Antibacterial activity of the essential oil and extracts of Satureja hortensis against plant pathogenic bacteria and their potential use as seed disinfectants

The aim of this study was to determine the antibacterial activity and potential use as seed disinfectant of Satureja hortensis L. essential oil, extracts (n-hexane, chloroform, acetone and methanol) and two pure compounds (carvacrol and thymol) against plant pathogenic bacteria. Antibacterial activity assays were carried out by disc diffusion method. Minimum inhibition concentrations (MICs) were determined by a twofold serial dilution method. The seeds were exposured to the essential oil vapors or directly soaked in the essential oil and extracts (hexane, methanol and hexane-methanol extracts mixture) suspensions at different concentrations. They were tested for their effectiveness on the percentage of the germinated seeds (tomato and/or lettuce) coated with some bacteria (Clavibacter michiganensis ssp. michiganensis, Xanthomonas axanopodis pv. vesicatoria and/or Xanthomonas axanopodis pv. vitians), the number of the infected seedling, disease severity and/or plant shoots and roots fresh weights in Petri plate or pot assays. Our results showed that the essential oil, carvacrol and thymol have a strong antibacterial activity against bacteria on Petri plates. However, the extracts showed weak antibacterial activity. The direct application of the some essential oil concentrations showed toxic effect on seed germination. On the other hand, the indirect application of the essential oil, direct or indirect applications of the hexane and methanol extracts were not toxic. The best successful result was obtained from 2.5 mg/ml concentration of hexane-methanol extract mixtures applications for lettuce seeds, infected with X. axanopodis pv. vitians. In this application, the disease severity rate was minimum level, and germination rate, shoots and roots fresh weights were maximum level. Our results show that hexane-methanol extract mixture of S. hortensis can be used as a seed disinfectant and as a botanical pesticide for management of plant bacterial disease. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.