<scp>l</scp> -Phenyllactic Acid–Mediated Suppression of <i>Ralstonia pseudosolanacearum</i> by <i>Lactiplantibacillus plantarum</i> from Fermented Agro-Waste

Bacterial wilt caused by <i>Ralstonia pseudosolanacearum</i> threatens global crop production. This study establishes <i>Lactiplantibacillus plantarum</i> MZ3, isolated from agricultural jiaosu, as an effective biocontrol and plant growth-promoting strain. MZ3 significantly reduced disease incidence in <i>Nicotiana benthamiana</i> while enhancing biomass and chlorophyll content. Cell-free culture filtrate assays showed that antagonism was primarily mediated by organic acids, as activity persisted after heat, proteinase-K, and catalase treatments but was eliminated upon pH neutralization. UHPLC-HRMS profiling revealed an organic-acid-rich metabolome dominated by L-3-phenyllactic acid (PLA), which exhibited strong inhibitory activity in purified form. Scanning electron microscopy confirmed membrane damage in treated <i>Ralstonia</i> cells. VOCs from strain MZ3 also suppressed pathogen growth, with SPME-GC-MS identifying 22 compounds, including 2-heptanone and benzaldehyde. Genomic analysis supported biosynthetic pathways for key metabolites. Strain MZ3 further enhanced SOD, POD, and CAT activities and exhibited PGP traits, supporting its potential application as a biologically derived agent for managing bacterial wilt.