Antagonistic activity and biocontrol potential of Pseudomonas sp. T19G isolated from the tomato rhizosphere against Ralstonia solanacearum.

Tomato bacterial wilt, caused by the soilborne bacterium Ralstonia solanacearum, remains difficult to manage, creating a need for biologically derived control agents. Here, we isolated Pseudomonas sp. T19G from the rhizosphere soil of healthy tomato plants and evaluated its antagonistic activity, protective effects, genomic basis, and influence on rhizosphere function. T19G fermentation broth inhibited R. solanacearum, and sterile cell-free supernatant caused a dose-dependent decline in viable pathogen populations. T19G significantly reduced viable root-associated pathogen populations and pathogen gene copy numbers, alleviated infection-induced growth suppression, partially restored leaf chlorophyll levels, and mitigated the increases in root catalase and superoxide dismutase activities. Whole-genome sequencing revealed a 6.43-Mb chromosome, and genome mining identified two putative bacteriocin genes, bct1779 and bct5326. Purified Bct1779 and Bct5326 inhibited the growth of R. solanacearum in a concentration-dependent manner, achieving inhibition rates of 73.64% and 56.54% at 80 μg/mL, respectively. DIA-MS confirmed the accumulation of the corresponding recombinant proteins in transgenic tomato roots, and aqueous root extracts from both transgenic lines inhibited R. solanacearum. Following pathogen challenge, the transgenic lines exhibited lower root pathogen loads, reduced disease indices and AUDPC values, and better-maintained plant growth than infected wild-type plants. T19G pretreatment also mitigated selected pathogen-induced nutrient disturbances and restored rhizosphere phosphatase, catalase, and dehydrogenase activities. Collectively, T19G combines extracellular antibiosis with support of host physiology and rhizosphere function, identifying the strain and its antibacterial proteins as complementary candidates for microbial- and protein-based management of tomato bacterial wilt.