Coumarin application modulates antioxidant defense to enhance resistance against Fusarium in mung bean

Plant-derived bioactive compounds contribute a major role in plant defense against fungal pathogens. Among these, coumarin proved to be a major controller in root-pathogen interactions, exhibiting diverse protective mechanisms. This study investigates the effects of coumarin (50 mg.L^- 1), applied through seed priming and foliar spray, on the biochemical responses of Mung bean and its impact on root colonization by Fusarium solani. Mung bean seeds pre-treated with coumarin were sown under both infected and non-infected conditions. Once the seedling established up to two-leaf stage, weekly foliar sprays of 50 mg.L^- 1 coumarin (treatment group) and water (control group) were applied for 4 weeks. The results showed that the application of coumarin significantly reduced Fusarium colonization in Mung bean roots while enhancing shoot and root growth under pathogen stress. Coumarin treatment significantly increased leaf area, shoot density, and photosynthetic pigments. It also caused a substantial reduction in oxidative stress markers, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) contents. Antioxidant enzyme activities, including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (GPX) were markedly increased with coumarin treatment. Likewise, enzymes involved in secondary metabolism, such as polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), also showed increased activities. This was associated with higher levels of total phenolics and flavonoid alongside stronger antioxidant activitiy, indicated by DPPH and ABTS assays. HPLC analysis further revealed increased levels of gallic, coumaric, ferulic, and chlorogenic acids in coumarin-treated plants. These findings demonstrate that coumarin applications enhance the synthesis of beneficial secondary metabolites, strengthen plant defense mechanisms, and promote overall plant health. Therefore, coumarin shows a promising sustainable biostimulant for improving crop resilience and advancing eco-friendly agricultural practices.