Antibacterial activities of essential oils extracted from medicinal plants against seed-borne bacterial disease agent, Acidovorax avenae subsp. citrulli

摘要

Antibacterial properties of essential oils derived from several plant species belonging to Lamiaceae family such as thyme (Thymbra spicata L. subsp. spicata and ThymusserpyllumL.), origanum (OriganummajoranaL.), mint (MenthaspicataL.), lavender (Lavandula stoechas L. subsp. stoechas), lemon balm (Melissa officinalis L.), rosemary (Rosmarinus officinalis L.) and basil (Ocimum basilicum L.) were investigated against seed-borne plant pathogenic bacterium, Acidovorax avenae subsp. citrulli (Aac), causalagent of bacterial fruit blotch of watermelon. By using paper disc diffusion assay, the most effective essential oil caused by T. spicata was followed by essential oils obtained from T. serpyllum, O. marjarom, M. spicata, M. officinalis, R. officinalis,L. stoechas and S. officinalis, respectively. By using micro agar broth dilution assay, minimum bactericidal concentrations of the essential oil varied from 6 to 40 mg/ml, depending on the plant species. The lowest and highest EC_(50) values were recorded for thyme (1.98 mg/ml) and lavender (15.42 mg/ml) essential oils, respectively. Laboratory screenings of plant extracts have given encouraging results, indicating their potential use in the management of diseases caused by Aac. As the bacterial agent known to be transmitted through seeds, one of the ways of application of the plant essential oil is as a seed treatment. Thyme and origanum essential oils appear to be promising in this respect. Further study is underway in our laboratory to screen for their efficacy in managing other seed-borne bacterial disease agents in different commercially important crops.