Dramatic reduction of crop-to-crop gene flow within a short distance from transgenic rice fields.

Genetically modified (GM) rice with enhanced agronomic traits and pharmaceutical uses are ready for widespread adoption. Little is known about isolation requirements for achieving stringent transgene confinement in rice. To investigate the extent of pollen-mediated crop-to-crop transgene flow, we conducted a field experiment with four plot-size treatments of adjacent GM and nonGM rice (Oryza sativa) in China. Three insect-resistant GM rice (Bt/CpTI) and nonGM isogenic lines were used in the study. The hygromycin-resistance transgene (hpt) marker was used to screen seeds from the nonGM rice rows at different distance intervals from GM rice plots. Based on the examination of > 2.1 million germinated seeds, we found a dramatic reduction in transgene frequencies with increasing distance from the GM crop, ranging from c. 0.28% at 0.2 m to < 0.01% at 6.2 m. In addition, different plot size did not significantly affect the frequencies of gene flow. In conclusion, pollen-mediated crop-to-crop transgene flow in rice can be maintained at negligible levels with short spatial isolation. The model can also be applied to other crops with self- and wind-pollination.