Weeds and Outcrossing to Wild Species

The Concern

Concerns have been raised in recent years about what is called "outcrossing" - the potential for genes to move from a genetically engineered plant to a wild relative. The concern is that a trait that may be desirable in a crop plant, such as drought tolerance or tolerance to a specific herbicide, could be transferred to a wild relative via a plant's pollen. The theory is that the resulting offspring of these plants might then become increasingly difficult to control in the environment.

How concerns about outcrossing are being addressed

It is true that genes can be transferred from one plant of a species to another plant of the same species, and in some cases to a closely related but different plant species. This is called outcrossing, and it is a normal natural occurrence. Just as this can happen between non-genetically engineered plants, it can also happen between genetically engineered plants and non-genetically engineered plants.

Before plants with novel traits are authorized for release, they must undergo a full and comprehensive assessment to determine their environmental safety. One of the criteria evaluated during this assessment is the potential for gene flow to wild relatives. There are two components to that assessment: (1) the potential for gene flow, and (2) the potential impact of gene flow should it occur. If the potential for gene flow does exist then the assessment must focus on what the potential impact of such an outcrossing would be on the environment.

For the most part, genetically engineered plants that have been approved for release in Canada do not have wild relatives. This includes, for example, potatoes, tomatoes, corn, soybeans and flax.

Considerations with respect to outcrossing must be addressed on a case-by-case basis, taking into account the plant species, its biology and ecology in Canada, and the introduced novel trait. Guidelines are in place that require the potential for outcrossing to be evaluated in all environmental safety assessments.

Canola plants approved for commercial release are, however, known to outcross with other plants of the same species, and can cross with a few related plants of other species, e.g. Brassica rapa. In herbicide tolerant canola plants any tolerance genes transferred to wild relatives and that result in offspring, would only gain a competitive advantage in areas where the herbicide was being used to control weeds. In such areas, these plants can be controlled by other available mechanical or chemical means. Conclusions to date of such assessments have been that while gene flow is possible, it would not result in increased weediness or invasiveness of wild relatives.

This assessment process is in place to provide a comprehensive, science-based, evaluation of all plants with novel traits so that novel plants which do not meet the criteria for environmental safety are not released in Canada.

What's the big deal about weeds?

Anyone who has ever planted a garden knows that weeds can be annoying and harmful. Farmers face this battle on a large scale and have traditionally used a variety of methods to attempt to control weeds that threaten the productivity of their crops. Recently, scientists have used modern biotechnology to develop plants that are tolerant to commercial herbicides as a way for farmers to expand weed control options.

What is a "superweed"?

There have been claims that transfer of traits such as herbicide tolerance from plants produced through biotechnology to weeds could create "superweeds" that are harder to control or are more invasive. It should be noted that the phrase "superweed" is misleading. If a herbicide tolerant trait was passed onto a weed, it does not mean that the weed would become a bigger pest; it simply means that the weed would be tolerant to a specific herbicide. The weed could still be controlled using other management practices such as tillage or alternative herbicides.

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