Abstract Key message The early flowering system HSP:: AtFT allowed a fast evaluation of a gene containment system based on the construct PsEND1:: barnase–barstar for poplar . Transgenic lines showed disturbed pollen development and sterility. Abstract Vertical gene transfer through pollen flow from transgenic or non-native plant species into their crossable natural relatives is a major concern. Gene containment approaches have been proposed to reduce or even avoid gene flow among tree species. However, evaluation …