اثر چند قارچکش شیمیایی در بازدارندگی از رشد رویشی قارچ Sclerotium rolfsii عامل بیماری پوسیدگی ساقه بادام زمینی در شرایط آزمایشگاه

Sclerotium rolfsii fungus is one of the important pathogens of peanut, which causes a quantitative and qualitative decrease in the yield of this product in Guilan province. This fungus is considered to be the cause of the white rot disease of peanut stem, and the management of this disease is very necessary to increase the production and yield of peanut. One of the most important strategies for disease management is seed disinfection with chemical fungicides. This research was conducted in order to investigate the effect of some chemical compounds in inhibiting the mycelial growth of S. rolfsii in laboratory conditions. For this purpose, sampling was done from peanut plants with symptoms of white stem rot disease in Astaneh-Ashrafiyeh county. The samples collected from infected plant organs were placed in plastic bags and transported to the laboratory. After surface disinfection with 5% sodium hypochlorite, pieces of root and stem tissue with disease symptoms were placed on potato-dextrose-agar (PDA) culture medium in Petri dishes and kept at 25 degrees Celsius for three days. After isolating the fungal isolates, they were purified by the tip culture method. To carry out the pathogenicity test, the seeds of peanut variety NC2 were planted in plastic pots with an opening diameter of 10 cm containing sterile light soil. Mycelium and sclerotium of the pathogenic isolate were inoculated in the collar area of 30-day-old peanut seedlings and the inoculated seedlings were kept in the greenhouse at a temperature of 25±2 degrees Celsius and a relative humidity of 70%. Seven days after inoculation, symptoms of browning and rotting of root and stem were examined and the pathogen was isolated again. In addition, the efficacy the chemical fungicides Thiophanate-methyl (Topsin M WP 70%), Captan (Captan WP 50%), Tebuconazole (Raxil DS 2%), Difenoconazole(Dividend DS 3%, Triticonazole + Pyraclostrobin (Insure Perform FS 12%), Metalaxyl M+Fludioxonil (Maxim XL FS 3.5%) and Metalaxyl-Mancozeb (Downy G WP72%)were tested in inhibiting the mycelial growth of S. rolfsii on PDA medium. The fungus was grown on PDA for seven days. The investigated fungicides were added to the PDA medium in the same concentrations or more or less than the recommended concentrations of the manufacturing companies, and in the control Petri dish, the medium without fungicide was used. Then, the Petri dishes were kept at 25 °C and the diameter of the colonies was measured daily for seven days. Comparison of the inhibition rate of S. rolfsii mycelial growth by different concentrations of chemicals showed that Downy‌ G WP72%, 1250 ppm Insure Perform, 600 ppm and Raxil DS 2%, 600 ppm had the highest inhibition rate of fungus vegetative growth, and Topsin M WP 70%, 2500 ppm showed the lowest inhibition rate.