Comparative biochemical responses of sorghum (Sorghum Bicolor L. Moench) and rice (Oryza Sativa L.) to simulated caterpillar herbivory: alterations in soluble sugars and phenolic metabolism associated with induced defense

Herbivore-associated stimulation can alter primary and specialized metabolism, but comparative biochemical responses of cereal crops remain insufficiently characterized. This study investigated changes in soluble sugars and targeted phenolic acids in sorghum (Sorghum bicolor L. Moench) cultivar Epuripur sorghum and NERICA 9 rice following simulated caterpillar herbivory. Plants were subjected to mechanical leaf wounding followed by application of diluted oral secretions from fourth- and fifth-instar Mythimna loreyi larvae (WOS), while untreated plants served as controls. After 24 h, leaf tissues were analyzed by high-performance liquid chromatography (HPLC) for glucose, fructose, and seven targeted phenolic acids. Two-way ANOVA evaluated effects of plant material, treatment, and their interaction. WOS treatment significantly reduced glucose and fructose concentrations in both materials (P < 0.001), with significant plant material × treatment interactions. Several phenolic acids increased or became detectable following WOS treatment, including p-hydroxybenzoic, vanillic, syringic, p-coumaric, cinnamic, and chlorobenzoic acids. Significant plant material × treatment interactions occurred for most phenolic acids, whereas the interaction for p-coumaric acid was not significant (P = 0.205). Epuripur sorghum generally exhibited higher concentrations of several metabolites than NERICA 9. These findings indicate material-specific biochemical responses to simulated caterpillar-associated stimulation involving changes in both primary and phenolic metabolism. However, the study does not establish carbon allocation, growth–defense trade-offs, or direct insect resistance. Because wounding-only and oral-secretion-only treatments were not included, their individual effects could not be separated. The results provide candidate biochemical responses for further investigation using direct herbivore feeding, multiple genotypes, time-course sampling, and physiological and insect-performance measurements.