A case study of GM maize gene flow in South Africa
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Date
2011
Authors
Viljoen, Chris
Chetty, Lukeshni
Journal Title
Journal ISSN
Volume Title
Publisher
Springer
Abstract
Background: South Africa has been growing first-generation commercial genetically modified (GM) maize since
1997. Despite a requirement for non-GM food, especially for export, there is no system for coexistence of GM and
non-GM crop. Gene flow is a major contributor to commingling, and different distances of cross-pollination have
been recorded for maize, using a variety of field-trial designs under different environmental conditions, with the
furthest distance being 650 m. However, these trials have usually been small plots and not on the scale of
commercial farming. There are also no published data regarding the extent of cross-pollination for maize in South
Africa, even after a decade of commercialization of GM. Thus, the aim of this study, conducted from 2005 to 2007,
was to determine the extent of GM maize cross-pollination under South African conditions in the context of
commercial farming practice.
Materials and methods: Field trials were planted with a central plot of yellow GM maize (0.0576 ha) surrounded
by white non-GM maize (13.76 ha), in two different geographic regions over two seasons with temporal and
spatial isolations to surrounding commercial maize planting. Cross-pollination from GM to non-GM maize was
determined phenotypically across 16 directional transects. Pollen counts during flowering were compared to
weather data as well as percentage cross-pollination. The data were transformed logarithmically, and mean
percentage cross-pollination was compared to high cross-pollination.
Results and discussion: Although there was a general congruency between wind data, pollen load and crosspollination,
it is evident that wind data and pollen load do not solely explain the directional extent of crosspollination
and that swirling winds may have contributed to this incongruence. Based on the logarithmic
equations of cross-pollination over distance, 45 m is sufficient to minimize cross-pollination to between <1.0% and
0.1%, 145 m for <0.1% to 0.01% and 473 m for <0.01% to 0.001%. However, compared to this, a theoretical
isolation distance of 135 m is required to ensure a minimum level of cross-pollination between <1.0% and 0.1%,
503 m for <0.1% to 0.01% and 1.8 km for <0.01% to 0.001% based on high values of cross-pollination.
Conclusions: Based on the results of this study, the use of mean values of cross-pollination over distance may
result in an underestimation of gene flow. Where stringent control of gene flow is required, for example, for non-
GM seed production or for GM field trials under contained use, the high values of cross-pollination should be used
to determine isolation distance. However, this may not be practical in terms of the isolation distance required. We
therefore suggest that temporal and distance isolations be combined, taking into account the GM maize pollen
sources within the radius of the most stringent isolation distance required.
Description
Keywords
Genetically modified foods -- South Africa, Corn -- South Africa, Gene flow -- South Africa, Corn -- Genetics
Citation
Viljoen, C., & Chetty, L. (2011). A case study of GM maize gene flow in South Africa. Environmental Sciences Europe, 23(1), 1-8.