Medicinal plants are potential sources of antimicrobial compounds, which could be used in the management of plant diseases. Research on plant extracts and essential oils which may substitute the use of agrochemical or which may contributes to the development of new compounds is extremely important. Essential oils are promising alternative compounds which have an inhibitory activity on the growth of pathogens. Application of essential oils is a very attractive method for controlling plant diseases. The Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici can be prevented through growing resistant tomato cultivars and soil disinfection by some chemicals. Recently the essential oils as a new method and replace for the control of plant diseases have been accepted. In this study the effect of essential oil of Thymus vulgaris was prepared by using a Clevenger apparatus and its antifungal effect on Fusarium oxysporum f. sp. lycopersici was investigated in the laboratory based on mixing essential oil with medium with four replicates. Evaluation of essential oil antifungal was tested at different concentrations of essential oils (i.e. 0-1000 ppm). Growth rate decreases with increasing concentration. No growth was observed at concentrations of more than 1000ppm. In section survey of enzyme activity, the essential oil reduces cellulase activity but over time, the effect of essential oil decreased. The results of this evaluation of indicate that compounds found in essential oil to reduce fungal growth and enzyme activity. Considering that the production of cellulase enzyme is one of the most important mechanisms influencing penetration to the host, thus reducing the amount of secreted enzymes indicates effect of essential oil on the pathogenic mechanisms and production of cellulase gene expression. These results indicate that essential oils after suitable formulation could be used for the control of Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici pathogens.

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