Risk of Gene Introgression From Drought Tolerant Wheat to Jointed Goatgrass In the U.S. Great Plains.

Jointed goatgrass (Aegilops cylindrica Host) is a wild relative of wheat (Triticum aestivum L.) introduced into the western U.S. from Eurasia. The species is an agricultural pest that infests wheat fields causing economic loss. Common ancestry between the two species enables interspecific hybridization, providing a mechanism for the potential introgression of advantageous wheat genes to its weedy relative. Interest in the development of transgenic drought tolerant wheat cultivars has initiated concern for the potential for drought tolerance genes to introgress into jointed goatgrass. The risk of introgression is dependent on the rates of hybridization and recurrent backcrossing to the wild relative, the fitness advantage of gaining the gene, and the ability for the gene to spread across jointed goatgrass populations. Diversity within the species will determine if the risk is uniform or variable across the invasive range. Data from field experiments conducted on wheat by jointed goatgrass hybrids gave 95% confidence intervals for the rate of backcrossing to jointed goatgrass of 0.028 to 0.306% in 2008 and 0.077 to 0.604% in 2009. These rates correspond to the production of two backcross plants per hybrid plant. Two years of phenotypic field trials were also conducted comparing 30 western U.S. accessions of jointed goatgrass. The results show significant (P<0.001) variation in flowering time, plant height, tiller number, and spikelet number. A significant (P<0.0001) interaction between accession and environment was also observed. Together, our results indicate that in the Great Plains backcrossing occurs at a low rate, but that a field of hybrid plants could double its population size after one generation of backcrossing to the invasive species. Subsequent backcrossing would provide a mechanism for drought tolerance genes to introgress and spread to populations of the weed that are sensitive to drought stress, which as shown here, will vary across the western U.S.