Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/1998
Publication Date: N/A
Citation: Interpretive Summary: Jointed goatgrass, which is genetically related to wheat, is a serious weed problem in the winter wheat growing areas of the western United States. The herbicide imazamox has been developed by American Cyanamid and it will kill wheat, jointed goatgrass, and other weeds. American Cyanamid also developed a wheat that is resistant to imazamox. One of the concerns of using herbicide-resistant crops is the possibility of the herbicide-resistant crop cross pollinating with a closely related weed which would result in the transfer of the resistance gene to the weed. During the second year of conducting research with imazamox-resistant winter wheat at Pullman, Washington, two hybrid plants were found that were resistant to the herbicide. These hybrid plants were the result of a cross between the imazamox-resistant wheat and jointed goatgrass. In greenhouse trials, six of the seven seeds produced by these two hybrids were found to be resistant to the herbicide. The rapid transfer of the resistance gene from crop to weed has important implications for the use of herbicide-resistant winter wheat for the control of jointed goatgrass. Because of the biology of jointed goatgrass/winter wheat hybrids, it was possible to develop a management strategy that will reduce the occurrence of these resistant hybrids. This management strategy will also be effective in reducing the rate of the development of herbicide resistance in other weeds found in winter wheat.
Technical Abstract: Imazamox-resistant hybrids resulted from a cross between jointed goatgrass and an imazamox-resistant wheat ('cv' FS-4 IR wheat) with the wheat being the maternal parent. Two imazamox-resistant hybrids were discovered in a research plot where FS-4 IR wheat seed had been replanted from the harvest of an efficacy study conducted the year before. These hybrid plants survived imazamox applied at 0.053 and 0.069 kg ai/ha in the field and contained seven viable seeds (F2). These seeds were germinated and chromosomes were counted from the roots (2n number ranged from 39 to 54). In the greenhouse, six of the seven plants survived an application of 72 kg ai/ha imazamox which confirmed that the resistance trait had been passed from wheat to jointed goatgrass. The plants were vernalized for eight weeks. A large amount of phenotypic variation was observed in the mature F2 plants. A genetic description of the movement of the resistant- gene is given based on the case of the gene being located on the D and the A or B genomes. Management strategies to reduce the occurrence of herbicide-resistant hybrids are discussed.