Abstract
Multigenerational stress exposure induces stress memory in plants, influencing resource allocation, defence mechanisms, and productivity. Weed competition imposes both resource-based (abiotic) and allelopathic (biotic) stress, engaging overlapping hormonal pathways. This study examined the hormonal and transcriptomic mechanisms underlying multigenerational stress memory in wheat subjected to inter-specific competition with kochia and Italian ryegrass and intra-specific competition with other wheat plants. Phytohormone analysis revealed increased salicylic acid levels, promoting systemic acquired resistance, whereas jasmonic acid levels declined, indicating suppressed jasmonate-mediated defence. Abscisic acid responses varied, reflecting shifts in water-use efficiency. Cytokinins and auxins exhibited generation- and treatment-specific trends, suggesting adaptive resource acquisition but potential hormonal imbalances. These hormonal shifts corresponded with phenotypic responses, where adaptive benefits peaked at Generation 3 before transitioning to maladaptive responses in later generations. Transcriptomic analysis identified dynamic changes in differentially expressed genes (DEGs) and key pathways. Wheat-only competition peaked in stress-responsive DEGs in Generation 3, while wheat-kochia and wheat-ryegrass exhibited early generation transcriptional reprogramming and long-term adaptations. Intra-specific wheat competition showed early generation transcriptomic surges but persistent growth repression in the current study. These findings provide mechanistic insights into multigenerational stress memory mechanisms and reveal how phytohormonal crosstalk and transcriptional reprogramming shape wheat responses to competition stress across generations.