"Bt maize is an additional means of reducing mycotoxins."
Fungal diseases are a problem in maize and cereal cultivation. Not only do they cause yield losses, some fungi can also produce toxic substances. These mycotoxins contaminate food and feed products. GMO Safety discussed fungal infection in maize cultivation and different ways of controlling it with Prof. Andreas Schier of Nürtigen-Geislingen University.
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GMO Safety: Prof. Schier, you are concerned with fungal diseases in maize and the associated contamination of maize products with mycotoxins. The public generally does not seem to know much about this. Why are these mycotoxins a problem? Andreas Schier: Mycotoxins are harmful to humans and animals. There is more than one toxin, in fact there are a great number of them. There are over 300 different known toxins, each with specific effects. To give a few examples, zearalenones, a specific group of mycotoxins, can cause fertility problems. Fumonisin reduces the absorption of folic acid (vitamin B9), which is important for embryo development. Other mycotoxins which are absorbed via animal feed lead to fertility problems, causing fewer animals to be born. GMO Safety: In Central Europe maize is predominantly used as fodder. Are there noticeable effects on animals, when fodder maize is contaminated with mycotoxins? Andreas Schier: Certainly. Farmers who have problems in their livestock sheds are always sending us feed samples. Their animals often have fertility problems. In this case we very frequently find increased mycotoxin levels in the fodder. If it is replaced with a less contaminated fodder, the problems then generally disappear. Mycotoxins are clearly one of the causes, particularly those produced by a specific group of fungi, the fusaria. GMO Safety: Thresholds for some particularly dangerous mycotoxins have been in force in the EU since 2006, for both untreated maize after harvesting and for various maize products. In practice are these thresholds complied with even where there is severe fungal infection? Andreas Schier: Different expert bodies in Germany and throughout the world have been carrying out investigations for years. Fungal diseases are affected by many factors. For this reason it is virtually impossible to make general statements. We should certainly accept, however, that the recommendations and thresholds issued by the EU will be exceeded in certain years and at specific locations. GMO Safety: What individual factors cause an increased likelihood of fungal diseases? What can farmers do to overcome them? Andreas Schier: It is a very complex process. I will pick out just the key points. Definitely the weather conditions: humidity and high temperatures are conducive to fungal growth. These weather factors explain the fluctuations in mycotoxin levels in individual years. There are other factors as well, such as straw management. If the straw is left on the field after harvesting in autumn, it often leads to increased toxin levels in the subsequent generation. Soil management also plays an important role, for example mulch sowing and traditional plough sowing. Farmers can also prevent the risk of fusaria infection by choosing suitable, resistant varieties. Next point: a vigorous, healthy maize plant generally has low mycotoxin levels. In other words it should not be damaged or stressed and it should receive enough water. And one last point: the harvesting time: if a high level of fungal infection is expected in a high-risk year, the harvest should be brought forward to avoid exceeding the mycotoxin thresholds. But an early harvest often has financial drawbacks for the farmer. | |||||||||||||||||||||||
GMO Safety: You are also looking at Bt maize, which is not attacked by the corn borer because it is resistant. Consequently the plants have no grazing damage which would allow the fungus to penetrate. You are investigating in realistic conditions whether Bt maize and conventional maize plants have different mycotoxin levels. How have you designed the trials and what are your findings?
Andreas Schier: We are conducting various trials, for instance a long-term trial where we are growing successive maize crops on one field. In addition we are examining the effects of different types of soil management and looking at different weed control methods. For the different variants we also examine the maize plants for the presence of the three most commonly occurring toxins (see chart). Our results show a clear tendency: the variants in which we have very good corn borer control are the maize plants showing the least mycotoxin contamination. This applies to all three mycotoxin groups studied. We find the highest mycotoxin levels in the untreated variants. The levels are lower if the corn borer is controlled with insecticides, and we get the best effects by growing Bt maize.
GMO Safety: Is this result the same every year or does it depend on the pressure of infection from fungal diseases?
Andreas Schier: It is certainly not possible to specify fixed parameters that apply to every year. The prevailing weather conditions are a significant influencing factor, and they also affect the arrival of the corn borer. The results from 2007 indicate that we had a lower incidence of corn borers in many parts of the country. I expect that the mycotoxin concentration induced by them will also be lower. We had far more corn borers last year, and we saw significant effects on mycotoxin levels as a result.
GMO Safety: Similar studies have been carried out in other countries and by other working groups. How do your results compare with these?
Andreas Schier: Bt maize is grown in several counties in the EU, and here the results are similar to our own. To sum up, we can say that the mycotoxin levels are more or less halved in Bt maize compared with conventional maize grown on the same site without measures to control the European corn borer.
GMO Safety: Under which conditions does Bt maize cause a reduction in mycotoxin contamination in maize? Do we know enough yet to make specific recommendations?
Andreas Schier: It is fair to say that if a farmer wants to grow maize, particularly grain maize, in areas where the corn borer occurs, then Bt maize is a means of reducing mycotoxin levels in the maize plants. However, farmers should not ignore the other precautions I have mentioned for combating fungal diseases, such as agricultural methods and choosing appropriate varieties.
GMO Safety: So Bt maize is an additional means of combating mycotoxins, but no substitute for good farming practice?
Andreas Schier: Exactly. Farmers cannot completely avoid mycotoxin contamination resulting from a serious fungal infection just by growing Bt maize. All they can do is reduce it to a certain extent.
GMO Safety: Thank you for talking to us.
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