Aug 15, 2002

Research Projects

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Out-crossing from transgenic maize and quantifying outcrossing rates

(1999 – 2002) Federal Biological Research Centre for Agriculture and Forestry (BBA) (sice 2008 Julius Kühn Institute (JKI)), Institute for Plant Virology, Microbiology and Biosafety, Braunschweig

Topic

Transgenic maize outcrosses to neighbouring fields with non-transgenic maize plants as a result of pollen dispersal. The following questions were investigated under the realistic conditions of large-area cultivation:

• To what extent does the Out-crossing rate decrease with distance?
• How does the prevailing wind direction affect outcrossing?

The outcrossing rate was measured using both PCR techniques and special germination tests. Maize with a genetically engineered Herbicide Resistance was used in the trials.

A further aim of the project was to find realistic data relating to the outcrossing behaviour of maize. The data can be used as a basis for establishing suitable measures to avoid exceeding a specific threshold for admissible GMO content – for example adequate isolation distances between fields with transgenic and conventional maize.

Summary

Measurements taken in 2000 showed that the number of outcrosses decreased sharply with distance.

Outcrossing in the direction of the wind is almost twice as high as against the wind. Outcrossing shows a marked decrease over the first few metres, even in the direction of the wind.

The procedures developed to measure the outcrossing rate – PCR analysis and germination tests – have proved their practical suitability.

Experiment description

Experimental arrangement

A one-hectare plot of land in the centre of the experimental area was planted with transgenic herbicide-resistant maize. This was surrounded by a 5.5 hectare strip of non-transgenic maize. Maize was harvested and checked for outcrosses at increasing distances from the transgenic maize. Wind direction and speed were measured at the edge of the field.

The field experiments were conducted in 2000 and 2001. In 2001 the design of the field was modified. Additional plots of land were planted in the direction of the wind to investigate whether these plots reduce the outcrossing rate. Clover was grown between the plots.

Procedure for Detecting Outcrosses

The outcrossing rate was measured using a germination test and also using PCR analysis.

Germination test: The harvested grains are germinated in bowls. The seedlings are sprayed with the herbicide, so that only the herbicide-resistant plants survive. Each surviving plant represents an outcrossing event. Outcrossing rates of more than 0.5 percent can be reliably detected.

PCR detection: Flour ground from batches of 10,000 grains is examined. Characteristic DNA sequences from the transgenic maize are detected. Since a quantitative PCR technique was used, it is possible to make inferences about the proportion of maize grains with outcrosses. These techniques can be used to measure a GMO content above 0.1 percent.

Results

The results so far show that outcrossing decreases significantly with distance.

The average outcrossing rate is 1% just 10 metres from the plot with transgenic maize (see graph above).

At a distance of 25 metres values above 1% were recorded at individual measuring points. Past 50m the outcrossing rate remains below 1% in all cases.

Outcrossing in the direction of the wind is almost twice as high as against the wind. Outcrossing decreases significantly in the first few metres both in the direction of the wind and against it. At the field margin some outcrosses can still be detected but only in the direction of the wind. The investigation is not complete, since the statistically required number of grains has not yet been tested.

To deduce general laws for the outcrossing of maize, a mathematical model is to be developed in collaboration with Prof. Otto Richter of the Institute of Geoecology, Technical University of Braunschweig, on the basis of these results. As yet there is no recognized model for the dispersal of genetically modified maize under local climatic conditions. Such a model would be of great significance as the basis for protection concepts and cultivation recommendations.