Antibacterial Activity of Ferulic Acid Ester against Ralstonia solanacearum and Its Synergy with Essential Oils

Ralstonia solanacearum is one of the ten most harmful plant bacteria worldwide, and traditional agrochemicals are not very effective in controlling this pathogen. Moreover, excessive pesticides always bring organic residues and resistant strains, which cause the unsustainability of the environment. In this paper, ferulic acid and essential oils are used as antibacterial materials. These compounds are natural substances with low toxicity and environmental safety. Through the structural optimization and the analysis of binary combined bacteriostatic efficiency, the MIC values of chlorobutyl ferulate (2e) and peppermint essential oil (EO1) were 0.64 mg/mL and 2.02 mg/mL, respectively, and the MIC value of 2e-EO1 (mass ratio 1:1.5) was 0.40 mg/mL. The growth rate of bacteria treated with 2e-EO1 was inhibited, the OD590nm value of cell membrane decreased by 57.83%, and the expression levels of hrpB, pehC, pilT, polA, aceE, egl, and phcA were downregulated to 18.81%, 30.50%, 14.00%, 44.90%, 86.79%, 23.90%, and 27.56%, respectively. The results showed that 2e-EO1 had a synergistic inhibitory effect against R. solanacearum. It significantly affected the formation of the bacterial cell membrane and the expression of pathogenic genes. Consequently, 2e-EO1 provides the potential to become a green pesticide and can promote the sustainability of the agricultural ecological environment.