Escaped GMO canola plants persist long-term, but may be losing their engineered resistance to pesticides

Populations of canola plants genetically engineered to be resistant to herbicides can survive outside of farms, but may be gradually losing their engineered genes, reports a new study led by Cynthia Sagers of Arizona State University, US, published May 22 in the open-access journal PLOS ONE.

The hypothesis has been put forward that if any genetically engineered crop plants escape farm fields, they will be short-lived. This would make them unlikely to take over wild areas or spread their inserted genes, called transgenes, to wild populations of closely related plants. However, there have been few studies to see if populations of these "feral" crop plants can in fact survive in the wild long term.

In the new study, researchers conducted a large-scale survey of populations of genetically engineered canola living along roadsides in North Dakota, repeating a survey they initially conducted in 2010.

They found that the total number of feral canola plants in the sample had decreased and populations of the plants became less common over time. When they tested the plants for herbicide resistance, they saw that the types of herbicides the plants were resistant to had shifted over time, likely due to changes in the varieties farmers were planting.

Importantly, almost one quarter of the feral plants were not resistant and did not contain transgenes—up from 19.9% in 2010 to 24.2% in 2021—suggesting that these populations may be losing their transgenes.

The researchers hypothesize that feral canola populations may be under evolutionary pressure to shed the transgenes, which could happen if the engineered canola are at a disadvantage once they are no longer being cultivated on a farm.

Further genetic analysis could help clarify the plants' origins and yield more information on how long transgenes can persist in the environment.

Steven Travers says, "The assumption that transgenic crop varieties will be restricted to the benign conditions of ag fields and not inter-mix with natural plant populations can be rejected. Self-sustaining, long-term feral populations of canola (some transgenic and some not) are a world-wide phenomenon and as such emphasize the need for more research on how de-domestication works, the extent to which it impacts natural populations, and the risks that the adventitious presence of transgenes might represent to agriculture."