GM oilseed rape: pollen dispersal and outcrossing

"It all depends on whether the new traits confer an advantage."

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Against the background of the possible cultivation of genetically modified plants, British agro-ecologists have produced a study on outcrossing behaviour for the European Environment Agency (EEA). The statements in the study that relate to oilseed rape in particular have been seized on by GM opponents as further evidence that the environmental risks of genetically modified plants are not controllable.

GMO Safety spoke to Dr. Jeremy Sweet from the National Institute of Agricultural Botany (NIAB) in Cambridge, one of the two authors of the EEA study.

GMO Safety: In Belgium a few field trials of transgenic oilseed rape have had their approval withdrawn in view of the risk of outcrossing . Your EEA report was cited in this context. Greenpeace too is demanding a ban on the deliberate release of GM rape. The environmental organisation categorises genetically modified oilseed rape as high-risk, because its genes transfer easily to other plants, and regards this, amongst other things, as a threat to species diversity. Is transgenic rape dangerous?

Sweet: Transgenic oilseed rape is not classed as a ‘high-risk plant’ in the EEA report; the report simply states that with oilseed rape there is generally a high risk of gene transfer via pollen dispersal. In other words, the likelihood of oilseed rape genes reaching other closely related plants is high in comparison to other crops. But this does not mean that adverse effects on the environment, i.e. a direct threat, can be deduced solely on this basis.

"It is the effect, not the frequency that is decisive."

GMO Safety: When can a genuine environmental problem come about as a result of pollen transfer? Sweet: The frequency of gene transfer via pollen dispersal is not critical. The question we should be asking is how the transferred genes behave and what effect they have in the other plants, in other words, the consequences of gene transfer to other plants must be taken into account; this is the decisive factor in safety assessment.

GMO Safety: Which wild plants is oilseed rape particularly good at incrossing to?

Sweet: We have discovered that rape can cross with two wild species in particular, turnip rape and wild radish. Studies in France have shown that hybrids produced as a result of cross-fertilisation between rape and wild radish survive for only a few generations. Incompatibility subsequently builds up in these plants and pollen and seed production falls. The plants eventually dwindle away. Introgression of rape genes into the wild radish population is therefore unlikely to occur.

"Crossings between oilseed rape and wild radish survive only a few generations."

GMO Safety: And how does it behave with turnip rape as a crossing partner? Sweet: Studies in Denmark and Britain have been able to show that gene flow from oilseed rape to turnip rape is relatively common. Further studies are needed to discover the consequences of gene flows from transgenic rape, in other words what effect the foreign genes have in the turnip rape.

GMO Safety: In your view, which transgenes are particularly critical and must be used with caution in oilseed rape plants?

Sweet: Genes that can make the oilseed rape more robust. Some pest- and disease-resistance genes could have this effect. But it all depends on whether the new traits actually confer a survival advantage on the plants. We are currently looking at factors that determine the survival and propagation of oilseed rape and turnip rape. These plant species are inherently not very robust compared with other plant species. They are referred to as ‘pioneer plants’, which are only able to persist for any length of time on disturbed land. Only major modifications to the characteristics of these plants can fundamentally change this situation. Then oilseed rape and turnip rape could possibly become established in specific ecological niches. In this context we are looking at what happens when insect- and fungus‑resistance genes enter wild populations. We simulate and model this situation with non-GM rape and turnip rape.

The final results of these investigations have not yet been published. However, it is evident that other factors such as grazing by snails, pigeons or other wild animals are critical in limiting the colonisation and spread of wild rape and turnip rape. Competition from other plants also prevents these plants from spreading unchecked.

"One can assume that herbicide-tolerant turnip rape will behave exactly the same way."

In addition, extensive studies in Britain have shown that herbicide-tolerant oilseed rape has no greater fitness or aptitude for colonisation outside the fields treated with the herbicides. It can be assumed that herbicide-tolerant turnip rape will behave in exactly the same way. We plan to carry out similar work on transgenic plants at a later date.

GMO Safety: In your report you conclude that, following the commercialisation of transgenic oilseed rape with different herbicide resistances , plants containing multiple herbicide resistances will emerge as a result of pollen transfer. Will it become much harder for farmers to control ‘volunteer rape’ (1) as a result of this, and will larger quantities of herbicide be needed to control multi-resistant rape plants in the following crop?

"Farmers must know exactly which herbicide to use."

Sweet:No, we can't assume that. We have been producing genetically modified oil seed rape plants with these multiple resistances here for years. What we have noticed is that even multi-herbicide-tolerant oilseed rape plants can be controlled effectively using normal crop rotations and standard commercial herbicides. What will become important is that the farmers learn how best to manage the available herbicides. They must know exactly which herbicide to use to control the herbicide-tolerant volunteer rape in question. Just as they do now with conventionally produced herbicide-tolerant weeds. If we grow these plants commercially in the future, we will have to ensure that programs are developed at the same time to better educate farmers in terms of herbicide management and to provide advice as well. GMO Safety: Dr Sweet, thank you for talking to us.

(1) Volunteer rape: oilseed rape produces large qualities of seed, some of which falls to the ground before or during harvest and remains in the field. The seed remains viable for over 10 years. When different crop species are grown on the same land the following years, the rape plants growing there must be controlled as weeds.

 

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