Coexistence in Maize: Effect on Pollen‐Mediated Gene Flow by Conventional Maize Border Rows Edging Genetically Modified Maize Fields

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.

Combination Approach of Border Rows and Isolation Distance for Securing Coexistence of Non‐Genetically Modified and Genetically Modified Maize

“…However, it has to be kept in mind that with the installation of border rows the total distance between donor and recipient field was increased by 9 and 18 m, respectively. In our previous study on border rows, we found no effect of a 9-or 18-m-wide non-GM maize border at the GM field edge when the distance between GM and non-GM maize field was constantly 51 m (Rühl et al, 2011). Empirical data obtained by this study, as well as our previous studies on coexistence in maize, therefore suggest that the total size of the isolation method (border row + isolation distance) is most important for the reduction of pollen-mediated gene flow in maize.…”

“…In our previous study on border rows, we found no effect of a 9-or 18-m-wide non-GM maize border at the GM field edge when the distance between GM and non-GM maize field was constantly 51 m (Rühl et al, 2011). However, it has to be kept in mind that with the installation of border rows the total distance between donor and recipient field was increased by 9 and 18 m, respectively.…”

“…In a previous study, we found no effect of a 9-or 18-m-wide non-GM maize border at the GM maize field edge when the distance between GM and non-GM maize field edge was 51 m, that is, the substitution of a part of the isolation distance by non-GM maize border rows had no significant effect on the GM content of the total harvest in comparison with the isolation distance alone (Rühl et al, 2011). It was supposed that the relatively large size of the gap between fields strongly influenced gene flow and reduced the border-row effect.…”

“…Published experimental-based evidence for the efficacy of non-GM maize borders at the GM maize field edge is still scarce (Rühl et al, 2011). Della Porta et al (2008 reported results of a 1-yr, unreplicated field trial showing some extent of reduced pollen-mediated gene flow by 12 rows of non-GM maize borders.…”

“…For example, in Slovakia, one border row can replace a 2-m isolation distance (Mihalčík et al, 2012), and, in Portugal, a 200-m isolation distance can be replaced by 24 border rows (De Fatima Quedas and Cruz de Carvalho, 2012). Even though the scientific indications for the efficacy of border rows are extremely scarce (Rühl et al, 2011), this measure fulfills the demand of non-GM maize growers as a coexistence measure that should be implemented by the farmer growing GM maize (Devos et al, 2009).…”