Effects of plant essential oils on growth and virulence factors of Erwinia amylovora

Erwinia amylovora causes fire blight in plants of economic importance in Rosaceae family. In this study, 11 essential oils were screened for their antibacterial activities and capabilities to influence the growth and virulence factors by the E. amylovora, such as amylovoran production, biofilm formation, and motility at non-lethal concentrations. Essential oils from Foeniculum vulgare and Pimpinella anisum showed strong antibacterial activity, those of Artemisia aucheri and Heracleum persicum had a moderate antibacterial activity. Oils of seven other plant species did not show substantial growth inhibition but could reduce the production of virulence factors in E. amylovora at non-lethal concentrations. Determining bacteriostatic and bactericidal concentrations enabled us to gather precise data about the antibacterial characteristics. The results suggested that at non-lethal concentrations, some essential oils reduced the effect of virulence factors of E. amylovora. An inverse correlation was found between amylovoran and biofilm production when the bacterium was treated with oils of H. persicum, P. anisum, C. arabica, J. horizentalis, C. aurantifolia and V. agnus-castus. The oils with low antibacterial activity had an insignificant effect on motility at non-lethal concentrations. Generally, Apium graveolens (celery seed) and Curcuma longa (turmeric) essential oils showed the optimum reduction in the effects of virulence factors of E. amylovora. These oils led to 41.71% and 30.17% reduction in the disease progression of E. amylovora on immature pear fruit, respectively and reduced disease progression in the shoot of pear seedlings with 26.9% and 16.7%. This study indicated that essential oils individually may be applied as environmentally safe compounds for controlling the fire blight disease.