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