Metabolomic Analysis of Tomato Plants Treated With Garlic Extract, Bacillus subtilis, and Their Combination for Defense Against Bacterial Wilt

Ralstonia solanacearum, the causal agent of bacterial wilt, severely disrupts the vascular function of tomato plants, leading to significant yield losses. This study aimed to investigate the metabolomic shifts in tomato plants treated with garlic (Allium sativum) crude extract, Bacillus subtilis, and their combination, to assess their roles in enhancing resistance to R. solanacearum. Metabolomic profiling was conducted using ultra-high performance liquid chromatography coupled with quadruple time-of-flight mass spectrometry (UHPLC-qTOF-MS) to identify and quantify key metabolites associated with stress response. Multivariate statistical analysis (MVDA) tools, viz. principal component analysis (PCA) and the orthogonal projection to latent structures-discriminant analysis (OPLS-DA) loading scatter plot were used to identify the metabolites that are positively and negatively correlated to bacterial wilt infection. The profiling revealed that garlic extract up-regulated key phenolic compounds, including chlorogenic acid and caffeoyl glucaric acid, which contribute to pathogen defense by reinforcing cell structures and mitigating oxidative stress. Chlorogenic acid accumulation was notably prominent in garlic-treated plants, while caffeoyl glucaric acid exhibited variable regulation across the treatments. Flavonoid levels were generally down-regulated, indicating a metabolic shift favoring phenylpropanoid pathways in response to disease stress. Additionally, lipid-related metabolites, such as 12-dienoate, were reduced in the combined treatment, whereas Juniperoside III was up-regulated in B. subtilis-treated plants, suggesting selective regulation of saponin metabolism. These findings indicate that garlic extract enhances plant defense primarily through phenylpropanoid-mediated structural reinforcement, while B. subtilis contributes to disease suppression through microbial interactions rather than significant metabolic shifts. Understanding these metabolic trade-offs offers valuable insights into optimizing bacterial wilt management strategies, ultimately improving tomato resilience and productivity.