This study was aimed to investigate the antifungal effect of the crude extracts derived from 37 Iranian plant species against Phytophthora melonis and Pythium aphanidermatum, the causal agents of cucumber root rot and damping off. The crude extracts were obtained using three different solvents; ethanol, methanol and water. The inhibitory effect of these extracts was examined based on the paper disc diffusion method (5 mg per paper disc) with four replications. The ethanolic extract of Acroptilon repens, that showed a remarkable inhibitory effect on the tested oomycetes was selected for further examination. To determine the most effective component, the ethanolic extract of A. repens was fractionated by thin layer chromatography (TLC) and each fraction was tested for the antifungal activity. The potential of the ethanolic extract of A. repens in the control of cucumber damping off agents was evaluated in a completely randomized design with eight replications, under greenhouse conditions. Based on the results obtained from the screening of TLC fractions, it was found that a fraction with Rf value equal to 0.89 had the most inhibitory effect against the tested oomycetes. Greenhouse experiment showed that the soil treatment by the ethanolic extract of A. repens at all the selected concentrations (0.2, 0.4 and 0.6 g per plastic pot) were significantly effective in reducing the disease incidence caused by P. melonis compared to the control. Moreover, seed treatment by 10% w/w of ethanolic extract of A. repens significantly suppressed damping off symptom caused by P. aphanidermatum, when compared to the control.
