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An empirical approach is given for specifying coexistence requirements for genetically modified (GM) maize (Zea mays L.) production, to ensure compliance with the 0.9% labeling threshold for food and feed in the European Union. Field data were considered in which pollen-mediated gene flow (PMGF) was measured within maize receptor fields at a series of distances from source fields having a marker. An empirical model is presented that fits the observed decrease of gene flow with distance. The model was parameterized to provide both reasonable worst case and expected case predictions of gene flow for various combinations of isolation distance, use of non-GM border rows in the GM field and/or separately harvested border rows in the receptor field. Based on the data assessed, the model is used to show that the effect of scale is minimal for source fields of surface area 4 ha and greater. Combinations of isolation distance and border rows of 20 m or more are predicted to result in gene flow of less than 0.9%, as a blended average for receptor fields 1 ha or larger. Lesser requirements are necessary when the source field is much smaller than the receptor, and an extension to the model is provided to estimate such effects. [ABSTRACT FROM AUTHOR]

An updated empirical approach is proposed for specifying coexistence requirements for genetically modified (GM) maize (Zea mays L.) production to ensure compliance with the 0.9% labeling threshold for food and feed in the European Union. The model improves on a previously published (Gustafson et al., 2006) empirical model by adding recent data sources to supplement the original database and including the following additional cases: (i) more than one GM maize source field adjacent to the conventional or organic field, (ii) the possibility of so-called "stacked" varieties with more than one GM trait, and (iii) lower pollen shed in the non-GM receptor field. These additional factors lead to the possibility for somewhat wider combinations of isolation distance and border rows than required in the original version of the empirical model. For instance, in the very conservative case of a 1-ha square non-GM maize field surrounded on all four sides by homozygous GM maize with 12 m isolation (the effective isolation distance for a single GM field), non-GM border rows of 12 m are required to be 95% confident of gene flow less than 0.9% in the non-GM field (with adventitious presence of 0.3%). Stacked traits of higher GM mass fraction and receptor fields of lower pollen shed would require a greater number of border rows to comply with the 0.9% threshold, and an updated extension to the model is provided to quantify these effects. [ABSTRACT FROM AUTHOR]