Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 10/2/2007
Publication Date: 2/4/2008
Citation: Snow, A.A., Sweeney, P.M., Grenier, C., Tesso, T., Kapran, I., Bothma, G., Ejeta, G., Pedersen, J.F. 2008. Gene flow from sorghum to weedy conspecifics in Africa and the USA: implications for transgenic sorghum. Weed Science Society of America, February 4-7, Chicago, IL. Interpretive Summary:
Technical Abstract: Before transgenic sorghum is released to growers, regulatory agencies need to know whether transgenes are likely to spread to wild or weedy relatives of the crop. The long-term goals of our research are to evaluate whether transgene dispersal could result in worse weed problems with “shattercane” (Sorghum bicolor) in the USA, or conspecific wild sorghums in Africa. Here we describe three studies that provide baseline information about crop gene dispersal in sorghum. Given that sorghum often co-occurs with conspecifics, we used experimental plots and molecular markers to show that crop-wild hybridization takes place under field conditions in Ohio, albeit at low frequencies. Hybridization was detected in shattercane plants from Nebraska and in wild sorghum accessions representing S. bicolor subspecies verticilliflorum and drummondii from Sudan and Egypt. For the African genotypes, we also investigated the fitness of F1 crop-wild hybrids in common gardens located in Ohio, Indiana, and Niger to examine whether crop alleles can persist following hybridization. Crop-wild hybrids were vigorous and fertile, indicating that this generation can contribute pollen and seeds to subsequent generations. The relative fecundity of hybrids was fairly consistent across locations. For two accessions, crop-wild hybrids produced considerably more seeds per plant than the wild parent. For a third accession, hybrids produced similar numbers of seeds per plant as their wild parent. This study shows that selectively neutral or advantageous crop alleles are expected to persist in wild sorghum populations following hybridization. A third component of our research involved studies of the population structure of weedy shattercane populations in Nebraska, USA. We surveyed 11 populations using six microsatellite markers to examine the likelihood that crop genes could spread easily among populations of this self-compatible species. F-statistics and current migration rates estimated by assignment methods suggest that little gene flow has occurred among these populations. Therefore, the spread of fitness-enhancing transgenes or other crop alleles may be rapid within populations and slow among populations, depending on their proximity to cultivated sorghum and seed-mediated gene flow. These results can be used to model the process of crop allele introgression. Before transgenic sorghum varieties are grown in the vicinity of its wild conspecifics, consequences of crop-to-wild gene flow should be examined on a case-by-case basis, taking into account the transgenic traits involved and their ecological and agro-economic effects.