Pollen-mediated gene flow in maize tested for coexistence of GM and non-GM crops in the Netherlands: effect of isolation distances between fields

Abstract

In 2006 and 2007, field trials were performed to study the effects of the two isolation distances indicated by the Dutch Coexistence Committee, i.e., 25 m between GM (genetically modified) and conventional maize, and 250 m between GM and deliberately non-GM (e.g., organic) maize, on pollen-mediated gene flow (PMGF) under representative agricultural conditions in the Netherlands. Each isolation distance was tested at three different locations across the Netherlands in both years. For testing PMGF with the 25 m isolation distance, GM source fields of 100 m × 100 m (1 ha) were surrounded by four equally sized non-GM receptor fields at a distance of 25 m. For testing PGMF with the 250 m isolation distance, 1-ha GM source fields were surrounded by four 50 m × 50 m (0.25 ha) receptor fields in four different directions at 250 m. For the GM source field, the maize variety DKC3421YG containing the MON810 event was used with both distances. A maize variety near-isogenic to the GM variety was grown in the receptor fields to obtain good flowering synchronicity between GM and non-GM maize and thus optimal conditions for PGMF. Levels of the transgene in grain samples from the receptor fields were measured by a validated real-time PCR (polymerase chain reaction) quantification method for the MON810 event. Analyses showed the following levels of grain admixture as a consequence of PMGF, averaged over 12 fields for each isolation distance tested: at 25 m 0.084% (individual field averages ranged from 0.009%t0 0.296%) in 2006 and 0.080% (0.002% to 0.318%) in 2007, respectively, and at 250 m 0.005% (individual field averages ranged from o to 0.040%) in 2006 and 0.007% (0 to 0.037%) in 2007, respectively. Although weather conditions clearly differed between 2006 and 2007 (a hot and dry summer in 2006 vs. a relatively wet one with about-average temperatures in 2007), outcrossing rates did not differ significantly between these years.