While ordinary people may not always understand the language associated with DNA research, the huge numbers that emerge from genetic studies conducted under a microscope are sufficient to impress anyone. So far, sugar beet tissue has revealed about 20,000 of what are called 'indicator tags' which represent some, but not all, of the 30,000 genes thought to make up the functional part of the sugar beet genome.

Controlling Genes

These indicator tags, individually, can then be connected with the possible traits they control to determine how the beet grows, its resistance to cold and disease, and the amount of sugar it is able to produce.

The official explanation goes like this: "We chop up sugar beet DNA and connect segments to bacterial plasmids that carry the DNA into (a safe strain of) E. coli bacteria, for storage," said J. Mitchell McGrath, a USDA Ag Research Service (ARS) geneticist. A slightly more understandable explanation states that each clone in the researcher's library of 38,400 cloned bacteria stores a different DNA sequence from the beet's genome.

Mitch McGrath, left, is holding a newly developed smooth-rooted sugar beet while technician Tim Duckert shows a traditional one.

Seedling emergence is one of the most important of those traits to sugar beet growers everywhere. As one grower put it, "If we don't get it out of the ground, it's no good to us." "One unique thing about sugar beets is that only about half of the seeds actually sprout," explained Paul Pfenninger of the Monitor Sugar Company in Bay City, Michigan. "Those tiny seedlings are exposed to everything from soil crusting to insects to disease to strong winds. A 40-mile-per-hour wind in that first month or so could wipe out a third of your seedlings. They're too delicate to withstand the sandblasting caused by strong winds carrying dirt particles."

Disease Resistance

But disease remains the main threat. Farmers rotate their beets with other crops, mainly corn, soybeans, and wheat, to avoid the disease buildup that can occur from growing beets in the same field two years in a row.

Working with two technicians and three graduate students, McGrath's team developed a test to show there are two genes needed for seedling resistance to disease. This will hopefully lead to disease resistant varieties of sugar beets.

After emergence and survival, the main concerns for sugar beets are yield and sugar levels. McGrath has found a possible marker to predict beets with high sugar content when they are about seven weeks old, instead of waiting for full growth at 25 weeks.

He believes beets with the highest sugar content aren't better at storing sugar, they are just better at keeping the sugar concentration high because they don't allow as much water in the beet. Beets with the most sugar tend to be smaller and less watery.

Mud on Beets

Another major industry concern is the tendency of wet soil to stick to sugar beets at harvest, where it is embedded in natural ridges. While processing shakes loose as much dirt as possible before weighing, growers must truck that soil back to their farms. This not only burns fuel, but can also spread disease as soil is moved from field to field. Soil removed in processing at a plant can cost the industry a lot of money. Monitor Sugar spends from one-half to three-quarters of a million dollars each year disposing of the soil in special storage ponds, then dredging the ponds when they become too full.

Research technicians harvest sugar beets and test sucrose content simultaneously.

The result of all this scientific effort is a new sugar beet germless with smooth roots that will cut soil loss and disposal costs by about half. ARS has already released sugar beet lines that combine smooth roots with high sugar content and resistance to rhizomania, a disease that appeared in Michigan for the first time last year.

That germless, done without molecular genetic tools, is symbolic of future releases envisioned, custom-designed sugar beets with more of what industry wants built into them. They will be assembled by a new kind of breeder who will be able to pull genes off the library shelf one gene at a time and combine them into new lines. Those sugar beet lines will be one of the eventual payoffs of the genetic revolution.