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In field trials, transgenes escaped from cultivated GM rice to its weedy and wild relatives.

Manipulated Organism: Cultivated rice (Oryza sativa).

Inserted Transgenes and Intended Effect: Bar gene to make transgenic rice resistant to the herbicide Basta (glufosinate ammonium). In this experiment herbicide-resistance functions as a marker for identifying the presence of the Bar gene.

Goal of This Study: Assess the gene flow between cultivated rice (Oryza sativa) and weedy rice (Oryza sativa f. spontanea), sometimes referred to as red rice, black rice or shattering rice, and between cultivated rice and perennial wild rice (Oryza rufipogon).

Results of This Study: Transgenic rice was co-planted with wild rice and with weedy rice in two study sites, in China and in Korea. Outcrossing (gene flow) was observed, and its frequency from transgenic cultivated rice to weedy rice varied between 0.011% and 0.046%. Outcrossing from transgenic cultivated rice to wild rice varied between 1.21% and 2.19%.

The authors point out that the seemingly small numbers should not be underestimated: In all cases where cultivated rice and weedy rice or wild rice flowered at the same time and plant heights were similar, outcrossing of the transgene did occur. In the study the data were collected from a limited number of plants over one generation only. Over many generations and in coexistence of weedy rice/wild rice with continued cultivation of transgenic rice, the transgene in the wild population could accumulate and increase.

Therefore the authors recommend not introducing herbicide-resistant rice into regions where weedy rice already is a serious problem, since through outcrossing weedy rice would become an herbicide-resistant "super weed."

Additional Comments: As the authors state, weedy rice and wild rice are commonly found where rice is cultivated. They coexist with cultivated rice in many Asian, African and American countries. Many of the wild relatives are highly compatible with cultivated rice. Flow of transgenes into wild rice populations and their persistence therein is therefore highly probable. If the transgenic trait also enhances the ecological fitness of the wild hybrid plant, which is the case when the herbicide is used, the potential damage to local ecosystems becomes great when the transgenes escape.

The authors further remark that these problems may increase with changing agricultural techniques. Traditional rice cultivation involves transplanting young plants into fields rather than direct seeding. In China, the transplanting technique is still widely used but there is a shift toward direct seeding. Where direct seeding is done, weedy rice becomes more frequent and can cause yield losses of up to 22%. A similar trend is occurring in Korea, where the loss in rice yield through weedy rice is estimated to be 5-10% of total rice production every year. As a review article states, "it seems extremely likely that new genes for herbicide resistance will spread to weedy rice, especially in regions where weed management is already difficult" (Lu and Snow 2005, p. 675).

The potential spread of the herbicide-resistance gene will likely increase even more, since the herbicide-resistance gene is used as a marker in other hybrid seed varieties.

Sources: Chen, L. J., D. S. Lee, Z. P. Song, H. S. Suh et al. (2004). "Gene Flow from Cultivated Rice (Oryza sativa) to its Weedy and Wild Relatives," Annals of Botany vol. 93, pp. 67-73.
Lu, B.-R. and A. A. Snow (2005). "Gene Flow from Genetically Modified Rice and Its Environmental Consequences," BioScience vol. 55, pp. 669-78 (review article).

Author Affiliations: Yeungnam University, Kyongsan, South Korea; Yunnan Agricultural University, Kunming, P. R. China; Fudan University, Shanghai, P. R. China.

Funding: NSFC for Distinguished Young Scholars, Shanghai Commission of Science and Technology, 211 project (Biodiversity and Regional Ecosafety).

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

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