Pollen dispersal between fields of GM and non-GM oilseed rape: Meta-analysis of available data and the possibilities for co-existence.

Christian Damgaard & Gösta Kjellsson, The National Environmental Research Institute (NERI), Department of Terrestrial Ecology, Vejlsøvej 25, DK-8600 Silkeborg, Denmark.

e-mail: cfd@.dmu.dk, gk@dmu.dk

The problems concerning co-existence of genetically modified crops and organic or conventional non-GM farming are now brought much into focus in Denmark and elsewhere in Europe. Oilseed rape has been identified as one of the major crops, which will be most difficult to protect from contamination of GMO in the future (Eastham & Sweet 2002).

By computer modelling, NERI has made a so called meta-analysis in order to summarise the results from a number of field trials with oilseed rape in e.g. England, France, Australia, Canada, USA, Denmark and Sweden. In most of these trials (except Becker et al., 1992), herbicide resistance was used as a genetic marker and the results from these trials has been used to predict the similar gene dispersal from a GM field to an organic field of oilseed rape (for an overview of markers, see Kjellsson et al. 1997). The main questions, which were studied by modelling, are how the distance between fields affects gene dispersal and the effect of the field size on the total GM dispersal and the percentage of seeds containing GM. The pollen concentration of oilseed rape in the air normally decreases exponentially with the distance, but cross-pollination may also show irregular patterns depending on wind directions, topography and distribution of insect pollinators.

Results from the modelling show as expected a decrease of GM seeds in the receiver field with increasing distance to the GM field, which is particularly evident for small fields. Furthermore the results indicate that an increase of the size of the organic field has a relatively larger effect in reduction of the average GM-content than increasing the isolation distance. This effect is mainly caused by a dilution of the GM pollen by pollen from the receiving field. Other results from the study indicate that the use of a protective buffer zone is less effective in reducing the GM dispersal than an increased isolation distance. The results indicate that an isolation distance of 100 m will result in approx. 0.1 % GM content in the non-GM crop of oilseed rape if the field is at least 200 m wide. For small organic fields (width = 50 m), a low level of GM pollen dispersal (< 0.3 %) may be expected even with an isolation distance of 200 m.

There are a number of critical assumptions and restrictions, which affects these conclusions and may result in higher levels of gene dispersal than indicated by the model results. Hence, if the GM field is significantly larger than the organic field or if several GM fields are situated in the surroundings of an organic field, the extent of the GM dispersal will increase. It is also well known that pollen and gene dispersal may be irregularly distributed in the field, and that small pockets with higher concentration of GM-content can arise from this (important when monitoring). Furthermore, if hybrid varieties with male-sterile plants are cultivated in the organic field, the probability of GM pollination will increase depending on the percentage of male sterile plants. Finally, pollen dispersal from hybrids between GM oilseed rape and weedy relatives or from GM-volunteers in the surroundings has not been included in the model simulations.

In a current research project (http://www.darcof.dk/research/darcofii/vi3.html), NERI are also studying the extent of GM dispersal of pollen to organic and conventional fields of grasses and clover under different scenarios (e.g., the extent of GM farming, distribution of fields in the landscape, field sizes, etc.) and how this affects the possibilities for management and control. This includes development of a model of atmospheric dispersion based on biological and meteorological data and the location of cultivated fields.

Becker, H.C., Damgaard, C., & Karlsson, B. (1992) Environmental variation for outcrossing rate in rapeseed (Brassica napus). Theoretical and Applied Genetics, 84, 303-306.

Eastham, K. & Sweet, J. (2002): Genetically modified organisms (GMOs) The significance of gene flow through pollen transfer. Environmental Issue Report 28. European Environment Agency (EEA), Copenhagen.

Kjellsson, G., Simonsen, V., Ammann, K. (eds) (1997) Methods for risk assessment of transgenic plants. II. Pollination, gene-transfer and population impacts, Birkhäuser, Basel, 308 pp.