A case study of GM maize gene flow in South Africa

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.

Geostatistical Analysis of Quality Protein Maize Outcrossing with Pollen from Adjacent Normal Endosperm Maize Varieties

“…This was evident first from that, generally, plants at the edges of the QPM blocks, which by default were closest to the source of foreign pollen, exhibited the highest levels of outcrossing. Second, plants at the edges on the upwind side displayed higher levels of outcrossing than those on the downwind side as reported earlier by Langhof et al (2010a, b), Popescu et al (2010), and Viljoen and Chetty (2011). The variation in outcrossing from site to site and season to season, prevailing wind direction effects, and effects of synchrony of flowering and distance from the yellow source were previously reported by Haegele and Peterson (2007), Langhof et al (2010b), and Viljoen and Chetty (2011).…”

“…Several pollination studies have also been conducted to estimate the levels of outcrossing caused by transgenic crops using different approaches (Sears and Stanley‐Horn, 2000; Luna et al, 2001; Brookes et al, 2004; Haegele and Peterson, 2007; Langhof et al, 2010a, b; Viljoen and Chetty, 2011).…”

“…Several pollination studies have also been conducted to estimate the levels of outcrossing caused by transgenic crops using diff erent approaches (Sears and Stanley-Horn, 2000;Luna et al, 2001;Brookes et al, 2004;Haegele and Peterson, 2007;Langhof et al, 2010a, b;Viljoen and Chetty, 2011). Sears and Stanley-Horn (2000) reported that 84 to 92% of the Bt maize pollen fell within 5 m radius while 96 to 99% fell within 25 to 30 m and no pollen was found beyond 100 m from the fi eld.…”

Spatial and Temporal Assessment of Pollen- and Seed-Mediated Gene Flow from Genetically Engineered Plum Prunus domestica

“…Concerns related to pollen-mediated transgene flow (PMTF) generally center around issues of developing weedy variants of wild species due to the acquisition of transgenes, or loss of species diversity due to increased fitness of GE hybrids [5], [10], [15], [4]. The majority of PMTF studies have been undertaken on agronomic crops such as soybean [8], maize [13], cotton [14], canola [15], and rice [16], or on herbaceous horticultural crops including tomato, sugar beet, strawberry [17], Chinese cabbage [10] and summer squash [11]. While there have been reviews [18] and theoretical and modeling studies [9], [19], there are few reports documenting PMTF in tree species with the exception of citrus [20], apple [21], and papaya, which is a relatively short-lived herbaceous tree species [22].…”

Strategies for building trust with farmers: the case of Bt maize in South Africa

“…Good agronomic practices include the distancing of GM and non-GM crops physically and temporally, and planting refuge areas in order to prevent insect resistance build-up to transgenic crops such as Bt maize [17]. Refuge areas, or refugia, are the buffer zones of non-Bt maize (susceptible to stalk borers) planted in close proximity to Bt maize to provide a pool of stalk borers susceptible to Bt maize.…”