Jul 9, 2007
“Coexistence requires greater effort, but is possible in principle.”
Dr Antje Dietz-Pfeilstetter , Institute for Plant Virology, Microbiology and Biosafety. Federal Biological Research Centre for Agriculture and Forestry (BBA) Braunschweig (later JKI /Julius Kühn Institute). Coordinator of the SiFo joint project on potential impacts of the cultivation of transgenic oilseed rape, 2001-2004
Is GM oilseed rape capable of coexisting with conventional rape? – Questions put to Antje Dietz-Pfeilstetter.
GMO Safety : In the past few years you have dealt intensively with the outcrossing behaviour of oilseed rape. You have conducted on-farm trials lasting several years and have recently presented a comprehensive literature study. So how prone to outcrossing is oilseed rape?
Antje Dietz-Pfeilstetter: Oilseed rape is self-fertilising and its propensity to outcross is relatively low compared with maize. Even with direct plant contact, cross-fertilisation takes place only 25 to 30 per cent of the time. In field trials where we planted GM and non-GM rape next to each other, we found only one to ten per cent GM oilseed rape in the contact zone in the non-GM rape field. The outcrossing rate drops sharply just five to ten metres from the GM rape field.
GMO Safety: How relevant is long-distance transport? Pollen from GM rape can be carried over long distances to conventional fields by the wind or by bees.
Antje Dietz-Pfeilstetter: The higher the proportion of GM oilseed rape fields in a growing region, the higher the potential GMO presence. However, here we are dealing with isolated events that are usually caused by insects. Wind plays hardly any role in the long-distance transport of pollen. Insects can carry pollen three to four kilometres and further in some cases. The level of contamination is generally to be regarded as very small.
GMO Safety: What measures are useful for minimising incrossings from neighbouring GM rape to conventional rape fields? Do you recommend buffer plantings?
Antje Dietz-Pfeilstetter: Our working group and others have conducted experimental research on this topic. With oilseed rape fields of the same size, at distances greater than ten metres we found incrossings of only 0.1 to 0.3 per cent on the non-GM field when the fields were ten metres apart. Buffer planting of five to ten metres is therefore the most effective measure. And works best when planted along the non-GM rape field on the side facing the GM rape field. Additional/alternative measures are adequate separation distances. Another possibility would be buffer plantings around the GM rape field.
GMO Safety: Oilseed rape can also survive as volunteer rape off the field, e.g. along field margins and railway lines. How relevant are such populations for coexistence?
Antje Dietz-Pfeilstetter: They are of very little, if any, relevance. This was clearly shown in our research and in an EU joint research project. We are dealing here with rape populations that have temporarily gone wild, that do not occur all the time, and often disappear again the following year. Oilseed rape is not very competitive off the field.
GMO Safety: Oilseed rape seeds can survive for a long time in the soil and can keep germinating again during the crop rotation. If GM rape and conventional rape are grown on one farm, such volunteer plants would be a source of GMO presence in conventional crops.
Antje Dietz-Pfeilstetter: Volunteer rape is the factor with the greatest significance. If it is not properly controlled on a farm, coexistence cannot be guaranteed in the long term. Soil cultivation after the rape harvest, systematic control of volunteer rape plants and suitable crop rotation are the most important levers for keeping volunteer rape under control.
GMO Safety: Is current farming practice adequate for controlling volunteer rape from a coexistence point of view?
Antje Dietz-Pfeilstetter: Safeguarding the coexistence of GM and non-GM rape in the long term requires greater effort. In order to minimise the seed potential of GM rape in the soil, as many seeds as possible should be made to germinate immediately after harvesting. This is most effective when ploughing does not take place until a few weeks later. And I can only repeat: systematic control of volunteer rape in follower crops, such as cereals, is important.
GMO Safety: Oilseed rape has wild relatives in Europe with which it could outcross. How relevant are such incrossings to wild relatives for the dispersal of oilseed rape in arable crops?
Antje Dietz-Pfeilstetter: Oilseed rape may have lots of relatives, but in Europe the only outcrossings that are really relevant are those with turnip rape. Relevant means that the outcrossing results in progeny that are fertile and can in turn produce fertile progeny. Turnip rape is not found much in most regions of Germany. It is more common in Denmark and is probably a crop plant that went wild.
GMO Safety: The ‘super weed’ scenario keeps recurring in public debate. What does it refer to?
Antje Dietz-Pfeilstetter: This is a very fuzzy term. In the context of herbicide-tolerantGM oilseed rape a number of different scenarios are conceivable. Firstly, if the same herbicide is used repeatedly, resistant weeds may develop. There are numerous examples of this, but this kind of scenario is not specifically linked to genetic engineering – it depends on the herbicide used. If something like this occurs, the farmer has to change herbicides. Secondly, herbicide-tolerant GM rape outcrosses with related arable weeds, transferring the gene for herbicide tolerance to the weeds. This results in the formation of herbicide-tolerant weeds. However, as already explained, this has been of little, if any, relevance until now because of a lack of outcrossing partners. And thirdly: the herbicide-tolerant GM volunteer rape emerges as weeds in the subsequent crops, usually cereal. In this case, it can be controlled using standard conventional cereal herbicides. In summary, one can say that what is important is to have farsighted crop management.
GMO Safety: Now to the summing-up and your conclusions. Can GM and conventional oilseed rape crops be grown alongside one another in the long term with a justifiable level of effort?
Antje Dietz-Pfeilstetter: Whether the level of effort required is justifiable depends on the benefits to the farmer. The cultivation of GM and non-GM oilseed rape in a region certainly requires greater caution on the part of the farmers and well thought-out crop management, including the mutual exchange of information.
GMO Safety: Thank you for talking to us.
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GM rape seed: Canada and Australia
- Julius Kühn-Institut (JKI)), Institut für Sicherheit in der Gentechnik bei Pflanzen
- Hüsgen A., Dietz-Pfeilstetter A. (2008) Parameters Affecting Gene Flow in Oilseed Rape, ISB News Report
- Hüsken A., Dietz-Pfeilstetter A. (2007) Pollen-mediated intraspecific gene flow from herbicide resistant oilseed rape (Brassica napus L.), Transgenic Research