Biochemical Defenses of Tomato in Response to Multiple Herbivory Damage Under Contrasting Irrigation Environments

Water limitation and herbivore attack frequently co-occur in agricultural systems, yet defense-related biochemical responses under these combined conditions remain difficult to predict, particularly during simultaneous attack by multiple herbivore species. We investigated how defense responses in field-grown tomato (Solanum lycopersicum L.) differed between irrigation environments and according to herbivore species identity and combination. Well-watered and water-deficit plants were exposed to the spider mites Tetranychus evansi and Tetranychus urticae and the tomato leafminer Tuta absoluta, individually or in interspecific combinations involving two or three species. Plants received either 100% or 50% of the estimated crop water requirements, with leaves collected before and after seven days of herbivore feeding. Gravimetric soil moisture was 21.1% in the water-deficit sector and 29.0% in the well-watered sector. Hormonal responses differed between irrigation environments and among herbivore treatments, with significant interactions for abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), indole-3-acetic acid (IAA), and zeatin. ABA and SA concentrations were generally higher in the water-deficit environment, whereas JA concentrations were generally higher in the well-watered environment. IAA and zeatin exhibited distinct responses associated with T. urticae infestation under water-deficit conditions. Proline concentrations were generally higher in the water-deficit environment. Simultaneous infestations involving two or three herbivore species were associated with distinct biochemical response patterns, particularly in lipoxygenase (LOX), polyphenol oxidase (PPO), and trypsin inhibitory activity (TIA). Fruit production also differed between irrigation environments, whereas the proportion of fruits damaged by Neoleucinodes elegantalis was similar (29.3% and 30.8% in well-watered and water-deficit environments, respectively). Overall, these findings indicate that tomato hormonal and biochemical responses to herbivory vary with irrigation environment and herbivore community composition, highlighting the context-dependent nature of plant responses to combined abiotic and biotic challenges.