Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2003
Publication Date: 7/1/2003
Citation: PEDERSEN, J.F., MARX, D.B. A TECHNIQUE TO REDUCE THE RISK OF GENE FLOW THROUGH SORGHUM POLLEN. CROP SCIENCE. 2003. Interpretive Summary: In the future, scientists may be able to improve many attributes of sorghum using genetic engineering. However, before such genetically engineered sorghum can be safely grown in the field, systems will have to be developed to prevent gene flow to weeds and non-engineered sorghum fields. It is pos- sible to greatly reduce the risk of gene flow from sorghum using currently available technology. Sorghum hybrid seed is currently produced almost exclusively on a cytoplasm, A1, that makes the lines male sterile. This has been successful because many lines, called R-lines, restore fertility to the progeny when used as pollinator to produce a hybrids. Sorghum hybrids can also be produced on an alternative cytoplasm, A3. However, few R-lines are known for this source of male sterility and resulting hybrids do not produce viable pollen. By converting transgenic lines and hybrids to A3 cytoplasm the risk of transgene escape through pollen can be significantly reduced. In commercial fields a small percentage of non-transgenic sorghum could be planted with the male sterile hybrids to provide pollen that would permit sterile hybrids to set seed, as well as provide in-field refugia. An experiment designed to test the efficacy of using A3 cytoplasm to reduce the risk of pollen flow from A3 hybrids under field conditions showed nearly zero seed set on fertile selfed F2 progeny (an indication of viable pollen) in twelve A3 sorghum hybrids.
Technical Abstract: A critical impediment to field testing and deployment of transgenic sorghum (Sorghum bicolor (L.) Moench) is the threat of gene flow to weedy relatives through pollen. A technique using sorghum with A3 cytoplasmic male sterility to control transgene flow through pollen while using non- transgenic pollinators is described. An experiment was designed to evaluate erisk of viable pollen flow using the technique under field conditions. Percent seed set under pollinating bags (an indicator of fertile pollen) was evaluated on selfed F2 progeny grown from open pollinated seed of twelve F1 hybrids produced in A1 and A3 cytoplasm. Seed was produced in hybrid yield trials in 1997 and 1998 at the University of Nebraska Field Laboratory in Ithaca, NE. Cytoplasm was nested within hybrid and four replications were used per year. Cytoplasm effects were highly significant, with seed set on A1 F2 individuals averaging 71%, and seed set on A3 F2 individuals averaging 0.1%. Percent seed set was nearly zero for selfed F progeny from all twelve A3 F2 hybrids. Upper confidence limits (P=0.05) for percent seed set were 6% or less for the progeny from all A3 F2 hybrids. These results indicate that gene flow through pollen can be severely restricted in sorghum.