ANTIBACTERIAL IN VITRO ACTIVITY OF EXPERIMENTAL AND FORMULATED ESSENTIAL OILS TOWARDS ERWINIA AMYLOVORA

The control of Erwinia amylovora (Ea), causal agent of bacterial fire blight, is one of the major challenges in pome fruit production. Nowadays, the main control strategy of this disease is based on the use of integrated methods: the infections are mainly controlled through the use of chemical treatments, mainly based on heavy metals/antibiotic compounds and resistance inducers, and by biological control agents (BCA). Among BCA, antagonistic bacteria and natural compounds as essential oils/plant extracts were studied to find more ecofriendly control tools targeted to the control of Ea infections. In the present work, experimental and formulated essential oils were tested for their antimicrobial activity against Ea in in vitro experiments. The synergistic effect of the experimental oils was also evaluated by checkerboard assay, and the Fractional Inhibitory Concentration index was calculated; the synergistic effect of oil combinations was assayed by macro-dilution assay as well. Among the experimental oils tested, those of Origanum compactum and Satureja montana, carvacrol chemotyped (48.13% and 54.86%, respectively), and Thymus vulgaris, thymol chemotyped (46.84%), showed antibacterial activity; the minimal inhibitory concentration (MIC) resulted0.03% for all oils. VitiBioSap 458 Plus® and VitiBioSap ES Plus®, whose formulated oils mixture activity is enhanced by the presence of the MicroSap® component (Patent N° EP 3071039–28.09.2016), significantly reduced the Ea population after 24 h and resulted to be bactericidal at the concentrations 1% and 2%, respectively. Also Prevam Plus® (6%), an orange essential oil based compound, was shown to be able to inhibit the growth of Ea after 24h.