The Inhibitory Effects and Mechanisms of Carvacrol and Cinnamaldehyde Against Erwinia amylovora in Pears

ABSTRACT Erwinia amylovora is a phytopathogen and the primary causative agent of fire blight in pears, causing significant preharvest losses. The predominant method of controlling fire blight involves the application of agricultural antibiotics, which may promote the development of antimicrobial tolerance in E. amylovora populations. A novel approach to control fire blight disease was investigated using the natural products carvacrol, found in essential oils of various plants, and cinnamaldehyde, primarily found in the bark of cinnamon trees. This study determined that the minimum inhibitory concentrations (MICs) for carvacrol and cinnamaldehyde against E. amylovora were 100 and 250 μL/L, respectively. In a control test with detached pears, both carvacrol and cinnamaldehyde reduced the severity of fire blight on fruitlets. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) results validated the structural alterations and disturbances observed in E. amylovora biofilm upon treatment with carvacrol and cinnamaldehyde. Flow cytometry analysis revealed that carvacrol and cinnamaldehyde reduced the viability of E. amylovora cells, achieving reductions of 83.8% and 80.5% of their respective MICs. Moreover, reverse transcription‐quantitative PCR revealed a decrease in the expression of genes associated with motility, biofilm formation and the type III secretion system in E. amylovora following exposure to carvacrol and cinnamaldehyde. Carvacrol and cinnamaldehyde interfered with biofilm formation of E. amylovora , which decreased its infectivity and hence its virulence. This study reports that carvacrol and cinnamaldehyde are effective against fire blight control and prevention under laboratory conditions.