Feb 10, 2003

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New focus for scientific debate

Outcrossing: What of it?

Hybridisation between related plants is a biological principle. When genetically modified plants are involved, however, it tends to arouse suspicion amongst the general public. Ecological safety research has long focused in particular on whether and in what circumstances outcrossings are possible. The perspective has now changed: What would be the consequences of genetically modified plants passing on a new trait? Not every outcrossing constitutes ecological damage.

Outcrossing takes place, but what does this mean? This issue has been the subject of debate at several scientific conferences in recent months. There, and in scientific articles, a series of case studies with very varied findings has been presented.

At a European Science Foundation workshop in Amsterdam in late January 2003, some contributors looked at genetically modified oilseed rape as a source for the spread of transgenes.

Up for discussion again was a GM sunflower trial conducted by US ecologist Allison Snow’s team at Ohio State University. She had previously submitted her findings for discussion at the International Biosafety Symposium in Beijing (October 2002).

Sunflowers: Bt toxin has an ecological advantage

In some parts of the USA, feral sunflowers are regarded as an unwelcome weed by farmers, because they compete with field crops for light and nutrients. There are no barriers to hybridisation in the fields between the wild sunflowers and the cultivated forms. Against this background, Snow’s findings give cause for concern. She had conducted trials with genetically modified sunflowers that produce the Bt toxin to protect them from moth larvae. Contrary to expectations, the Bt sunflowers had an advantage over their conventional relatives: They are better able to persist in their natural environment outside the field. With sunflowers the weed problem would therefore be aggravated by the introduction of the Bt gene.The Bt toxin produced in the transgenic sunflowers is harmful to its chewing pest. Consequently the sunflowers develop better than conventional plants and produce more seeds, which in turn results in more seedlings. The Bt toxin gene spreads through the population. At the workshop in Amsterdam Diana Pilson, a member of Allison Snow’s team, suggested that data for Bt sunflowers indicates an increase in the number of plants and a greater quantity of seed in the soil.

This hypothesis will now be tested in further trials.

Allison Snow and her team had engineered Bt sunflowers which produced no pollen. This enabled them to conduct the trial in field conditions without running the risk of spreading the transgenic trait. Bt sunflowers are not authorised for commercial cultivation in the USA.

Oilseed rape: Transgenic weedy turnips are less fit

A group headed by Neal Stewart from the University of Tennessee (Knoxville), which also presented its findings in Amsterdam, came to different conclusions. They had transferred the Bt toxin gene to oilseed rape plants and then crossed these with turnip mustard (Brassica rapa), a close relative of oilseed rape and a common weed. The rape-turnip mustard hybrids obtained in this way were crossed again with turnip mustard. The aim was to investigate the widespread fear that this is how “super weeds” develop. Stewart planted these second-generation turnip mustard plants derived from transgenic Bt rape in wheat fields, where they proved to be 20% less persistent than conventional turnip mustard. This trial therefore failed to confirm the super weed theory.

Ecological damage?

Outcrossings from transgenic plants to related wild species do not always automatically constitute ecological damage. The consequences of outcrossing vary depending on the plant, the trait and the ecosystem. Furthermore, Allison Snow acknowledged that the “population dynamic consequences” of her findings were difficult to assess without long-term research.

There is another reason why it is not easy to assess the consequences of potential outcrossings of transgenes: Neither society as a whole nor the scientific community has a generally accepted perception of what is meant by the term “ecological damage”. Ecosystems are dynamic and in constant flux. Changes in species composition are not unusual. If a transgenic plant were to have a specific effect within this process, what would determine whether it was good or bad?

Even the two studies on Bt sunflowers and Bt oilseed rape preferred to examine the possible consequences using concrete, tangible criteria: Whether there are more or fewer persistent weeds is predominantly an economic problem rather than an ecological one.