich could be used as a thebiological product againsttobacco sore shin