Methyleugenol from <i>Melaleuca bracteata</i> essential oil attenuates the virulence of <i>Dickeya fangzhongdai</i> Onc5

The <i>Dickeya</i> 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 <i>Melaleuca bracteata</i> essential oil. Treatment with <i>M. bracteata</i> EO and ME at 10‰ and 5‰ (sub-minimal inhibitory concentration, sub-MIC) resulted in a dose-dependent reduction (<i>p</i> < 0.05) in the secretion of plant cell wall degrading enzymes (PCWDEs), without inhibiting growth. Exposure of <i>D. fangzhongdai</i> 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 <i>vfmH, vfmI vfmA</i>, <i>vfmK</i> and <i>vfmE</i>. The expression of PCWDEs genes was also reduced. Collectively, the results support a mechanism by which <i>M. bracteata</i> EO and ME interfere with <i>D. fangzhongdai</i> Onc5 virulence <i>via</i> the Vfm-QS machinery.