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Chinese scientists have inserted scorpion and moth genes into oilseed rape (canola) plants to make them poisonous to insects feeding on them.

The researchers say that using two foreign genes at the same time means insect pests will be less likely to develop resistance to the genetically modified (GM) plants. The findings were published online in Plant Cell Report on 19 July.

The researchers tested the GM plants by exposing them to caterpillars of the diamondback moth (Plutella maculipenis). All of the plants showed some defense against the caterpillars, although the extent of this varied from plant to plant.

The caterpillars, which are major crop pests in parts of Africa, Asia and Latin America, have developed resistance to several available pesticides. There are also reports they are becoming resistant to 'Bt' plants, which are genetically modified to produce a toxin that kills insects but is harmless to birds and mammals.

The Chinese team, led by Jingxue Wang of the Agri-Biotechnology Research Centre of Shanxi Province, inserted two genes at once to overcome this problem.

The gene from the Asian scorpion (Buthus martensii) produces a poison that specifically affects insect nervous systems, leading to paralysis. The gene from the tobacco hawkmoth (Manduca sexta) produces a chemical that breaks down chitin, a major component of insects' outer surface and gut lining.

Because it is unlikely that a caterpillar would be able to resist both toxins at once, the researchers say their approach could slow down and minimise the chance of an insect developing resistance to the plants.

They also suggest using their approach in combination with the Bt toxin genes already widely used.

Lead researcher Wang, told SciDev.Net the team is trying the same combination of genes in GM cotton.

Eric Messens, a professor of plant molecular genetics at Flanders Interuniversity Institute for Biotechnology at Ghent University, Belgium, warns however that some scorpion toxins previously thought to affect only insects can also affect mammals.

He told SciDev.Net that detailed studies must be conducted to see whether the toxins produced by the GM plants affect human health.

Another concern about GM oilseed rape is that insects or the wind could carry pollen with foreign genes into non-GM oilseed rape crops or related species.

"Discussions about biosafety should be based on the results of practical case studies and not on worst case scenarios," says Gerhard Schwarz, a researcher at the Germany-based EpiGene company.

Schwarz and colleagues published a two-year field study of GM oilseed rape online in the European Journal of Agronomy on 21 June.

The team found that genetic contamination of non-GM plants with GM genes could be kept below the 0.9 per cent level required by European food labelling rules, without limiting the distance between the two sets of crops.

"Our results showed that the gene flow by pollen dispersal can be brought under control and does not lead to a biological catastrophe," Schwarz told SciDev.Net.

GM crops can therefore co-exist with conventional and organic farming, he added.

Link to abstract of paper in Plant Cell Report

Reference: Plant Cell Report doi:  10.1007/s00299-005-0967-3

Link to abstract of paper in European Journal of Agronomy

Reference: European Journal of Agronomy doi: 10.1016/j.eja.2005.04.002

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