Fermented chrysanthemum stem as a source of natural phenolic compounds to alleviate tomato bacterial wilt disease

Natural antimicrobial compounds (NACs) in the plant stem are crucial for replacing conventional synthetic pesticides in the control of soil-borne diseases, and microbial fermentation can enhance their concentration and bioactivity. In this study, the stems of 10 plant species were collected for fermentation by probiotic bacteria <i>Bacillus amyloliquefaciens</i> T-5 to identify the most effective plant resource for controlling tomato bacterial wilt disease and discover key NACs. Chrysanthemum stem was identified as an optimal fermentation substrate, as its water-soluble extracts (WSEs) significantly inhibited the growth of pathogenic <i>Ralstonia solanacearum</i> and effectively alleviated tomato wilt under greenhouse conditions. Key metabolites, primarily phenolic acids including 2-hydroxy-3-phenylpropanoic acid (PLA), 3-(4-hydroxyphenyl)-propionic acid (HPPA), and mandelic acid (MA), were determined by metabolomics, all of which significantly inhibited the growth of <i>R. solanacearum</i> at a concentration of 0.2 mM, with only HPPA effectively controlling tomato wilt. Thus, fermented chrysanthemum stem contains NACs that are effective against bacterial wilt, providing a green option for controlling soil-borne diseases.