Will Non-Transgenic GM Plants Win Favour with Regulators and the Public?

The creation of transgenic plants often involves the use of DNA sequences from bacteria and other non-plant organisms – in particular as vectors to introduce the desired genes. However, some people are concerned about the use of DNA from such distantly related sources, and regulators require separate rules to be complied with for transgenic plants compared to those derived by selective breeding. Could using plant-derived sequences help address those fears and reduce the regulatory burden for crop biotechnologists? 

Tony Conner and his colleagues from Plant and Food Research, New Zealand consider the potential for intragenic vectors in a paper in CAB Reviews. This involves finding DNA fragments within a plant species that are very similar to those from foreign DNA that have been used as vectors for many years. Various techniques have been developed, some involving small amounts of foreign DNA, but fully intragenic plants have no foreign DNA and are entirely composed from plant-derived sequences. 

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Environmental impacts of Bt crops – on target or non-target?

Genetically modified crops containing a toxin gene from the bacterium Bacillus thuringiensis have been used by farmers for 11 years now. These Bt crops were designed to give the plants resistance to important pests. But might they also be harming non-target invertebrates?  A study by Steven Naranjo of the US Department of Agriculture’s Agricultural Research Service looks at the evidence and compares it with the impacts of the pesticides that would otherwise have been used.

Bt maize and cotton have been commercially produced on about 42 million hectares in 20 countries. Their potential non-target effects have been considered in over 360 published research papers. Naranjo, in his paper in CAB Reviews, looks across around 200 of these studies to draw conclusions.

 

Investigations found that the abundance of all non-target invertebrates was slightly lower for Bt crops than in non-Bt crops, but much higher in Bt crops than in non-Bt crops treated with insecticides. Using meta-analysis, a way of doing a meaningful comparison across different studies, Naranjo found that laboratory studies indicated negative effects of Bt on some non-target invertebrates, though these depended on how the trials were done and which invertebrates were being looked at. However, few harmful effects of Bt crops were shown in field studies. One factor may be that exposure to the Bt toxin is higher in the laboratory experiments than in the field. It was also clear that nontarget effects for insecticides are much greater than for Bt crops.

 

While Bt crops mean that some specialist parasitoids that would otherwise attack pests of maize have less to feed on, the overall levels of predation on pests have not been shown to drop. Naranjo believes Bt crops could enhance the role of biological control in integrated pest management.

 

Naranjo's paper emphasises that a key comparison to make is what would have happened without Bt crops. Bt maize and Bt cotton are believed to have led to a 136.6 million kg reduction in insecticide active ingredient, and rootworm-resistance crops will reduce the levels of insecticide present in the soil.

 

The paper, "Impacts of Bt crops on non-target invertebrates and insecticide use patterns" by Steven E. Naranjo appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2009, 4, No. 011, 23 pp.

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Why Can’t GM and Organic Just Get Along?

Growing of organic and genetically modified crops on neighbouring farms continues to be contentious, especially in Europe, but the issue of coexistence of same-species crops for different markets is not limited to GM. In a paper entitled “Can GM and organic agriculture coexist?”, Eberhard Weber points to the need for oilseed rape for cooking and industrial oil to be segregated, and similarly for crops for human food and animal feed for both maize and barley. Writing in CAB Reviews, he says that such situations work on the principle that some contamination will happen, but that “threshold values above zero for adventitious presence must be defined for coexistence rules.”

One company growing GM maize in Germany offered to buy maize from neighbouring non-GM farmers on the same conditions they would achieve without a GM neighbour. “The neighbouring farmers agreed, meaning that no coexistence problem arose,” says Weber, from Martin-Luther-University Halle-Wittenberg.

Weber notes that various organic organisations only require that the production process organic farmers use must not involve GMOs, rather than that they must ensure no GMO presence in their products. He quotes the International Federation of Organic Agriculture Movements: “Organic products are not defined as being free of unwanted pollution. Just as organic farmers cannot guarantee zero contamination from pesticides they do not use themselves, there is no way for them to guarantee that organic products will not be polluted by traces of GMOs.”

Weber looks at the various planting arrangements suggested to minimise gene flow to neighbouring fields. “Many experiments show that the GMO content is reduced with increasing distance as it should be, but no zero level can be achieved”. However, the variability of wind direction means no models can be entirely reliable.

As long as the same threshold value is valid for conventional and organic products, the GM farmer should not have to distinguish between neighbours with conventional and organic production, says Weber. ”The best way will always be agreement between farmers. As long as only farmers are involved, this can mostly be achieved.” However, he says that the involvement of other groups who try to influence political decisions on the rules make it difficult to predict the future of coexistence.

Can GM and organic agriculture coexist?”by  Eberhard Weber appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 072, 8 pp.

Can Bt Maize Beat Down Mycotoxins?

Bt maize (which contains a toxin gene from Bacillus thuringiensis) is genetically engineered to limit damage from certain insect pests. Fungal infestation, which leads to mycotoxin contamination, is known to follow pest damage. So can the Bt toxin also help by reducing mycotoxins in maize?

Felicia Wu from the University of Pittsburgh examines the sometimes conflicting evidence in a paper in CAB Reviews. Aflatoxin is the most serious mycotoxin in terms of financial impact, and it appears that levels of this toxin are not consistently reduced in Bt maize in comparison to non-Bt maize, although future Bt maize varieties may have a more positive effect. However, fumonisin, another important mycotoxin, is reduced in almost all studies. Fumonisin is associated with oesophageal cancer and neural tube defects. Reducing fumonisin through Bt could have significant benefits in developing countries, especially where unprocessed maize is a key part of the diet, and so mycotoxins are present at levels which can health problems. It also could help them avoid losses in the export market through rejection of contaminated maize.

The paper, “Bt corn and impact on mycotoxins” appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2007, 2, No. 060, 8 pp.