Methyleugenol from Melaleuca bracteata essential oil attenuates the virulence of Dickeya fangzhongdai Onc5

The Dickeya species cause maceration-associated diseases, which harm numerous crops and ornamental plants. In presence study, anti-quorum sensing active compound, methyleugenol (ME), was firstly isolated and identified from Melaleuca bracteata essential oil. Treatment with M. bracteata EO and ME at 10‰ and 5‰ (sub-minimal inhibitory concentration, sub-MIC) resulted in a dose-dependent reduction (p < 0.05) in the secretion of plant cell wall degrading enzymes (PCWDEs), without inhibiting growth. Exposure of D. fangzhongdai Onc5 to EO and ME significantly reduced its virulence and infection capability in the tested hosts, including: potatoes, cabbages and carrots. The exposure of bacteria to EO and ME mainly inhibited the expression of Vfm-QS genes, including vfmH, vfmI vfmA, vfmK and vfmE. The expression of PCWDEs genes was also reduced. Collectively, the results support a mechanism by which M. bracteata EO and ME interfere with D. fangzhongdai Onc5 virulence via the Vfm-QS machinery.