Hybridization and the
Introduction of Transgenes into Wild PopulationsHybridization and the
Introduction of Transgenes into Wild PopulationsGene flow from crops to wild relatives can potentially influence characteristics of wild populations, yet little is known about this process. A new feature of crop-to-wild hybridization is that soon many crops will be dramatically improved by genetic engineering. When transgenic crops are grown near weedy relatives, fitness-related transgenes will be transferred to wild populations, perhaps causing them to become more invasive.
The major goal of my research is to determine how gene flow from a genetically engineered crookneck squash cultivar (Cucurbita pepo) affects the fitness of wild-crop hybrids. In particular, studies I have been doing test for a fitness advantage of tightly linked transgenes that code for resistance to two common plant viruses that often adversely affect squash plants. Seeds from a wild population in Arkansas were used in crosses with Asgrow's Freedom II transgenic crookneck squash (a PCR-based DNA marker has been developed to distinguish transgenic from non-transgenic progeny). Transgenic squash is the first "high risk" variety to be deregulated in the US, so it offers a unique opportunity to examine the evolutionary and ecological consequences for wild populations.
Under natural conditions, first-generation wild-crop hybrids (F1) will probably be relatively rare within wild populations, so most hybridization will involve wild plants as the recurrent parents. Therefore, in order to determine the possible effects of the movement (introgression) of a transgene into a wild population, F1 hybrids were crossed with purely wild plants to develop a "backcross" (BC1) hybrid generation. I hypothesized that transgenic BC1 plants would be more similar to wild plants in several fitness parameters than the F1 hybrids. Pilot experiments had shown that F1 wild-crop hybrids have lower fitness than wild plants. A field test in summer 1997 confirmed that BC1 plants are intermediate in fitness between wild and F1 plants and that further introgression is likely to occur.
A later field experiment in 1998 was designed to mimic a further generation of introgression by looking at the fecundity of BC2 plants. We planted the BC2 generation along with the other types described above at two agricultural field sites in Arkansas. Fecundity for wild plants was reduced during this season relative to the previous on, so that there were no statistical differences between wild, BC1, and BC2 plants at either field site. Heat and water stress were intense during this season, which may explain the difference in fecundity in wild plants. The results of this experiment suggest that fecundity differences may be dependent on climate and that, under the right climatic conditions, second generation backcross hybrids may be able to easily catch up to wild plants in terms of fecundity.
Last Updated: May 13, 2008