Pollen‐mediated gene flow in maize in real situations of coexistence

Abstract

SummaryWe present the first study on cross-fertilization between Bt and conventional maize in real situations of coexistence in two regions in which Bt and conventional maize were cultivated.A map was designed and the different crops were identified, as were the sowing and flowering dates, in Bt and conventional maize fields. These data were used to choose the non-transgenic fields for sampling and analysis by the real-time quantification systempolymerase chain reaction (RTQ-PCR) technique. In general, the rate of cross-fertilization was higher in the borders and, in most of the fields, decreased towards the centre of the field. Nine fields had values of genetically modified organism DNA to total DNA of much lower than 0.9%, whereas in three the rate was higher. Some differences were found when comparing our results with those of common field trials. In real conditions of coexistence and in cropping areas with smaller fields, the main factors that determined cross-pollination were the synchronicity of flowering and the distances between the donor and receptor fields. By establishing an index based on these two variables, the rate of the adventitious presence of genetically modified maize could be predicted, as well as the influence of other factors. By applying this index, and in the case of a fully synchronous flowering time, a security distance between transgenic and conventional fields of about 20 m should be sufficient to maintain the adventitious presence of genetically modified organisms as a result of pollen flow below the 0.9% threshold in the total yield of the field.

Cross-fertilization between genetically modified and non-genetically modified maize crops in Uruguay

“…In Case 5, the area of GM-crop was six times smaller than the non-GM crop, and sowing dates had almost two weeks difference. Synchrony between flowering times seems to be a key factor for cross-pollination (Messeguer et al, 2006). In agreement with these previous studies, this research suggests that isolation by distance between crops or by the presence of physical barriers in between may quantitatively reduce cross-fertilization, but would not completely prevent it.…”

Effect of MON 810 cultivation and prevention to adventitious presence in non-GM fields: A case study in Slovakia

“…Chilcutt and Tabashnik (2004) reported that the pollen grains flow in Bt-maize was up to 31 meters. The results of Messeguer et al (2006) were more similar to ours, the authors concluded that the reliable distance between GM and conventional maize fields should be about 20 m to maintain the adventitious presence of GM maize as a result of pollen flow below the 0.9% threshold in the total yield of the field. Van de Wiel et al (2009) in the field trials in the Netherlands concluded that the grain admixtures as a consequence of pollen mediated gene transfer from GM maize were much lower: 0.080-0.084% at 25 m and 0.005-0.007% at 250 m, respectively.…”

Coexistence in the EU—return of the moratorium on GM crops?

“…Crossfertilization studies mimicking worst-case on-farm situations demonstrated that in many cases isolation distances exceeding 50 m are not necessary to comply with the tolerance threshold of 0.9% in grain maize [4][5][6][7] . Similar conclusions have been drawn from cross-fertilization studies performed under real agricultural situations in Spain 8 and from predictive vertical gene flow modeling at the landscape level in France 9 . Considering that cross-fertilization is only affecting maize kernels and that vegetative plant parts are unaffected, isolation distances for forage maize could be even shorter 6 .…”

“…Because such situations might not often arise in practice, fixed isolation distances can be unnecessarily conservative. In real agricultural conditions, fields are planted with GM and non-GM maize varieties with different sowing or flowering dates, and agricultural landscapes comprise a mix of maize fields, other crops and physical and/or natural barriers 5,8,10 .…”