Evaluation of inhibitory effects of extracts of plants from western Iran against 'Phytophthora' drechsleri

Crude aqueous and methanol extracts of 121 plant species from 41 families, collected from the west of Iran, were screened for antifungal activity against mycelial growth of Phytophthora drechsleri. The bioassay used was based on the paper disc diffusion method with four replicates. Extracts of 38 of 121 (about 31%) plant species had inhibitory activity against this phytopathogenic fungus, among which 23 species measurably inhibited the growth of Phytophthora drechsleri. A methanol extract of Xanthium strumarium had the strongest inhibitory activity (17.79+/-1.35 mm) against P. drechsleri followed by extracts of Glycyrrhiza glabra, Verbascum sp., Hypericum perforatum, Centaura depressa, Centaura sp., Lamium amplexicaule, Haplophyllum perforatum. An investigation of the efficacy of extracts of different plant parts on mycelial inhibition of P. drechsleri, using the paper disc method, indicated that the inflorescence and fruits of cocklebur (Xanthium strumarium) showed significantly more inhibitory effect than the other plant parts against the fungus. Two common species of cocklebur, X. strumarium and X. spinosa, grown around the city of Kermanshah, inhibited mycelial growth of the tested fungus, but extracts of X. strumarium had significantly more inhibitory effect against P. dreschleri than X. spinosa. The results of fractionation of leaf, fruit and inflorescence by thin layer chromatography (TLC) indicated that yellow and blue fractions (under UV) with relative fronts (Rf) equal to 0.93 and 0.98 of leaf, fruit and inflorescence fractions exhibited the highest inhibitory effect against P. dreschleri. These results suggest that cocklebur has potential for control of P. dreschleri and further green house and farm studies are recommended.