Superweeds: are GM trials a danger to society?
George Weller examines some of the perceived dangers of GM trials and why, he believes, they do not pose a serious threat after all.
by George Weller
Thursday 28th June 2012, 19:58 BST
Genetic modification (GM) was once again in the news this year as protesters attempted to halt a GM wheat trial at Rothamsted Research. GM technology can provide crop plants with enormous advantages. However, as protesters argued at Rothamsted if these advantages are accidentally transferred to wild plants the consequences could be serious. Fortunately as many commenters pointed out at the time, this is extremely unlikely to happen due to the way that wheat is pollinated.
The reason this is so unlikely is because modern agricultural wheat usually self-pollinates. The pollen grains produced in a flower fertilise eggs inside that same flower, often before the flower has even opened. The small amount of pollen that does eventually leave the flower is carried by the wind and its dispersal is limited by its relatively high weight. In a recent experiment, GM wheat was planted two and a half metres away from non-GM wheat and only 0.03% of the seeds produced by the non-GM plants were the result of cross-pollination from the GM plants. Besides, even if some GM pollen did escape and land on a wild relative of wheat, successful pollination is unlikely to occur, since agricultural wheat has a very different genetic structure to even its closest wild relatives.
Unfortunately, extremely unlikely is not the same as impossible. It would only take a single grain of GM pollen to get caught by a strong wind and, by pure fluke, travel far enough to reach wild relatives and it just might, against the odds, fertilise a non-GM plant, resulting in uncontrolled spread of the new gene.
This potential ‘GM contamination’ could have damaging consequences. Whatever favourable trait had been introduced to the original GM plant (for example, the ability to repel hungry insects or survive herbicide treatment) would now be found in the ‘contaminated’ wild plant. If this new ability conferred a great enough advantage, then the wild plant could become a ‘superweed’. It would grow and reproduce so successfully that it might prevent the growth of other plants, resulting in a loss of biodiversity. Such weeds could also cause problems for agriculture if they spread into farmers’ fields. Fortunately, new approaches in genetic engineering should soon make these events impossible.
One of these new approaches is to engineer the GM plants to be sterile. The plants are manipulated in such a way that any seeds they produce are unable to germinate and produce new plants. This means that even if GM pollen does manage to escape its field and find a wild plant that it is able to fertilise, the offspring produced will be destined to remain as seeds and will never grow up into potentially harmful weeds. There is, however, a major problem with this strategy. It prevents farmers from being able to save their seed and replant it the following year. It has been heavily criticised by the anti-GM lobby, who dubbed it ‘terminator technology’, because it could cause farmers to become dependent on seed companies to sell them new seeds each year.
An alternative strategy that avoids this problem is to engineer the plants in such a way that the GM trait can only be inherited from the mother. The pollen (which is male) is able to leave the plant on which it is produced, whereas the egg cells (female) stay put and wait for incoming pollen to fertilise them, leading to the formation of a seed. It is possible to create a GM plant in such a way that the new gene is found only in the eggs and not the pollen. This means that there is no chance of the new gene escaping the field, but the eggs can still be fertilised to produce GM seeds that can be planted the following year. This has already been achieved for several crops plants by inserting the desired new gene into special locations within the cell.
In conclusion we should continue testing GM crops, but it is vitally important that we also use technologies that lower the risk of cross-pollination. Even though cross-pollination is already very unlikely, it is still important to use these technologies because very unlikely is not the same as impossible, and in theory the consequences of cross-pollination could be very serious.