Forum21st-Century Sugar Beet Breeding
A sugar beet can be likened to a factory. To uncover the blueprint
for the factory, ARS started a
sugar beet genome project 5 years ago. You could say that proteinscoded
by genesare the workers. By understanding the proteinsthrough
unraveling the codes for the library of genes that produce themwe
will one day learn what the sugar beet factory has to do to make a beet
that is profitable to both farmers and industry.
The sugar beet genome consists of the complete set of chromosomes that
are in the nucleus of every cell of a sugar beet. Genomics, the relatively
new science of genome analysis, uses the latest genetic methods to extend
traditional breeding. But it does not require use of genetic engineering.
Genomics makes it possible to breed plants that possess a desired combination
of genes selected from the entire sugar beet genome.
As the story
on page 4 shows, we at ARSwith substantial funding from the
Beet Sugar Development Foundationhave begun a revolution in the
United States that will change sugar beet breeding from traditional
trait-based to gene-based selection. This means that farmers and the
rest of the industry will be able to order custom sugar beet varieties
selected for the genes they contain. An understanding of the genes and
proteins will make breeding faster than ever, because we will be able
to predict outcomes of crosses and choose the most efficient routes
to achieve desired ends.
All this means that better sugar beet varieties are on the wayand
To unravel the code the sugar beet blueprint is written in, we need
what Mitch McGratha geneticist at the ARS Sugar Beet and Bean
Research Unit at East Lansing, Michigancalls an "alphabet
soup" of genetic tools, such as ESTs (expressed sequence tags),
BACs (bacterial artificial chromosomes), and RILs (recombinant inbred
lines). We have to build these tools for sugar beets because very few
members of its plant family have been mapped.
Though we are in our first decade of this revolution, there are already
more than 20,000 ESTs; 5,000 RILs are on the way; and a BAC library
is in hand that covers the sugar beet genome 5 times over.
The East Lansing group and two independent groups in Germany deposited
the ESTs into the National Center for Biotechnology Information's GenBank
The sequence tags identify probably one-third to one-half of the 30,000
genes thought to make up the operational blueprint for the sugar beet
The RILs are specially bred to breed true, allowing us to separate
the effects of genes from the effects of disease, drought, or other
environmental factors. The BAC library has been built in collaboration
with ARS scientists at Fargo, North Dakota; Fort Collins, Colorado;
and Salinas, California.
These tools have helped McGrath and his team develop possible genetic
markers for the genes that control the proteins that enable sugar beet
seeds to sprout and the seedlings to survive the critical month when
they're at their weakest stage. This is the top concern of farmers.
McGrath has also found a possible marker for high sugar levels in beets.
Along with yield, sugar content is the second major area of concern
to farmers and the industry. And McGrath's team is on the trail of the
genes for resistance to two major seedling disease agents: Aphanomyces
and Rhizoctonia. Disease is the main threat to a seedling's survival
its first month.
The way genetics is advancing today, undoubtedly by the next decade
we'll be working with tools that don't exist today, adding still more
to this highly productive mix of technologies.
The BAC library is the first step toward creating order in these early days of sugar beet genome mapping. We don't even have a common language for any of the sugar beet's nine chromosomes. But we at ARS work very closely with university and industry scientists around the world to build advanced tools.
Thanks to ESTs, BACs, and RILs, we are already gaining insights into
solving problems once thought to be unsolvable. And progress is likely
to accelerate as these investments in genomics are leveraged with scientific
expertise from inside and outside the sugar beet community.
Just as the work of genetic researchers mapping the genomes of other
plants, such as rice, has given us a head start on sugar beet mapping,
we expect that our work will be useful to future efforts.
Genomics has made it possible to use the same basic tools to decode the blueprint for plant factories that make widely different products. Lessons learned in building genetic deciphering tools for one crop can save a lot of time and money in building them for others.
J. Scott Cameron
"Forum" was published in the April 2004 issue of Agricultural Research magazine.