Omics Integration Reveals Hormonal Adjustments in Irrigated and Nonirrigated Rice Varieties Upon Mythimna separata Feeding.

Freshwater consumption is the biggest challenge in irrigated rice cultivation (Oryza sativa L.). Nonirrigated farmland rice cultivation is a strategy to mitigate the water resource shortage associated with traditional irrigated rice farming. Both nonirrigated farmland and irrigated rice face challenges from insect pest attacks, yet the comparative responses of rice grown under these two cultivation methods to insect herbivory have not been extensively studied. In this study, we observed that the population density of the oriental armyworm (Mythimna separata) was higher in nonirrigated farmland rice compared to irrigated rice. To investigate the molecular and metabolic responses of rice to insect feeding, we conducted integrated transcriptomic and metabolomic analyses following 48 h of continuous herbivory by oriental armyworm larvae. Our results showed that insect feeding induced a more pronounced change in the number of differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in irrigated rice than in nonirrigated farmland rice. These DEGs and DAMs were significantly enriched in plant hormone signal transduction pathways. In-depth analysis revealed that the abscisic acid and salicylic acid signaling pathways and the auxin biosynthesis pathway were more responsive to oriental armyworm feeding in irrigated rice compared to nonirrigated farmland rice. Additionally, jasmonic acid biosynthesis and signaling pathways were activated in both irrigated and nonirrigated farmland rice under herbivory stress. In summary, this study provides evidence that nonirrigated farmland rice exhibits a reduced response to insect feeding compared to irrigated rice. These findings contribute to nonirrigated farmland rice resistance or tolerance research and potential applications in pest management.