Comparison of the performance of bromoxynil-resistant and susceptible near-isogenic populations of oilseed rape

Bromoxynil herbicide resistance is the newest type of broad-spectrum, non-selective herbicide resistance to be introduced into oilseed rape (Brassica napus L.). This herbicide resistance is conferred by a single transgene (the oxy gene), taken from a soil bacterium, which confers the ability to metabolize hydroxybenzonitrile herbicides such as bromoxynil. The level of resistance to bromoxynil herbicide in oilseed rape is high, but it is not known whether there are any performance changes associated with the oxy transgene or with the derived herbicide resistance. To determine if there are changes in performance related to the oxy transgene, or the derived herbicide resistance, two near-isogenic transgenic bromoxynil-resistant populations, with two different forms of the oxy gene, Westar 235 and Westar 237, were developed at the University of Manitoba, grown in the field in Manitoba for several years and evaluated for comparative performance. Westar 235 and Westar 237 near-isogenic populations, either sprayed with bromoxynil at 280 g a.i. ha–1 or left unsprayed, were compared with the non-transgenic near-isogenic population cultivar, Westar, in Winnipeg, Carman, and Portage la Prairie from 1994 to 1997. There were no consistent differences in the performance of the sprayed or unsprayed transgenic near-isogenic populations in comparison to Westar for any trait. The few significant and minimal differences that were found were evenly divided between positive effects and negative effects of the oxy gene and derived herbicide resistance. There were no significant effects of spraying bromoxynil herbicide detected in paired comparisons of Westar 235 and Westar 237 sprayed versus Westar 235 and Westar 237 unsprayed, respectively. The effects of the oxy transgenes and the effects of bromoxynil spraying of herbicide-resistant lines were negligible, indicating that there is little, if any biological cost associated with the bromoxynil resistance transgenes or related herbicide resistance. Key words: Transgenic oilseed rape, Brassica napus, biological cost