GM Seeds Could Beet Isolation Zones – But They Need Our Help

One of the potential risks associated with the wider release of genetically modified crops and their use in mainstream agriculture is the hybridisation of transgenic plants with their wild relatives. Previous studies on mechanisms for the escape of transgenic material into the wild population have focused on pollen dispersal as the main route, but new work by scientists at the Université de Lille in France to be published in Proceedings B, a Royal Society journal, highlights the role of seed dispersal – inadvertently assisted by human activity – in the potential wide scale dispersal of transgenic material with major implications for the siting of transgenic crops.

Sugar beet

“Gene flow and interbreeding from cultivated to wild plant populations has important evolutionary and ecological consequences,” says Dr. Jean-François Arnaud of the Laboratoire de Génétique et Evolution des Populations Végétales of Lille University. “This requires detailed investigation to assess the risk of transgene escapes into natural ecosystems.”

Sugar beets are of particular interest because they are cross compatible with their wild relatives, for example the sea beet, and crop-to-wild gene flow is likely to occur via ’’weedy’’ hybrid plants locally infesting fields.

“In our study we investigated the potential for ’’escape’’ of transgenic material by analysing a set of molecular markers in a population of weed beets within a field crop of commercially grown sugar beet, a natural coastal population of wild sea beet situated over 1.5 km away and a linking ’’contact zone’’ along a river where a possible mixture of wild and weedy beets could exist,” says Dr. Arnaud.
The experiment was conducted in the Wimereux area near Boulogne in Northern France.

Unexpected result

DNA from samples from plants harvested in the three areas was extracted and purified and individuals genotyped using eight molecular markers to establish the extent of gene exchange. There was clear evidence of weedy beets originating from the commercial crop field in the riverside ’’contact zone’’ some 1.5 kms away from the field.

“Contrary to classical expectations we found that gene flow through pollen was limited,” explains Dr. Arnaud. “However we found that weedy beets can act as a crop-to-wild bridge by escaping from commercial beet fields to wild populations via accidental seed flow. Our results highlight the likelihood for transgene escape resulting from seed dispersal events.”

Human culprits

Dr. Arnaud believes that the main mechanisms for seed flow in the studied area are human activities. “Accidental transport of seeds within soils carried on motor vehicles, or by other normal agricultural activities is the best explanation,” says Dr. Arnaud. “Our finding are consistent with the hypothesis of human-mediated long-distance dispersal.”

“Once wild and weedy beets have been brought close together by seed dispersal hybridization can occur by subsequent pollen dispersal,” continues Dr. Arnaud.

Two important implications arise from this work. “Firstly it reinforces the agricultural economic issues caused by increased invasiveness of any future transgenic weed beets within the agricultural system – originally highlighted by Benoit Desplanque and colleagues – and secondly it implies that we must be very cautious regarding the location of transgenic commercial sugar beet field,” concludes Dr. Arnaud. “If GMO sugar beets are established in regions where populations of the wild form also occur, then gene flow between wild and cultivated relatives is almost inevitable.”