Antibacterial Effects of Several Plant Extracts and Essential Oils on Xanthomonas arboricola pv. juglandis in vitro

Walnut bacterial blight, caused by Xanthomonas arboricola pv. juglandis, is the most destructive bacterial disease of the genus Juglans worldwide. X. a. pv. juglandis bacterium has shown resistance to copper bactericides. Here with the aim of exploring some sources of natural bactericides for biocontrol of this bacterium, antibacterial activities of essential oils and aqueous extracts from 24 higher medicinal plant species were investigated, in vitro, on X. a. pv. juglandis. In diffusion assays, the majority of tested plant extracts and essential oils showed antibacterial activities against this bacterium. Significant antibacterial activities were observed for aqueous extracts of Allium sativum, Daturea stramonium, Rosmarinus officinalis, Peganum harmala, Ricinus communis, and Mentha piperita. Essential oils of Ziziphora persicae, Mentha piperita, Mentha spicata, and Achillea vermiculatus showed the highest antibacterial effects on X. a. pv. juglandis.