What lurks behind triple herbicide-tolerant oilseed rape?

• Author: Ho, Mae-Wan
• Position: Biodevastation

The surprising speed with which multiple herbicide-tolerant oilseed rape appeared in Canada and the United States raises serious questions over horizontal gene transfer and transgenic instability. Dr. Mae-Wan Ho reports. Triple herbicide-tolerant oilseed rape "volunteers" were first discovered in Alberta, Canada, in 1998. (1) A year later, these multiple herbicide-tolerant volunteers were found in a further 11 fields in Canada.

The United States only started growing herbicide-tolerant canola in 2001. Research in Idaho University showed that similar multiple genestacking had occurred over two years in experimental plots, and during the same period, weeds with two-herbicide-tolerant traits were found.

The speed with which triple-herbicide-tolerant oilseed rape has evolved gives cause for concern. I decided to review the original paper in detail.

A farmer in Alberta planted three varieties of GM oilseed rape (B. napus) in the same or adjacent fields in 1997. The varieties were tolerant to herbicides glyphosate, glufosinate, and imidazolinone respectively. In Field 1, the farmer started planting the glufosinate-tolerant variety, but, after 15 hectares, switched to the imidazolinone-tolerant for the remainder of the field. In Field 2 located across a road, 22 meters from the edge of the first field, he planted the glyphosate-tolerant variety.

In 1998, Field 1 was left fallow, and part of Field 2 was planted with the imidazolinone-tolerant variety. Weeds in the fallow Field 1 were sprayed with glyphosate, but the farmer noticed that B. napus volunteers in this field were not being controlled by the herbicide.

At this point, the Canadian government research team came and collected the B. napus volunteers that had survived the glyphosate treatments--9 from the part sown with glufosinate-tolerant variety and 25 from the part sown with imidazolinone--and grew them in the greenhouse to obtain seeds for further study.

The researchers considered two possibilities that might account for the presence of glyphosate-tolerant oilseed rape in Field 1. It could be transport of glyphosate-tolerant seeds from Field 2 across the road to Field 1 (most likely by farm equipment), or it could be cross-pollination between the glyphosate-tolerant variety and either the glufosinate- or imidazolinone-tolerant varieties. The glyphosate- and glufosinate-tolerant varieties were transgenic, and "homozygous for the trait coded by a single insert," that is two copies of a...