No abstract

The most reliable and practicable measure in assuring coexistence in respect to pollen‐mediated gene flow from genetically modified (GM) to conventional maize (Zea mays L.) is an isolation distance separating GM and non‐GM fields. Therefore, we tested distances between 24 and 102 m at three sites in northern Germany using a field orientation representing a worst case scenario concerning wind direction. During the 3 yr of field trials the highest levels of gene flow occurred at the site and year with the longest flowering synchrony and the strongest wind blowing constantly from the GM to the non‐GM field. It was shown that the GM content of a neighboring non‐GM maize field is mainly determined by wind speed and direction as well as by non‐GM maize field depth. Based on the maximum outcrossing data obtained it can be concluded that for non‐GM maize fields being 200 m deep or more an isolation distance of 50 m is sufficient to keep the GM content of the total fields grain harvest below the European Union (EU) labeling threshold of 0.9%. However, non‐GM grain maize fields with smaller field depth require larger isolation distances or additional coexistence measures. In most cases discarding 6 m of the GM maize facing non‐GM maize field edge has proven to be such a valuable measure. In silage maize production 50 m isolation distance is adequate even for non‐GM maize field depths down to 50 m. We recommend flexible separation distances in dependence on non‐GM maize field depth to comply with EU coexistence requirements.

One approach to ensuring coexistence of genetically modified (GM) and conventional maize (Zea mays L.) is reducing pollen‐mediated gene flow. Field experiments were conducted in 2005 at four sites in Germany to compare a tall sunflower crop (Helianthus annuus L.) vs. a short clover–grass crop (Trifolium pratense L. and Lolium spp.) with regard to their ability to reduce outcrossing when grown as buffer between pollen donor and recipient maize plots. Three different maize test systems were used: (i) quantification of a donor transgene via real‐time polymerase chain reaction (rt PCR), (ii) a nontransgenic test system based on a dominant kernel color trait, and (iii) a molecular marker test system based on rt PCR quantification of a cultivar‐specific nontransgenic DNA sequence. We found that the three test systems yielded comparable results concerning buffer‐crop effectiveness and edge effects. There was no difference in outcrossing rates when comparing the sunflower vs. clover–grass buffer crop. Outcrossing rates downwind beyond 12 m sunflower as buffer crop within adjacent 12‐m‐wide recipient maize were 4.2, 11.7, and 3.8% for the GM maize, the kernel color, and the molecular marker test system compared with clover–grass with 4.3, 9.6, and 3.6%. Pronounced edge effects were detected at the edges of recipient maize fields. Based on the present study, growing sunflower as a tall crop between GM and non‐GM maize cannot be recommended as an appropriate coexistence measure.

No abstract

In addition to or as substitution for a regulated isolation distance, conventional maize {Zea mays L.) border rows at the genetically modified (GM) maize field edge are considered as fea-ŝ ible measure to ensure coexistence between GM and conventional or organic maize. Therefore, we examined the effectiveness of 9-mand 18-m-wide non-GM maize borders at the GM maize field edge on outcrossing rates into a neighboring non-GM maize field. One field experiment each was conducted in 2008 at three sites in Germany using a field orientation representing a worst-case scenario concerning v\/ind direction. In each case, the distance between GM and non-GM maize fields was 51 m. Af two sites, sizes of GM and non-GM maize fields were 0.8 ha, respectively, and at the third site 0.5 ha (GM) and 0.3 ha (non-GM). The GM percentages of individual samples taken at recipient field depths between 0 and 90 m were quantified by real-time polymerase chain reaction. Overall, no pollen-mediated gene flow reducing effect of border rows was observed in the present study, although synchrony of anthesis between GM maize and border row maize was given at each site. Galculafed GM contents of the tofal non-GM fields harvest were always below the European Union labeling threshold of 0.9%. In consequence, planting 9-m-or 18-m-wide conventional maize border rows at the G M field edge is no reliable coexistence measure, at least if combined with an isolation distance.