New Breed of Beet Geneticists
Shows How Sweet It Can Be
Geneticist Mitch McGrath (left)
discusses differences between
smooth-root and traditional
sugar beets with technician
J. Mitchell McGrath may not seem the man to be cast in
the role of a revolutionary. But he is part of a new guard of younger
geneticists at ARS who are leading
a genetic revolution in the sugar beet breeding industry. It began 10
years ago, according to Thomas K. Schwartz, executive vice president
of the Beet Sugar Development Foundation of Denver, Colorado.
Schwartz says that this new guard brings the tools of
molecular biology to sugar beet breeding for the first timewithout
necessarily using genetic engineeringallowing a look at how a
sugar beet grows, down to the level of gene molecules. He cites McGrath,
in ARS's Sugar Beet and Bean Research Unit at East Lansing, Michigan;
Leonard W. Panella at Fort Collins, Colorado; and John Weiland at Fargo,
North Dakota, as examples of scientists ushering in an era of faster,
gene-based sugar beet breeding.
Technician Teresa Koppin
checks sucrose content of
a freshly harvested beet
using a near-infrared
Under a MOU (memorandum of understanding) with USDA, first
signed in the 1940s, the foundation provides germplasm, research assistance,
and funding for these and a handful of other ARS geneticists from Maryland
to California who are mapping the sugar beet genome. The group is one
of just a few in the world working on the sugar beet genome and the
only public breeding group in the United States doing so. ARS shares
all its data publicly.
Though half of America's sweet tooth cravingsand
a third of the world'sare satisfied by beet sugar, Schwartz says
the industry is still considered a small onea minor specialty
crop. There are only five small sugar beet breeding companies in the
world, all overseas, and the foundation represents all but one of them.
Geneticist Mitch McGrath
examines sugar beet plants
grown for rapid seed
production and accelerated
breeding of recombinant
USDA's Long-Term Agreement With Industry
The foundation acts as a research arm and umbrella organization
for its member companies. The MOU that's evolved over the years charges
ARS with developing basic germplasm lines and releasing them to the
foundation, which distributes them to members.
"Our companies are best suited for commercial development,"
Schwartz says. "They're not suited for the type of genetic program
McGrath and his colleagues around the country are working on. That's
very specific, and expensive, research." It recently yielded about
20,000 sugar beet gene indicator tagsESTs (expressed sequence
tags)which represent some, but not all, of the 30,000 genes thought
to make up the functional part of the genome.
The latest project funded under the MOU calls for screening
the sugar beet genome with another new tool, a BAC (bacterial artificial
chromosome) library. McGrath explains that a BAC library uses safe strains
of Escherichia coli bacteria to store sugar beet DNA. These sequences
are then either screened with genetic markers or compared with sequences
of known genes to connect them with possible traits. The same thing
is done with ESTs.
Shallow grooves of an
SR96 smooth-root sugar
beet (left) and a traditional
sugar beet. The smoother
roots don't harbor as much
soil when harvested and can
cut soil disposal costs
McGrath began with sugar beet DNA he prepared with Weiland
and worked with a contract firm to prepare and package the library.
Each clone in the library of 38,400 cloned bacteria stores a different
DNA sequence from the beet's genome.
"We chop up sugar beet DNA and connect segments to
bacterial plasmids that carry the DNA into E. coli bacteria,"
McGrath says. Schwartz explains that member seed companies can then
either buy cloned copies of the living bacterial library or DNA samples
on filters, as two have already done, or they can rely on McGrath or
the contract firm to compare their germplasm's DNA sequences with those
in the library to identify traitsor at least chromosome locationassociated
with each DNA sequence.
"This is an important first step to create order
in these early days of sugar beet genome mapping," says McGrath.
"We don't have a common language for any of the beet's nine chromosomes."
Michigan State University
plant breeding and genetics
graduate student Daniele
Trebbi prepares a sugar beet
for sucrose measurement in
But Will It Sprout?
Schwartz says that seedling emergence is one of the most
important traits to sugar beet growers everywhere. At an industry meeting
in 1996, Schwartz saw McGrath bombarded with requests for help on emergence.
As one grower put it, "If we don't get it out of the ground, it's
no good to us."
