Top Crop Manager

Features Agronomy Plant Breeding
Use of dihaploid a boon to corn business

Process streamlines breeding.

November 14, 2007  By Top Crop Manager

18aSpeeding the process of selecting for new hybrids is viewed with skepticism
by some in the plant genetics and breeding business. The fear is that something
might be missed in the 'chase' for a new and improved corn hybrid.

By using dihaploid technology, however, the speed with which new hybrids are
developed does nothing to weaken the process, it actually strengthens it.

Dihaploid refers to a system that develops new corn parent lines in the process
of making haploid plants and then doubling the chromosomes. The plant breeder
induces the genetic population, so that it will form kernels that grow to be
haploid plants. The haploid plants have 10 chromosomes that come from the maternal
parent, which is the genetic population. Normal corn plants have 10 pairs of
chromosomes, one side of the pair from the maternal plant and the other from
the paternal side. In classical breeding, because the plants get genes from
both parents, which are contributing different genes, the plants can segregate
or change each subsequent generation. In the haploid plants, there are genes
from only the maternal parent.


Then with a chemical treatment, it causes the chromosomes to double, giving
10 pairs, just like a normal corn plant.

The advantage is in one step, there are identical genes on both chromosomes
of a pair, giving 100 percent genetic stability. "With the dihaploid process,
we still have the same opportunities to sample and select for all the genes
that exist in corn," explains Harry Brokish, director of product development
for AgReliant Genetics, near Champaign, Illinois. Pride Seed is a member company
of AgReliant.

Hybrid screening and selection for traits can be accomplished faster and easier
because the parents of the new hybrids are completely pure or homozygous, at
the first level of testing.

Yet, despite fears that speeding the breeding process will allow for something
to be missed, Brokish points out that the only real shortcut using dihaploid
is in the generational breeding or the F1 to F8 stages. "Those generations
normally take four years with two generations per year," he says. "But
we do this in one year and additionally, the final developed parent line is
more genetically stable than the traditional method of self-pollinating."

From that stage, the hybrids are put through performance trials, registration
and seed production stages, along with quality control checks. The hybrids from
AgReliant research are then marketed through their member companies.

Brokish adds that in the commercial breeding field, the rate of gain using
the dihaploid method will be higher than in classical breeding methods, simply
because the sheer number of cycles that can be conducted over a 10 year period
of time is significantly increased versus conventional. "We don't believe
we will miss something with this method, and it comes down to experience with
the technology in an applied breeding program," says Brokish. He adds it
takes a certain level of understanding of available germplasm and the testing
methods the breeder uses to ensure the probability of finding a successful new

Very secretive
Although the dihaploid process is relatively simple, the chemical formula that
is the most cost effective for the inducer is not, nor is it well-known. According
to Brokish, only four or five people in the world know its formula, much the
same as those who work for soft drink or fast food companies. But unlike inducers
employed by other seed companies, AgReliant's is non-toxic and safe to work
with and the excess could be applied to lawns. Their competitor's inducer requires
a toxic handling procedure and dump site for the excess.

"Some of the major seed companies use different techniques to produce
their dihaploid lines, but most have less experience with this breeding technique
because they started later or took longer to get their program established,"
says Brokish. The expertise on AgReliant's part has created greater efficiencies
and breeding for new hybrids. "There is a significant number of commercial
hybrids that have been developed through the use of this technology." -30-



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