In vivo antibacterial activity of two essential oil based products to control fire blight

The products VitiBioSap 458 Plus® (VBS458) and VitiBioSap ES Plus® (VBSES) based on essential oil mixture, Cu++ (3.5%), Zn++ (1%) and the MicroSap® component (Patent N°EP3071039–28.09.2016), were assayed in vivo against Erwinia amylovora (Ea),the etiological agent of the bacterial fire blight. Detached flowers andimmature fruitlets of pear were pre-treated with VBS458 (1-2%) or VBSES (2-3%), and inoculated with an Ea aqueous suspension (ca. 106 CFU/ml); the disease incidence was evaluated within 6 days after the inoculation. Moreover, the population dynamics of an Ea rifampicin resistant mutant strain (Ea 273R1) was evaluated up to 4 days on detached apple flowers, pre-treated with the above products. In addition, at each detection time, the flowers were fixed in 5% glutaraldehyde solution, dehydrated in ethanol and processed by Critical Point Dryer. The samples, after gold sputter coating, were observed by Philips SEM 515 scanning electron microscope at 20kV. Sterile distilled water (SDW) and streptomycin sulphate (STR) were used as negative and positive controls, respectively. In VBSES- and VBS458-treated pear flowers, the disease incidence was significantly reduced (12-30% and 12-50%, respectively) compared to that detected in SDW-treated flowers (88-100%). In pear fruitlets treated with the products, the disease incidence resulted between 19% and 46%, similar to that on STR-treated pears (30%). Furthermore, the Ea population was significantly lowered in VBSES- and VBS458-treated apple flowers, in comparison to that of SDW-treated control samples.