Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/6/2003
Publication Date: 7/1/2003
Citation: Gealy, D.R., Mitten, D., Rutger, J.N. 2003. Gene flow between red rice (Oryza sativa) and herbicide-resistant rice (O. sativa): Implications for weed management. Weed Technology. 17(3):627-645. Interpretive Summary: Red rice is a troublesome, and essentially uncontrollable weed of rice in the southern U.S., in part, because it is the same species as rice. Newly developed herbicide-resistant rice varieties in combination with the appropriate herbicide can now control red rice. This technology raises biosafety concerns because, under some conditions, herbicide resistance can nbe unintentionally transferred from the rice variety into red rice through cross-pollination. The ability of rice and red rice to cross-pollinate and the eventual flow of herbicide-resistant genes into red rice populations could reduce the effectiveness of this technology unless it can be managed properly. Outcrossing rates between rice and red rice are naturally low, but can vary widely. Therefore, successful herbicide-resistant rice systems will require careful management that includes using rice varieties that do not flower simultaneously with red rice, and crop/herbicide rotations that reduce long-term survival of any herbicide-resistant red rice that may be formed.
Technical Abstract: Red rice (Oryza sativa L.) has long been a troublesome, conspecific weed of cultivated rice (Oryza sativa L.). Herbicide-resistant varieties now offer new options for red rice control. However, this herbicide resistance can be unintentionally transferred to red rice through cross-pollination. Natural outcrossing among rice plants is generally low. The rate of outcrossing and subsequent rates of introgression of herbicide-resistance genes into red rice populations are likely to influence the success herbicide-resistant rice technology, because the ability to survive herbicide application is a strong selective advantage for hybrids and their offspring. Previously published studies indicated that rice X rice outcrossing rates were less than 0.5%. Preliminary microsatellite marker evidence from field studies in Arkansas indicates that red rice X herbicide-resistant rice outcrossing rates were 0.05% or less. However, outcrossing rates of 1 to 7% between rice and red rice have been reported previously, indicating that natural outcrossing rates probably vary widely. The well-established principles of weed resistance management appear to be relevant for herbicide-resistant rice systems and should be used in combination with avoidance of coincident flowering to mitigate the potential impact of gene flow from herbicide-resistant rice into red rice.