Humans have been genetically engineering agricultural crops ever since plants were domesticated. Notice the difference between maize and teosinte. Or how about what we have done to create modern
wheat. By either imposing an artificial selection pressure on a few important loci (in the case of maize) or encouraging larger, polyploid individuals (wheat), we have been manipulating the genome of plants for a long, long time. More genetic manipulation of agriculture below the fold.
The difference between the genetic engineers of yore and those of today are the tools at their disposal. The molecular revolution of the past few decades has led to faster mechanisms for manipulating genomes. It all began with selective breeding of individuals with favorable characteristics — ie, larger fruits, increased milk production, etc.
Another simple trick involves crossing your strain of interest with another strain that has some property that you would like in your strain. For example, say your favorite tree species has been devastated due to an invasive pathogen, but a related species from the pathogen’s native habitat carries one or multiple resistance genes. If you can cross the two species, you can select hybrids that are resistant to the pathogen. In order to recover the traits characteristic of your species, you will then backcross the hybrids to your species, again selecting for resistant individuals. You will continue these backcrosses for multiple generations until you have created a resistant strain of your species. The goal in these hybrid backcross projects is to introgress the resistance genes (and only the resistance genes) into your species from the other species.
While the traditional approaches work, they can be extremely time consuming. That’s why scientists are looking more and more towards using molecular tools to genetically engineer agricultural plants and animals. Grape wine cultivars have been bred for many generations to produce certain flavors and aromas in the finished product. If a certain strain of grapes are susceptible to a pathogen, viticulturalist are tentative to perform hybrid backcrosses to transfer resistance genes from another strain for fear of losing the characteristics that give those grapes their desirable properties.
A group at Missouri State University is working to characterize genes in American grape varieties that make them resistant to fungal infections. They plan to transfer those genes into European strains so that they can be grown in the humid Midwestern climate. Missouri’s not exactly a hotbed for wine production, but that could change if the vineyards are able to produce grapes that can tolerate the new environment.