Rice is basically a self-pollinated crop, with limited degree of out-crossing (< 0.5 percent). The factors limiting the receptivity of rice flowers to out-crossing include a short style and stigma (1.5 to 4 mm in combined length), short anthers, limited pollen viability and brief period between opening of florets and release of pollen (between 30 seconds and 9 minutes). All wild and cultivated rice can also be wind-pollinated; however, rice pollen is short-lived with most pollen grains losing viability after approximately five minutes under typical environmental conditions.
Pollen viability is an important parameter that may affect gene flow frequencies at longer distances. As part of the characterization of GR2E Golden Rice to assess for potential unintended consequences of the genetic modification process, pollen morphology and viability were compared between GR2E and control rice. Morphologically, the appearance of pollen grains from GR2E and control rice was similar and there was no significant difference in pollen viability between samples obtained from GR2E and control rice. These data support the conclusion that pollen-mediated gene flow (out-crossing) from GR2E Golden Rice compared to conventional rice is unlikely to be changed as a result of altered pollen.