l -Phenyllactic Acid–Mediated Suppression of Ralstonia pseudosolanacearum by Lactiplantibacillus plantarum from Fermented Agro-Waste

Bacterial wilt caused by Ralstonia pseudosolanacearum threatens global crop production. This study establishes Lactiplantibacillus plantarum MZ3, isolated from agricultural jiaosu, as an effective biocontrol and plant growth-promoting strain. MZ3 significantly reduced disease incidence in Nicotiana benthamiana 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 Ralstonia 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.