Role of Jasmonic Acid in Phytochemical Modulation and Nematode Resistance in Early-Stage Tomato Seedlings under In Vitro Conditions

Abstract Across the globe, tomato crops are severely affected by root-knot nematodes, particularly Meloidogyne incognita, which significantly reduce yield and quality of this economically important crop. Conventional management strategies relying on chemical nematicides and fertilizers are often associated with environmental concerns; therefore, alternative plant-based defense regulatory approaches are required. This study evaluates the role of signaling phytohormone jasmonic acid (JA), involved in plant defense signaling, in modulating the response of Solanum lycopersicum under nematode stress and enhancing phytochemical accumulation. Tomato seedlings were primed with JA at two concentrations (0.25 and 0.5 mM) and maintained under in vitro conditions with a completely randomized experimental design (three biological replicates per treatment). Following germination, seedlings were inoculated with second-stage juveniles (J2) of M. incognita under controlled conditions. The experiment was conducted for seven days post-inoculation, and growth parameters, photosynthetic pigments, secondary metabolites, antioxidant enzymes, and protein content were analyzed. Results indicated a significant reduction in growth parameters due to nematode infection, whereas JA-treated seedlings exhibited improved root and shoot growth (root: 31.13%, shoot: 20.59%), biomass accumulation (root: 42.11%, shoot: 57.19%), chlorophyll content (chlorophyll a: 24.24% increase; chlorophyll b: 51.52% increase), enhanced secondary metabolites (phenol: 44.62%, flavonoids: 25.46%), elevated protein content (54.53%), and increased polyphenol oxidase activity (50%) compared to infected controls. Overall, exogenous JA application was associated with enhanced plant tolerance and reduced nematode-induced damage, as evidenced by a 49.37% reduction in gall formation. Collectively, the findings suggest that jasmonic acid-mediated regulation of phytochemical and defense responses represents a promising approach for improving early-stage seedling resilience under nematode stress in vitro.