Phytophthora species are soilborne oomycete that can infect more than 45 species of crops plants and survives in the soils as Oospores for several years [1, 2]. This pathogen can cause fruit, crown, and root rot, and stem and leaf blight disease. It is one of the most devastating diseases affecting cucurbit and vegetables production in Iran [3]. In this study we survey the antifungal activity of Thymus eriocalyx essential oil and Metalaxyl fungicides against three species of Phytophthora including P. capsici, P. drechsleri and P. melonis causal agent damping-off in plants of Pepper, Cucumber and Melon in vitro respectively. Six different concentrations of essential oils and fungicide were used for assessment of their inhibitory activities against the pathogen through mycelial growth inhibition on Corn Meal Agar. Fungal radial growth was measured and a median effective concentration (EC50) value (ppm) was calculated according to the linear relation between inhibitory probit and concentration logarithm. The chemical composition of the essential oils was determined by gas chromatography-mass spectrometry (GC-MS). Also, Data were analyzed using SPSS software. The results showed that Thymus eriocalyx essential oil were very effective on three species of Phythophthora. Maximum and minimum EC50 values of oil on species of Phythophthora were 41.060 and 28.494 for P. capsici and P. melonis respectively. The mean EC50 values for Metalaxyl on P. capsici, P. drechsleri and P. melonis were 20.869, 20.055 and 17.702, respectively. The profile of the oil components of T. eriocalyx showed that Thymol (35.86%), Eucalyptol (7.74%), Borenol (7.95%), γ-Terpinene (5.49%) were the main compounds. Nevertheless, the effectiveness of the essential oils was variable depending to concentration of plant essential oil and species of fungi. This results show that essential oil may be have potential to control of some Phytophthora species and could be considered for developing new fungicides.
