The News and Views article by Gray and Raybould(1) paints a rosy picture of the future of agricultural crops engineered with resistance to the herbicide glyphosate. It is true that the presence of the glyphosate resistance transgene (the EPSPS gene) in the chloroplast genome of crop plants would eliminate pollen transfer of this gene to weedy relatives. But there have already been large-scale releases of transgenic, glyphosate-resistant ('Roundup Ready') crops, including glyphosate-resistant Brassica napus (Canola, varieties Quest and LG3295), which is disturbing as there are many Brassica weeds that could potentially hybridize with the engineered B. napus (for example, see ref. 2).

Gray and Raybould(1) also say that "[glyphosate] tolerance in weeds does not seem to have evolved, despite extensive use of the herbicide for over 20 years". Although accurate about the extent of glyphosate use, this statement is inaccurate about the occurrence of spontaneous glyphosate resistance. There have been at least two reported cases of glyphosate resistance in Lolium rigidum (rigid ryegrass) in Australia. An article by scientists at Monsanto(3) cited by Gray and Raybould mentions one of these, stating that "studies are required to determine the basis of resistance". Monsanto, who produce a commercially available glyphosate ('Roundup'), are collaborating with a group at Charles Sturt University in New South Wales, Australia, to understand the nature of the resistance in this case. More information is available from a transcript of an ABC Radio National discussion (http://www.abc.net.au/rn/talks/bbing/bb970914.htm) and a catalogue of herbicide resistance (http://www.weedscience.com).

It seems foolish to assume that resistance to a herbicide with a single biochemical target in vivo would not develop, given time. Yet public concern about the ability of plants to develop resistance to glyphosate has been assuaged. Perhaps this has caused many other 'isolated' incidences of spontaneous glyphosate resistance to go unnoticed. We should all be concerned about the presumed increased use of glyphosate arising from the cultivation of transgenic glyphosate-resistant crops. It might be time to demote glyphosate from its status as a completely safe, fix-all herbicide.

References

1. Gray, A. J. & Raybould, A. F. Nature 392, 653-654 (1998).
2. Landbo, L. & Jorgensen, R. B. Euphytica 97, 209-216 (1997).
3. Bradshaw, L. D., Padgette, S. R., Kimball, S. L. & Wells, B. H. Weed Technol. 11, 189-198 (1997).