Co-existence without isolation distances?

Joachim Schiemann is co-ordinator of the Co-Extra work package “Biological approaches for gene flow mitigation”. Schiemann conducts biosafety research at Germany’s Federal Biological Research Centre for Agriculture and Forestry (BBA) and has been studying the out-crossing of transgenic plants with conventional crops for more than five years.

Dr. Joachim Schiemann co-ordinates the Co-Extra research on gene flow mitigation.
Dr. Joachim Schiemann co-ordinates the Co-Extra research on gene flow mitigation.
Dr. Schiemann, what are the main goals of your research project?

The goal is to develop pragmatic and practical solutions for the co-existence of agricultural practices using or not using genetically modified plants (GMPs). At this time, GMPs are being grown in Europe to a limited extent in only a few countries. But particularly with GM maize, a significant increase in plantings is expected in the next few years. It’s for this reason that we need to develop cultivation practices to reliably manage unwanted out-crossing into neighbouring fields. In that way we can protect consumers’ freedom to choose between GM, conventional, and organic foods. Farmers also have much to gain from reliable cultivation practices for co-existence. The resulting guidelines will help to prevent economic losses incurred by conventional farmers whose harvest would require labelling because of unwanted cross-pollination with GMPs – which in most countries has to be paid for by the farmer growing the GM crop.

What are the intended methods to facilitate the co-existence of various cultivation systems?

Our work package deals with male sterile maize, tomatoes, and sunflowers. Male sterile plants are unable to produce pollen, which prevents them to pollinate plants on neighbouring fields. We are also working on rapeseed lines with a feature known as cleistogamy, which means that their flowers do not completely open. Cleistogamy might be a successful way to keep GM rapeseed pollen from reaching conventional plantings. Finally, we’re looking into an alternative way of introducing foreign genes into plants. Instead of the usual procedure to introduce foreign genes into the cell’s nucleus, other DNA containing organelles can also be targeted for genetic engineering. When foreign genes have been introduced into the plastid genome, the plant’s pollen is usually transgene free. 

This sounds like promising options. Why can’t plants like these be put to use right away?

We first have to make sure that male sterility and cleistogamy remain stable under real field conditions and that those plants don’t release pollen under certain climatic conditions. And we have to study whether male sterile or cleistogamous crops perform well for farmers. For instance, their yield must match up to high performance varieties grown today – otherwise, they would never be welcomed by farmers. For these studies, ring trials are performed in Bulgaria, France, UK, Germany, and Switzerland.

How would male sterile plants be able to yield a harvest? Maize, for example, requires adequate pollination in order to produce kernels.

We plant a mixture of male sterile, genetically modified maize and pollen-producing conventional maize in one field. The pollen-donor plants provide about 20 percent of the total planting, allowing the entire field to be pollinated and set seed.

So when will these new approaches be made available to farmers?

State of the art predictions are impossible. If everything goes well and we will get positive results, male sterile GM maize, for example, might be available for planting in about five years. Whether this tool will be used to help solving co-existence problems, in combination with which traits and under which circumstances will be a matter of future discussion.

What can be done in the meantime? After all, GM maize is already grown commercially.

With that in mind, we are evaluating data on pollen movement from the literature that’s already available and conducting a few experiments of our own. This data is being used to create simulations of how pollen movement and out-crossing occur under a wide range of agricultural conditions. In fact, GM crop contents in conventional fields below the 0.9 percent labelling threshold depends on more than just separation distances. The size, shape, and orientation of fields also play an important role. In addition, the plants growing on the buffer strip separating two fields also have an effect on out-crossing. We will get a more detailed picture during the next years.

Based on the data you have available today, how much distance is necessary between fields to reduce out-crossing to an acceptable level?

The literature that we’ve studied for maize suggests that 20 to 25 metres will be enough. Some recent findings from Germany, however, suggest that depending on wind conditions, distances might have to be wider than this. That could be as much as 50 metres.

Is maintaining separation distances enough to secure co-existence?

For many regions in Europe, keeping minimum separation distances will be a practical way to achieve co-existence. There might be cases, however, where separation distances alone do not provide a practical solution. In some regions, the average field size is below one hectare. In those small fields, the GM content might exceed the EU threshold for labelling. When a wider buffer strip is needed to separate a small non-GM field from a larger GM field, the economic advantage of planting the GM crop might be lost.

Then what are the prospects for co-existence in regions with small field sizes? Will farmers in those regions simply have to refrain from planting GMOs in the long term?

Those regions might need more effective ways of preventing out-crossing. Biological containment tools like male sterile or cleistogamous plants, which I mentioned before, might potentially offer a middle-term solution. The future will show whether such solutions will be practical and economically feasible.

Dr. Schiemann, thank you for your time and input.