Introgression of an imidazolinone-resistance gene from winter wheat (Triticum aestivum L.) into jointed goatgrass (Aegilops cylindrica Host)

Imidazolinone-resistant winter wheat (Triticum aestivum L.) is being commercialized in the USA. This technology allows wheat growers to selectively control jointed goatgrass (Aegilops cylindrica Host), a weed that is especially problematic because of its close genetic relationship with wheat. However, the potential movement of the imidazolinone-resistance gene from winter wheat to jointed goatgrass is a concern. Winter wheat and jointed goatgrass have the D genome in common and can hybridize and backcross under natural field conditions. Since the imidazolinone-resistance gene (Imi1) is located on the D genome, it is possible for resistance to be transferred to jointed goatgrass via hybridization and backcrossing. To study the potential for gene movement, BC₂S₂ plants were produced artificially using imidazolinone-resistant winter wheat (cv. FS-4) as the female parent and a native jointed goatgrass collection as the male recurrent parent. FS-4, the jointed goatgrass collection, and 18 randomly selected BC₂S₂ populations were treated with imazamox. The percentage of survival was 100% for the FS-4, 0% for the jointed goatgrass collection and 6 BC₂S₂ populations, 40% or less for 2 BC₂S₂ populations, and 50% or greater for the remaining 10 BC₂S₂ populations. Chromosome counts in BC₂S₃ plants showed a restoration of the chromosome number of jointed goatgrass, with four out of four plants examined having 28 chromosomes. Sequencing of AHASL1D in BC₂S₃ plants derived from BC₂S₂-6 revealed the sexual transmission of Imi1 from FS-4 to jointed goatgrass. Imi1 conferred resistance to the imidazolinone herbicide imazamox, as shown by the in vitro assay for acetohydroxyacid synthase (AHAS) activity.