Is there a risk that seed sterility genes could escape into wild populations and reduce their viability and long-term future? This is a point of considerable debate.
There is no publicly available literature which outlines quantitatively the risk or impact of transfer of TPS-related genes from transgenic crops to wild populations, although such trials have been conducted in the United Kingdom (EDF 1999).
The risk will vary depending on several factors including how closely-related the wild species are to the transgenics; the method of pollination (in-breeding or out-breeding); the location of the plants; the species involved and the distance between them. There have been several studies which have investigated the risk of gene-transfer through cross-pollination including Bergelson, Purrington & Wichmann (1998); Mikkelsen, Andersen & Jorgensen (1996); Arias & Riesberg (1994) and Evenhuis & Zadoks (1991).
Advocates of the Technology Protection System and other Genetic Use Restriction Technologies have consistently argued that the risk of ongoing gene transfer is negligible because TPS-pollinated plants will only produce sterile seeds and hence the gene will not be passed-on to other generations (Collins 1999).
Individual flowers that are not cross-pollinated with TPS pollen will still produce viable seed.
Monsanto (the owners of Delta & Pine Land Company since 2007) stated that one of the reasons for developing the technology was to ensure a “minimisation of outcrossing with related species” (Gupta 1998). Delta & Pine Land Company (2001) described the chance of transgene movement as being ‘remote’.
Rigel (1999) said that: “..one myth can be laid to rest: sterility does not spread. Planting terminator crops will not wipe out nearby plants…USDA touts Terminator as a means to prevent transgene escape and spread”.
There is, however a conflict-of-interest for the USDA because it serves as both a government regulator and investor in the technology (Ivins 1999).
Rakshit (1998) recognises there is a risk of gene flow between TPS crops and other adjacent plants, but that the sterility caused by it will prevent its further spread to later generations. Others such as Mellon (1998) and RAFI (2001c) have also expressed concern about gene transfer into wild populations. There is an acknowledged risk that a farmer who grows non-TPS crops beside one who does will have some of his seeds contaminated by the TPS crops resulting in a lesser viable seed count (Crouch 1998; Rakshit 1998; Gupta 1999). Goswami (1999) raised concern about the risk of cross contamination of traditional varieties with TPS crops.
Crouch (1998) raises another serious concern regarding the spread of TPS genes; that seeds which are not fully sterilised by the tetracycline may help spread other genes, such as that for glyphosate resistance. Crouch (1998) states that it is unlikely that 100% of seeds would be activated by tetracycline – some would escape – and that these seeds may germinate as “volunteers”, cross-pollinate with wild crops, and hence pass on the non-functional TPS gene and more importantly, the glyphosate-resistance gene (or whatever other genes have been inserted into the crop).
Pollen can travel a considerable distance and so contamination could potentially be widespread. In a study of gene flow between Helianthus spp., Arias & Riesberg (1994) found ‘wild’ plants of different species to contain genes which had been inserted into the cultivated crops up to 1 kilometre away. The greatest risk of gene contamination was for plants within a 3 metre radius. Arias & Riesberg (1994) found that distance alone was no barrier for gene flow.
Bergelson, Purrington & Wichmann (1998) found that in Arabidopsis, an inbreeding species, that plants were more likely to be pollinated by transgenic species containing a mutation, compared to non-transgenic species containing the same mutation. It is often thought that the risk of gene transfer in self-pollinating crops is negligible (Bergelson, Purrington & Wichmann 1998).