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Unintended Effects of Genetic Manipulation
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Herbicide Resistance Passed to Weedy Rice
Craig Holdrege

Rice has been genetically modified to be resistant to the herbicide glyphosate (best known as Monsanto’s product “Roundup”). One of the weeds that is most problematic for rice farmers is “weedy rice” Oryza sativa f. spontanea), which is actually a subspecies of cultivated rice. So theoretically, by planting genetically modified (GM) rice and spraying glyphosate, farmers could rid their fields of weedy rice. But there’s a hitch in this neat picture.

Chinese scientists recently found that when they crossed a new type of glyphosate-resistant rice with its weedy relative, the resultant second generation hybrids “produced 48-125% more seeds per plant than nontransgenic controls in monoculture- and mixed-planting designs without glyphosate application” (Wang et al. 2013). Hybrids (in other generations as well) had higher concentrations of specific proteins and amino acids, increased photosynthesis rates, and they germinated more readily than nontransgenic controls. In scientific terms, the hybrids showed increased fitness.

Cultivated rice and weedy rice can easily form hybrids without human intervention. Therefore, by planting GM rice, farmers may unwittingly be helping weedy rice to spread rather than eradicating it! The GM-weedy rice hybrids may be more fecund than their cultivated and weedy ancestors, and as long as they maintain herbicide resistance they will be even harder to eradicate.

This possibility did not escape the researchers’ attention: “our findings indicate that if modified epsps gene is commercialized in cultivated rice without specific mitigation procedures, it may spread to weedy rice populations, persist, and increase in frequency, even in the absence of exposure to glyphosate.” The question is, whether there is any way in which the cross pollination of GM rice with weedy rice could be prevented. Plants in the field do not exist in a vacuum and pollen can travel far.

Wang, W. et al. (2013). “A Novel 5-enolpyruvoylshikimate-3-phosphate (EPSP) Synthase Transgene for Glyphosate Resistance Stimulates Growth and Fecundity in Weedy Rice (Oryza sativa) Without Herbicide,” New Phytologist. doi:10.1111/nph.12428
See also a commentary in Nature magazine:
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