Effectiveness of Plant Essential Oils Against Erwinia Amylovora, Pseudomonas Syringae pv. Syringae and Associated Saprophytic Bacteria on/in Host Plants

Abstract

Plant essential oils of five aromatic herb species of the family Lamiaceae (Origanum sp., Thymus sp., Mellisa sp., Mentha sp. and Nepeta sp.) were investigated for antimicrobial effect against plant pathogenic (Erwinia amylovora and Pseudomonas syringae pv. syringae) and saprophytic (Pseudomonas fluorescens, Pantoea dispersa and P. agglomerans) bacteria commonly associated with both pathogens in plant tissue of healthy and/or diseased fruit trees in orchards. The screening was carried out in vitro on agar plates seeded with the target organism. All screened essential oils exhibited a higher level of antibacterial activity than streptomycin used as a standard in all tests. Plant essential oils from Origanum compactum, O. vulgare and Thymus vulgaris were significantly more effective against all tested bacteria than essential oils from Mellisa officinalis, Mentha arvensis and Nepeta cataria. The main compounds of essential oils from O. compactum, O. vulgare and T. vulgaris were carvacrol and thymol. Apart from the three above most effective oils, those from Nepeta cataria and Mentha arvensis were also effective against E. amylovora, and M. officinalis and M. arvensis against P. syringae. pv. syringae, however only M. officinalis was effective against P. fluorescens. All tested herb essential oils exhibited the highest antimicrobial activity against P. agglomerans and the lowest inhibitory activity against P. dispersa.