Unexpected diversity of feral genetically modified oilseed rape (Brassica napus L.) despite a cultivation and import ban in Switzerland.

Juerg Schulze,Tina Frauenknecht,Claudia Bagutti,Peter Brodmann,Zhong-Hua Chen

doi:10.1371/journal.pone.0114477

Abstract

Despite cultivation and seed import bans of genetically modified (GM) oilseed rape (Brassica napus L.), feral GM plants were found growing along railway lines and in port areas at four sites in Switzerland in 2011 and 2012. All GM plants were identified as glyphosate-resistant GM event GT73 (Roundup Ready, Monsanto). The most affected sites were the Rhine port of Basel and the St. Johann freight railway station in Basel. To assess the distribution and intra- and interspecific outcrossing of GM oilseed rape in more detail, we monitored these two sites in 2013. Leaves and seed pods of feral oilseed rape plants, their possible hybridization partners and putative hybrid plants were sampled in monthly intervals and analysed for the presence of transgenes by real-time PCR. Using flow cytometry, we measured DNA contents of cell nuclei to confirm putative hybrids. In total, 2787 plants were sampled. The presence of GT73 oilseed rape could be confirmed at all previously documented sampling locations and was additionally detected at one new sampling location within the Rhine port. Furthermore, we found the glufosinate-resistant GM events MS8xRF3, MS8 and RF3 (all traded as InVigor, Bayer) at five sampling locations in the Rhine port. To our knowledge, this is the first time that feral MS8xRF3, MS8 or RF3 plants were detected in Europe. Real-time PCR analyses of seeds showed outcrossing of GT73 into two non-GM oilseed rape plants, but no outcrossing of transgenes into related wild species was observed. We found no hybrids between oilseed rape and related species. GM plants most frequently occurred at unloading sites for ships, indicating that ship cargo traffic is the main entry pathway for GM oilseed rape. In the future, it will be of major interest to determine the source of GM oilseed rape seeds.

Highlights

Herbicide-resistant genetically modified (GM) oilseed rape (OSR, Brassica napus L.) is cultivated on a large scale in Canada, USA, Chile and Australia [1]
In the European Union, GM OSR cultivation is presently prohibited and authorization for the import for food and feed processing is confined to the GM OSR events GT73 (Roundup Ready, Monsanto), MS8, RF3, MS8xRF3 and T45 [11]
Johann station and the Rhine port of Basel showed different dynamics of GM OSR spread with new locations and new GM OSR events detected only in the Rhine port of Basel

Summary

Introduction

Herbicide-resistant genetically modified (GM) oilseed rape (OSR, Brassica napus L.) is cultivated on a large scale in Canada, USA, Chile and Australia [1]. Selection pressure provided by herbicide application increases the survival of herbicide-resistant transgenic plants potentially leading to an introgression of transgenes into related species [8, 9]. Another concern with respect to the cultivation of GM OSR is an unintended gene flow towards conventional or organic OSR crops which could lead to co-existence conflicts between different farming systems [10]. The feral GT73 OSR probably originated from spillage of conventional OSR seeds or other seed imports that were contaminated with GM seeds [19] At both sites, vegetation growth is controlled by regular glyphosate treatments. The selective pressure by glyphosate promotes growth of GT73 OSR and increases the escape risk of glyphosate-resistance transgenes through hybridisation and introgression into related species

Methods

Results

Conclusion