Imidazolinone-resistant (IR) winter wheat allows selective control of jointed goatgrass with the herbicide imazamox. However, the spontaneous hybridization between jointed goatgrass and IR winter wheat threatens the value of the IR technology. The objectives of this study were to determine if F₁ hybrids collected in a commercial production field under IR winter wheat–fallow rotation in Oregon and their first-backcross progeny (BC₁) carried the Imi1 gene and were resistant to imazamox, and to analyze the parentage of F₁ and BC₁ plants. The average seed set of the F₁ spikes was 3.3%, and the average germination of BC₁ seed was 52%. All F₁ and BC₁ plants tested carried Imi1. Jointed goatgrass plant mortality was 100% when treated with imazamox at 0.053 kg ai ha⁻¹, compared to 0% for IR winter wheat and BC₁ progeny. All F₁ plants had jointed goatgrass as the maternal parent; whereas, most BC₁ plants (85.7%) were produced with IR winter wheat as the paternal backcross parent. Although the backcrossing of F₁ hybrids with jointed goatgrass is very low, it demonstrates the potential for introgression of Imi1 from IR winter wheat into jointed goatgrass under natural field conditions.

Nomenclature: Imazamox; jointed goatgrass, Aegilops cylindrica Host., AEGCY; winter wheat, Triticum aestivum L.