By Kevin M. Folta, Ph.D., Contributing Editor

Todays genetic engineering processes, especially those used on food crops, are the subject of much contentious debate. Much of that debate centers on the assertion that the process is unnatural" and therefore the result of the technology is inherently dangerous. Opponents use frightening images of Frankenfoods" and assert natural" heirloom varieties are the only plants man was meant to eat. In this four-part series, Kevin Folta, Ph.D., examines the development and uses of high-performance plants through the lens of science.

Part 2: It's All in the Genes

It is easy to forget that man has been manipulating plant genes for centuries through hybridization and selection. The process has been mostly blind to the genes themselves and instead focused on the traits they control; understanding the concept of genes is relatively new, but one discovered via plant breeding. In the late 1800s, a curious monk by the name of Mendel and some simple garden peas taught us there were inherent factors controlling inheritance of traits in plants, a discovery that would underlie the field of genetics.

The early 1900s introduced the practice of hybrid breeding. By 1930, hybrid-corn companies were producing inbred parent lines that, when crossed, produced outstanding products. Elite lines containing some positive characteristics were crossed with a different elite line bearing different ones. The result was a synergistic presentation of the best of both parents. Furthermore, the seeds from that hybrid could not be propagated and produce the same quality offspring, ensuring that companies who developed them could increase sales to seed new discoveries and improve plant quality.

New genes were also introduced by crossing elite lines with wild relatives with unusual characteristics. The work of Nobel laureate Norman Borlaug, Ph.D., used traditional breeding to convey new genes to known varieties, introducing superior traits that would heighten yields. This advance defined the Green Revolution, work that is estimated to have fed one billion people. Together, hybridization and introgression of wild genes induced a productivity spike in many agronomic crops. The increased productivity would only grow with successive rounds of intense breeding and improvement, augmenting yields, providing resistance to disease and producing better-quality products.

However, by 1980 it was clear that new strategies would be needed to sustain the rate of productivity. Breeders recognized that it is difficult to make a genetic cross to introduce a single trait from less-improved varieties. The valued trait has some genetic baggage, many additional genes, most of which dilute the desirable attributes of improved varieties. This effect is known as linkage drag, when genes physically close to the gene of interest travel along with it through breeding. The unavoidable problem of linkage drag introduces negative attributes to otherwise elite lines, adding significant cost, labor and time to the process of plant improvement through standard breeding. After all, it is hard to keep the genes you want and not pass on those that you dont. 

Traditional plant breeding can cause other issues, as well. Sometimes, when the priorities are to breed for the modern production environment, other important qualities are deprioritized and then lost. Nowhere is this more evident than in consumer sensory traits like taste and aroma. For decades, breeders have selected plants that had extraordinary yields, fruits that shipped well and lasted long. The genes controlling flavors were not a priority, and many were lost from cultivated varieties.

Check back tomorrow for Part 3: Transgenic Biotechnology

Part I: The Dawning of Crop Science

Kevin M. Folta, Ph.D, is an Associate Professor in the Horticultural Sciences Department, and Graduate Coordinator for the Plant Molecular and Cellular Biology program at University of Florida. He was the contributing author of the sequence to the strawberry genome and studies how genes and the environment work together to improve plant traits. He also has been recognized for his commitment to community outreach and student training in laboratory science. Contact him at [email protected] .