Biological control of Erwinia amylovora using essential oils-based products in vitro and in vivo

The spread of Erwinia amylovora (Ea) that causes fire blight, is still controlled by integrated preventive measures that include chemical compounds and antagonistic beneficial microorganisms. Plant essential oils (EO), natural antimicrobials, are increasingly considered as alternative tools in the defense of bacterial plant diseases. The efficacy of two EO-based products, VitiBioSap 458 Plus® (458) and VitiBioSap ES Plus® (ES) - containing among the components Cu++/Zn++ and the micro-clay MicroSap® -, and of Prevam Plus®(PP), based on sweet orange EO, was assayed in vitro and in vivo against Ea. In vitro, 458 and ES significantly reduced the Ea population and were bactericidal at 1 and 2%, respectively. PP inhibited the Ea growth at 6% but it was ineffective at 1%. In vivo, on pear detached flowers and fruitlets pre-treated with 458 (1-2%), ES (2-3%) or PP (6%) and inoculated with Ea, the disease incidence (DI) was determined. On apple detached flowers, pre-treated with ES or 458, the Ea population dynamic was evaluated up to 4 days and at each detection time the samples were observed at the scanning electron microscope. In ES- and 458-treated pear flowers, the DI was reduced to approx. 12-30% and 12-50%, respectively compared to the control samples treated with sterile distilled water (88-100%), while PP had no effect (85%). In pear fruitlets treated with ES or 458, the DI resulted between 12% and 46% respectively, lower than control. Furthermore, the Ea population was lowered in ES- and 458-treated apple flowers compared to the control samples.