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Transgenes that have escaped from glyphosate-resistant canola can persist in the wild.

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

Inserted Transgenes and Intended Effect: CP4 EPSPS gene derived from the common soil bacterium Agrobacterium sp. (Strain CP4) to convey resistance to the herbicide glyphosate. The gene was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the gene would be expressed in all parts of the plant.

Goal of This Study: Investigate whether naturally occurring cross-pollination between transgenic glyphosate-resistant canola and wild field mustard (Brassica rapa), which is a common weed and grows in and around agricultural fields, leads to stable incorporation of the transgene into field mustard populations.

Results of This Study: In 2001, hybrids between glyphosate-resistant canola and field mustard were found in field mustard populations growing in field margins on two farms in Quebec, Canada. Glyphosate-resistant canola had been planted on the adjacent fields, but after 2001 was no longer planted and no spraying of glyphosate occurred after 2002. One site was monitored for hybrids in 2003 and 2005. In 2003, 85 of 200 plants surveyed were glyphosate-resistant hybrids. In 2005, five out of 200 plants surveyed were glyphosate-resistant hybrids. The transgenic hybrids had reduced pollen fertility, but nonetheless produced fertile offspring. So despite reduced fertility and the lack of selective advantage (since no glyphosate had been sprayed since 2002), the transgene was incorporated into a weedy field mustard population.

Since at both sites transgenic canola volunteers were detected during the study period, ongoing new hybridization could occur, increasing the likelihood of long-term persistence of the transgene in field mustard populations.

Additional Comments: The authors remark, "these experiments show the importance of conducting risk assessment studies on transgenic hybrids under realistic agricultural/field conditions" (p. 7). Persistence of herbicide-resistant weedy field mustard in agricultural settings where glyphosate is applied could increase weed problems for farmers. And although the authors see little inherent risk of herbicide-resistant weedy field mustard outside of such settings, they point out that with other genetically engineered traits (such as insect or disease resistance), the risks associated with transgenes escaping to wild relatives may be significantly greater.

Source: Warwick, S. I., A. Legere, M.-J. Simard, and T. James (2007). "Do Escaped Transgenes Persist in Nature? The Case of an Herbicide Resistance Transgene in Weedy Brassica rapa Population," Molecular Ecology doi: 10.1111/j.1365-294x.2007.03567.x

Author Affiliations: Agricultural and Agri-Food Canada (Canadian government ministry).

Funding: Not reported.

Product Status: Transgenic glyphosate-resistant canola is grown commercially in Canada and the USA. The main brand is Monsanto's Roundup Ready® canola.

Copyright 2008 The Nature Institute.

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