Locations, trial design, research questions and results

Research methods

Location and design of the trial fields:

The 2008 trials are taking place at six locations (Braunschweig, Dahnsdorf, Forchheim, Gross-Lüsewitz, Mariensee, Sickte). Mariensee is the main site. Two trial field designs have been set up at several locations according to a standard pattern. This will ensure that findings from individual locations are comparable and can be jointly evaluated.

Test systems: Two test systems are being used to determine the outcrossing rate. When developing measures which will be translated into good agricultural practice (e.g. separation distance), Bt maize will be used in principal as the pollen source (donor). Outcrossing to test fields with the isogenic variety (recipient) will be determined by genetic analyses. In parallel with this, coloured maize will be used as a GMO-free test system: individual yellow kernels appearing on the otherwise white maize cobs will provide a visual indication of outcrossing. Although this test system is cheaper, the results are not exactly comparable with current maize varieties due to the particular flowering features of the white maize variety. For this reason, it is only used when accompanied by comparative studies (e.g. the effect of different crop species planted between GM maize fields and conventional maize fields).

Sampling: Generally, twenty maize cobs are taken as samples from each of several points across the field and in some cases whole plants growing immediately beside the cob sampling points are also collected. This enables a comparison between silo and grain maize. All samples from the trial fields which use Bt maize as a test system are examined by an external laboratory.

Influencing factors: All the trial fields are equipped with weather stations which are operated by the German weather service and regularly evaluated. Wind direction, wind speed, temperature, air humidity, precipitation and sunshine are recorded on site during the flowering period. The outcrossing trials are conducted under worst-case conditions, i.e. the fields are arranged in the direction of the prevailing wind and varietal pairs (Bt maize and isogenic hybrid) with virtually synchronised flowering times are used.

Research questions and findings 2005 – 2007

In 2005 the trial designs and test systems were tested and evaluated for their suitability for coexistence studies. On the basis of these findings, further realistic field trials took place in 2006 and 2007.

Outcrossing distance: On the basis of literature studies, the minimum separation distance required to comply with the EU labelling threshold was originally set at 50 metres in 2003. In 2005 and 2006 various distances around this value were tested (24, 51, 78 metres). The trials, some of which were conducted when there was a constant prevailing wind, showed that significantly higher outcrossing rates than the threshold value can occur in the margins of the conventional neighbouring field even at a distance of 78 metres. However, outcrossing rates throughout the field at this distance were well below 0.9 percent.

In 2007 the distances were increased to 51, 78 and 102 metres and the results from these trials are currently being analysed.

Margin effects, in other words higher outcrossing rates at the field margin, also occurred over large distances in the outcrossing trials (2005, 2006). A single outcrossing was even found in the first field margin rows at a distance of 234 metres, although none were detected in the middle of the field.

In 2007 the 150 metre separation distance, which is now statutory, was tested for the first time. Here too there were margin effects, but outcrossing rates were very low and significantly below the EU labelling threshold across the field as a whole.

Intermediate crop: In 2005 a low-growing clover/grass mix was compared with tall sunflowers to investigate what affect the crop species planted between the maize fields had on the incrossing rate. It was found that sunflowers do not provide an effective physical barrier against pollen drift. The findings from this study have now been published in Crop Science, Vol.48, January-February 2008.

In 2006 the clover/grass mix was compared with cereal stubble. Because of their cultivation frequency, cereal crops are often grown between maize plots. Reliable results from this study are not yet available.