حمیدرضا علیزاده

Cucurbit downy mildew caused by Pseudoperonospora cubensis is one of the most important foliar diseases of cucurbits causing significant yield losses in the world. Chemical control is not always feasible because of the high costs associated with fungicides, their application, and side effect on human and nature. Systemic acquired resistance (SAR) is known to play an important role in plant diseases and pest resistance. Benzothiadiazole (BTH) is an effective in vitro and acts via inducing natural defense mechanisms in plants. It was used in this study for inducing resistance against downy mildew of cucumber. Seven-day-old seedling (Superdaminos cultivar) were transferred to potting soil, kept at 25 °C 16 hours photoperiod and at a relative humidity (RH) of 70%. Seedling at the tree-to four- leaves stage inoculated with BTH at concentration of 0.01, 0.02, 0.04 mg/ml. for inoculation four holes were punched in to the soil around the base of seedling in each pot. Different concentrations of BTH solution were poured in to the holes. Plant were kept in greenhouse condition for two days. Then three Leaves of each plant were detached and inoculated with pathogen. The inoculated leaves were kept in plastic box with 22°C and 90 percent relative humidity. For preparing of P. cubensis inoculum leaves with symptoms of disease were collected from disease nursery and kept in the dark place at 100% RH overnight for producing of sporangia. Sporangia were collected from the lower side of leaves using a brush and suspended in sterilized water. The concentration of sporangia adjusted to 5×10 4 sporangia per milliliter using a hemacytometer. Seven days after inoculation of leaves the disease were evaluated by scoring the infected leaves using six scores (0, 1, 3, 5, 7, 9) according the number and extension of lesions on leaves. Results showed that the disease index were 55, 40, 27 in concentration of 0.01, 0.02, 0.04 mg/ml respectively. Statistically analyses of data showed the ). The b