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Experimental cross-pollination between transgenic herbicide-resistant canola and wild field mustard led to highly fertile, herbicide-resistant wild field mustard.

Manipulated Organism: Canola (Brassica napus ssp. Oleifera), otherwise known as oilseed rape.

Inserted Transgenes and Intended Effect: Bar gene from the bacterium Streptomyces to make canola resistant to the bleaching herbicide glufosinate. Glufosinate is the active ingredient in the herbicides Basta, Buster, Radicale, etc. In this study the researchers used a transgenic line of Drakkar oilseed rape, serial number 93B1104, developed by Plant Genetic Systems, Belgium.

Goal of This Study: Investigate the likelihood that naturally occurring cross-pollination between transgenic canola and field mustard (Brassica rapa) might create viable field mustard populations that are also resistant to the herbicide. The researchers cross-pollinated transgenic glufosinate-resistant canola with its weedy relative, field mustard.

Results of This Study: Glufosinate-resistant field mustard plants arose through crossing with glufosinate-resistant canola. The field mustard plants were as fertile and produced as many seeds as unmanipulated field mustard grown in the same growth rooms: "There were no significant differences between transgenic and nontransgenic plants in survival or the number of seeds per plant" (p. 605). In other words, the fact that the field mustard plants had incorporated and expressed the gene construct for glufosinate-resistance did not reduce their survival fitness.

Additional Comments: Cross-pollination between canola and field mustard is not an infrequent occurrence. When field mustard grew within a canola field, and, in addition both weed and crop flowered at the same time, up to 69% of the field mustard seeds were found to be hybrid seeds. The researchers of the study conclude: "Our results support the widespread assumption that once a transgenic trait such as glufosinate resistance has been selected for marketing, it is not likely to entail a strong fitness disadvantage when transferred to weedy B. rapa populations. . . . Also, there is some practical urgency for knowing more about this particular weed-crop complex because B.rapa is already a serious weed of more than 20 crops in over 50 countries . . . and glufosinate-resistant oilseed rape is now being grown commercially. If further field experiments also demonstrate little or no costs associated with transgenic resistance to glufosinate, it is possible that the spread of this transgene to natural populations of B. rapa will lead to infestations that are more difficult to control" (p. 613).

Source: Snow, A. A., B. Andersen, and R. Bagger Jørgensen (1999). "Costs of Transgenic Herbicide Resistance Introgressed from Brassica napus into Weedy B. rapa," Molecular Ecology vol. 8, pp. 605-15.

Author Affiliations: Risø National Laboratory, Denmark; Ohio State University.

Funding: Danish Nature and Forestry Agency; Novo Nordisk Foundation; Department of Plant Biology and Biogeochemistry, Risø National Laboratory; Danish National Bank.

Product Status: Transgenic glufosinate-resistant canola varieties are grown commercially in Canada and the U.S.A.

Copyright 2008 The Nature Institute.

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