"McGrath put his nose to the grindstone," Schwartz
says, "and quickly came back with a simple test for the emergence
trait, which he gave to the foundation, and two possible genetic markers
for seedling emergence and vigor. His test for emergence has already
led to commercial varieties with higher germination rates." He
developed it by growing seeds in pure watercomparable to the multiple
stresses seeds encounter in the field.
His possible genetic markers promise to help identify
and locate the emergence genes on the chromosomes, one of the goals
of the genome project.
Paul Pfenninger, vice president of agriculture for the
Monitor Sugar Company in Bay City, Michigan, agrees that farmers' greatest
concerns are that the seed sprout and that the seedling survive its
first monthwhat's called "seedling vigor."
Technicians Tim Duckert,
Teresa Koppin, and Robert
Sims (left to right) harvest
sugar beets and test sucrose
content simultaneously. Koppin
is performing the sucrose
| "One unique thing about
sugar beets is that only about half of the seeds actually sprout,"
says Pfenninger. "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."
But disease remains the main threat. Farmers rotate their
beets with other cropsmainly corn, soybeans, and wheatto
avoid the disease buildup that can occur from growing beets in the same
field 2 years in a row.
McGrath's team consists of two technicians and three graduate
students. One student developed a test for Aphanomyces seedling
disease and used it to show there are two genes needed for resistance.
Another student is examining sugar beet germplasm to develop ideas that
could help in breeding for resistance to Rhizoctonia seedling
disease. The third has found that sugar beets radically alter expression
of a host of genes at about the same time that Rhizoctonia resistance
begins in fields.
Geneticist Mitch McGrath
pulls beets by hand to
check growth, root
conformation, and disease
resistance. Note the large
amount of soil that clings
to the beet.
| How Sweet Can It Be?
Pfenninger says that after emergence and survival, the
main concerns are yield and sugar levels. McGrath has found a possible
marker to predict beets with high sugar content when they're about 7
weeks old, instead of waiting for full growth in about 25 weeks. He
and colleagues theorize that beets with the highest sugar content aren't
better at storing sugar; they are just better at keeping the sugar concentration
high because they let less water in. McGrath and others had observed
that beets with the most sugar tended to be smaller and less watery.
Having worked for Monitor since 1978, Pfenninger understands
the value of having people like McGrath's team on his sidescientists
on the cutting edge of technology but still accessible and connected
to the real world of sugar beet growing, processing, and marketing.
Pfenninger has watched almost every other private beet sugar processing
company collapse, sold to farmers who organized co-ops to save their
local markets. A recent string of 30-year-low prices sped up the process.
How Smoothand HealthyCan It Be?
Another major industry concern is the tendency of mud
and soil to stick to sugar beets at harvest, embedded in natural ridges.
While processing shakes loose as much dirt as possible before weighing,
growers must truck it back to their farms. This not only burns diesel
fuel, but can also spread disease as soil is moved from field to field.
Dirt removed later in processing costs the industry a
lot of money. Monitor spends from one-half to three-quarters of a million
dollars each year disposing of the soil in special storage ponds and
dredging the ponds when they become too full.
Monitor worked with McGrath's team to develop new sugar
beet germplasm with smooth roots that will cut soil lossand disposal
costsby about half. They're now incorporating resistance to Rhizoctonia
and other diseases into this new germplasm. Working with Bob Lewellen,
an ARS geneticist in Salinas, California, they've 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
That germplasmdone without molecular genetic toolsis
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 pulling genes for desired traits off the "library
shelf" one gene at a time and combining the genes, using traditional
plant breeding, into new lines. Those lines will be the eventual payoff
of the genetic revolution. In the meantime, McGrath and colleagues will
continue to release ever better germplasmand better tools for
Comis, Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect
Genetic Resources, Genomics, and Genetic Improvement, an ARS National
Program (#301) described on the World Wide Web at www.nps.ars.usda.gov.
J. Mitchell McGrath
is in the USDA-ARS Sugar
Beet and Bean Research Unit, 494 PSSB, Michigan State University,
East Lansing, MI 48824-1325; phone (517) 353-9262, fax (517) 337-6782.
"New Breed of Beet Geneticists Shows How Sweet It Can Be"
was published in the April
2004 issue of Agricultural Research magazine.