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In the wild, resistance to herbicides might confer an advantage to plants.

Credit: Xiao Yang
One of the most common methods used to make crops more resistant to herbicides was found to offer advantages over weedy forms of rice. The results suggest that this modification could have positive effects on wild rice varieties and crop varieties.

A range of crop varieties have been genetically modified so that they become resistant to Roundup herbicide glyphosate. This resistance to glyphosate allows farmers to get rid of plants without doing any harm to their crops.

Glyphosate acts as an inhibitor of plant growth. It inhibits an enzyme called EPSP synthase. This enzyme is responsible in the creation of specific amino acids as well as other molecules. These substances can make up as much as 35% of a plant’s mass. The genetic modification method used for Roundup Ready crops by Monsanto (based in St Louis in Missouri) involves inserting genetic material into a crop to increase EPSP synthase production. Genes are usually derived from bacteria that cause disease to crops.

The extra EPSP synase allows for plants to resist the effects of glyphosate. Biotechnology labs also tried to make use of the genes of plants to boost EPSP-synthase levels, in part to take advantage of a loophole in the American system which permits the approval of regulatory authorities of transgenes not derived bacteria-based pests.

ラウンドアップ There aren’t many studies that have examined the possibility that transgenes like glyphosate-resistant genes could — after introduction to weedy or wild plants through cross-pollination increase the competitiveness of these plants in reproduction, survival and growth. ラウンドアップ Norman Ellstrand, a University of California plant geneticist, claims that, in the absence of selection pressure, any type of transgene is likely to create disadvantages in wild plants. The added machinery will lower fitness.

A new study, led by Lu Baorong, an ecologist from Fudan University in Shanghai, challenges that view: it shows that the weedy form of the common rice crop, Oryza sativa, gets an important boost in fitness due to glyphosate resistance, even when glyphosate has not been used.

In their study, which was published this month in New Phytologist 1, Lu and his colleagues modified the genetics of the rice plant to enhance the species’ own EPSP synthase. They crossed the modified rice with a weedy ancestor.

The team permitted the offspring from cross-breeding to cross-breed with each other to create second-generation hybrids. They were identical genetically with the exception of the amount of EPSP synthase genes they carried. The team discovered that the ones with more copies of the gene that encodes EPSP synthase expressed more enzyme and produced more tryptophan which is what we expected.

The researchers also found that the transgenic hybrids had higher rates of photosynthesis. They also produced more flowers and shoots and produced 48 to 125 percent more seeds than the non-transgenic hybrids -with or without glyphosate.

Lu believes that making the rice weedy less competitive might make it more difficult for farmers who have their land infested by the pest.

Brian Ford Lloyd, a UK plant scientist, said that the EPSP Synthase gene could get in wild rice varieties. This would threaten their genetic diversity, which is crucial. This is one of the clearest examples of extremely plausible harmful effects [of GM crop] on the environment.”

The general public believes that genetically engineered crops with extra copies or microorganisms genes are safer than ones containing only the genes of their owners. Lu states, “Our study shows this is not necessarily true.”

Researchers believe this finding calls for review of the regulations for the future on genetically modified crops. Ellstrand believes that biosafety rules may be relaxed because we can enjoy a high level comfort from two decades worth of genetic engineering. ラウンドアップ “But this study has shown that the new technologies still require careful evaluation.”