ACRE Advice

Advice of the Advisory Committee on Releases to the Environment under Section 124 of the Environmental Protection Act 1990

8 March 2002

Report on an article concerning gene flow from genetically modified maize to native (landraces) in Mexico

Background

ACRE was asked to review the study of Quist and Chapela ¹ concerning the detection of transgenic DNA in native maize (landraces) grown in remote areas of Mexico. The committee was asked to advise on the following issues:

1. Do the results reported indicate the detection of transgenes from transgenic lines of maize?
2. If so, how did this happen? In particular, is it likely that long distance pollination was the cause?
3. What are the implications of the findings for the separation distances in the UK maize farmscale evaluation programme?

Advice

The evidence for the presence of transgenes in landrace maize is not unequivocal. The data are derived entirely from the use of one type of PCR procedure, termed Inverse (I)-PCR. Additional data would be desirable to confirm the authors' conclusions for the reasons stated in ACRE's recent draft guidance document on the presentation of molecular data in submissions to ACRE to release GM plants to the environment ². This would include the use of alternative PCR procedures to verify the observations made, such as the design of primers specific to flanking sequences or the use of an alternative so-called "anchored" PCR method. In addition, the frequency of contamination implied in the report would suggest that non-PCR procedures such as Southern blotting could be deployed to verify the nature of the insertions and eliminate doubts concerning PCR artefacts.

Notwithstanding this point, the committee took the precautionary approach of assuming that the results did indicate the presence of transgenes in landrace maize and considered the mechanism by which this might have arisen.

Although a moratorium on the planting of GM maize in Mexico operates, there is no restriction on the importation of GM maize (mainly from the United States) for food use and the Mexican government distributes subsidised food throughout the country. The study reports that maize (samples K1 for example) obtained from local government stores contained GM kernels. It is customary for farmers in the region to save maize seed at harvest and mix this with "choice" seed from local markets before replanting the following season. In this way, farmers introduce (introgress) desirable traits into their local maize landrace seedstocks taking advantage of the fact that under these conditions cross-pollination is common.

The simplest explanation therefore, is that GM maize seed for human consumption has been transported to these regions by road (and by migrant workers returning from the United States) and that farmers have mixed the GM seed with the local seed for their crops. Introgression of transgenes into local landraces could have occurred by cross-pollination between genotypes within the field. This is a more likely explanation of the observations than long-range pollination in these remote regions of Mexico.

Therefore, this work does not have any implications for the separation distances used in the UK GM maize farmscale evaluation programme, though ACRE will be watching carefully for any further data from Mexico that can help to clarify the situation.

1 Quist, D. & IH Chapela. Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico. Nature 414, 541-542 (2001)

2 www.defra.gov.uk/environment/acre/molecdata/index.htm