Assessment of Real-time PCR Based Methods for Quantification of Pollen-mediated Gene Flow from GM to Conventional Maize in a Field Study

Abstract

Maize is one of the main crops worldwide and an increasing number of genetically modified (GM) maize varieties are cultivated and commercialized in many countries in parallel to conventional crops. Given the labeling rules established e.g. in the European Union and the necessary coexistence between GM and non-GM crops, it is important to determine the extent of pollen dissemination from transgenic maize to other cultivars under field conditions. The most widely used methods for quantitative detection of GMO are based on real-time PCR, which implies the results are expressed in genome percentages (in contrast to seed or grain percentages). Our objective was to assess the accuracy of real-time PCR based assays to accurately quantify the contents of transgenic grains in non-GM fields in comparison with the real cross-fertilization rate as determined by phenotypical analysis. We performed this study in a region where both GM and conventional maize are normally cultivated and used the predominant transgenic maize Mon810 in combination with a conventional maize variety which displays the characteristic of white grains (therefore allowing cross-pollination quantification as percentage of yellow grains). Our results indicated an excellent correlation between real-time PCR results and number of cross-fertilized grains at Mon810 levels of 0.1-10%. In contrast, Mon810 percentage estimated by weight of grains produced less accurate results. Finally, we present and discuss the pattern of pollen-mediated gene flow from GM to conventional maize in an example case under field conditions.

Regulating coexistence of GM and non-GM crops without jeopardizing economic incentives

“…First, by separating the inner parts of neighboring fields, pollen barriers act as an isolation distance, in turn increasing the distance GM pollen has to travel for cross-fertilization. Second, a pollen barrier -if the GM and non-GM crops in question are the same species -introduces competing pollen and/or can serve as a physical barrier to the flow of air and, consequently, the flow of pollen [16,[27][28][29][30][31]. Accordingly, a pollen barrier reduces the extent of cross-fertilization much more effectively than an isolation perimeter of bare ground of the same width [32,33].…”

Implementing isolation perimeters around genetically modified maize fields

“…However, defining the appropriate isolation perimeter width is complicated: various biological, physical, experimental and analytical factors with varying levels of importance play a role in the study of cross-fertilisation in maize (Devos et al, 2005). To take the factors that are relevant for co-existence into account, recent empirical crossfertilisation studies mimic worst-case commercial on-farm situations (Halsey et al, 2005;Della Porta et al, 2006;Goggi et al, 2006;Pla et al, 2006;Weber et al, 2007;Weekes et al, 2007). In Spain, out-crossing studies are even performed in real agricultural situations of co-existence.…”

“…Moreover, a maize barrier introduces competing pollen and/or may serve as a physical barrier to air and consequently pollen flow. As such, a maize barrier reduces crossfertilisation much more effectively than an isolation perimeter of bare ground of the same width (Della Porta et al, 2006;Pla et al, 2006). In recipient fields, the margins closest to the pollen donor could be harvested separately, and be discarded or be classified as 'GM maize' when the GM content exceeds the tolerance threshold.…”

Pollen from genetically modified plants in honey – problems with quantification and proper labelling

“…Real-time PCR quantifies GM DNA in the sample with respect to a species-specific reference sequence (Chouachi et al, 2008a;Chouachi et al, 2013). This technique was used for quantification of pollen-mediated gene flow from MON 810 maize to conventional maize (Pla et al, 2006) and to detect airborne MON 810 maize pollen (Kluga et al, 2012). However, real-time PCR cannot differentiate between a DNA sequence from GM pollen and a GM DNA sequence from other plant parts that can be present in honey.…”