Herbicide-resistant weeds exploit their kinship to reduce allelopathy from wheat and rice

Kin recognition enables plants to optimize growth strategies when competing with heterospecific neighbors; however, its prevalence in herbicide-resistant weeds and how such weeds exploit kinship to interact with allelopathic crops remain largely unknown. In this study, we found that kin recognition occurred in 4 out of 10 tested herbicide-resistant weed biotypes from wheat and rice paddy fields. Root segregation treatments confirmed that kin recognition was mediated by root-secreted chemical signals. When interacting with allelopathic rice and wheat, weed biotypes possessing kin recognition exhibited striking plasticity. Kinship-based pairing reduced root allocation but accelerated flowering and increased seed production. Crucially, herbicide-resistant weed biotypes growing with kin had lower concentrations of the general stress-signaling carotenoid compound (-)-loliolide in the roots, and this was associated with reduced production of allelochemicals in the crops and reduced crop-mediated growth inhibition. This cascade allowed the weeds to reallocate resources toward reproduction and to reduce defense investment in crops, thus revealing a novel 'signal-mediated mutual de-escalation' strategy. Our findings suggest that kin recognition is an adaptive trait in herbicide-resistant weeds, reducing allelopathy from crops through (-)-loliolide-mediated chemical interactions. By modulating crop signaling systems, herbicide-resistant weeds exploit kinship for population expansion in agroecosystems, an adaptation strategy that should be considered when developing integrated weed management approaches.