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Potatoes as a renewable raw material

“The idea was to obtain more from the same land while using sustainable farming methods”

GM potatoes that produce cyanophycin, the raw material for a biodegradable plastic, in their tubers rot faster than conventional potatoes. The fear that they could survive for longer on the field has therefore not been confirmed. This is one of the findings of a biosafety research project that looked at potential environmental impacts of the cyanophycin potato.

Prof. Inge Broer, Chair of Agrobiotechnology, University of Rostock (Video clip in German)

GM potatoes on a trial field at the University of Rostock (2009)

For the rotting experiments the potato tubers are buried in the trial field

For the rotting experiments, potatoes were buried in sacks.

The GM potato tubers with the high cyanophycin content (left) rot faster than the unmodified conventional potatoes (right)

The potato was developed by scientists at the Universities of Rostock, Berlin, Bielefeld and Tübingen, optimised in greenhouse experiments lasting several years, and eventually tested in the field. For instance, the potatoes were tested to see to what extent plants can be used as safe production systems for bioplastics and other industrial raw materials. GMO Safety spoke to Inge Broer of the University of Rostock.

GMO Safety: Professor Broer, together with various other research bodies, you have developed a potato that provides the raw material for a biodegradable plastic. What kind of potato is it and what is its purpose?

Inge Broer: It is a starch potato that is normally grown to produce starch. We inserted a gene from cyanobacteria into this potato. They produce a substance that can be used as an alternative to hygroscopic polyacrylates, such as those used in cement or nappies. It can also replace phosphate in washing powder. So it is a substance that is needed in large quantities, but which is usually manufactured from petroleum. We can, however, also obtain it from bacteria or from these potatoes. Because of the genetic modification, the potatoes are able to produce relatively large quantities of the plastic.

GMO Safety: So the potato can be used as a kind of bioreactor to produce industrial raw materials. Does it make financial sense when compared with other methods, such as the use of micro-organisms?

Inge Broer: It becomes worthwhile when the plastic is obtained as a by-product. The potatoes are grown primarily for starch production and the potato waste can then be used to extract a substance that is much more expensive than the starch itself. When we obtain cyanophycin with the help of bacteria, we have to cultivate the bacteria by adding nutrients and energy, which costs time and money. With potatoes, this work is performed by the sun and the field and we don’t need a single extra square centimetre of land.

GMO Safety: Are there special risks associated with plants that produce industrial raw materials?

Inge Broer: No. You have to look at the risks for the individual trait and for the individual crop plant being used to produce these materials. You can’t generalise. The risks will vary depending on the transferred trait. You have to assess each one individually.

GMO Safety: What risks could be a factor in relation to the cyanophycin potato?

Inge Broer: The only thing we could imagine was that these potatoes might rot differently in the soil because their sugar metabolism has been modified. This is important for the rotting process.

GMO Safety: You conducted research both in the field and the laboratory. What did you do?

Inge Broer: After testing the plants for several years in the laboratory and in the greenhouse to observe their growth behaviour and to see how much of the biopolymer they produce, we wanted to know whether the rotting process really does differ from that of the conventional control potatoes that don’t produce this substance. So we sewed 30 potato tubers at a time into sacks – either the GM variety or the control variety – and buried them at different depths. The sacks had big enough holes to let in earthworms and other organisms. Then, in November, we started digging up the sacks again. Each month we dug up one sack of each variety and looked to see how the potatoes were doing. Were they rotting faster or slower? Were there the same number of earthworms? Were there other bacteria in the soil? What did the potatoes look like? What defence mechanisms were activated in the potato? How much tissue was still intact? What fungi were in the tubers? Were they different from the ones in the control potatoes? So we always compared the GM potatoes that produce the biodegradable plastic with the conventional potatoes from the same parent variety.

GMO Safety: What were the results of your three-year research project?

Inge Broer: We discovered that in terms of earthworms, bacteria and fungi the potatoes behave exactly like the control potatoes. We didn’t find any significant differences there. But the rotting speed correlates with the cyanophycin levels. In other words, if the potatoes produce a lot of this biopolymer, they rot faster than ones that produce little or none of it. It means that these potatoes do not survive as well in the field as the non-GM potatoes. So the probability of finding them as volunteers the following year is extremely small.

GMO Safety: The concept appears to work and you have assessed the potential risks. Are there economic prospects? Is there a chance that this potato will be placed on the market?

Inge Broer: The idea was to obtain more energy and more product from the same land while using sustainable farming methods. Good crop rotations are important for sustainable farming. A large number of crops in Germany have dropped out of the crop rotation because they are not financially viable. The additional production of this biodegradable plastic could make these crops economically attractive again and we could, for instance, establish sustainable crop rotations with nitrogen-fixing plants. That was the vision. That’s why we are also working on a large number of different crops that could be used in this kind of crop rotation. But at the moment I don’t see that we have a chance of bringing them onto the European market, even if the concept works extremely well in principle.

GMO Safety: Thank you for talking to us.

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