Lubbock, Texas
May 19, 2005
A collaborative corn breeding project under way
at the Texas A&M University
System Agricultural Research and Extension Center at Lubbock is
paving the way for hardy, stress-resistant corns that yield well
under demanding growing conditions.
"We are making good progress in breeding less thirsty,
drought-resistant food and field corns that can resist heat,
insects and aflatoxin," said Wenwei Xu, Texas Agricultural
Experiment Station corn breeder, who holds a joint appointment
with Texas Tech University. "Corn lines bred to survive and
thrive in West Texas can be useful in other parts of the world."
The project employs the expertise of plant breeders,
geneticists, entomologists, plant pathologists, soil
specialists, irrigation engineers, plant ecologists and
Extension agents who represent two universities and USDA's
Agricultural Research Service in three states.
The scientists grow corn breeding lines and populations under
well-defined soil moisture conditions by controlling irrigation
and making selections based on a series of positive
characteristics.
"We know that under drought conditions, drought-tolerant plants
employ several mechanisms – such as strong root systems and
hydraulic lift," Xu said. "Some of our work centers on
transferring the genes responsible for these traits from
tropical germplasm into temperate corn lines bred to perform and
yield well under West Texas' sometimes harsh growing
conditions."
West Texas is a hot and dry environment. Even with irrigation
supplementing rainfall, crops are subject to drought stress. In
their field evaluations, the researchers noticed that some corns
were able to cope with this stress while others simply couldn't.
"We think this is due to a phenomenon known as hydraulic lift.
Some plants are able to lift moisture from their deep roots up
to the shallow roots just under the soil surface, and release
the moisture into the soil," Xu said.
"Corn roots can penetrate to a depth of several feet. But 80 percent of
their roots are concentrated in the top foot of soil. Plants
that can lift moisture from their deep roots to their shallow
roots at night can better withstand drought conditions."
This lifted moisture keeps the shallow roots functioning, which
improves the plant's ability to absorb crucial soil nutrients.
The researchers found that the most drought tolerant hybrids had
the greatest hydraulic lift capacity, and produced more grain
under moisture stress because their better root systems allowed
the plants to recover quickly once drought stress was relieved.
The researchers are also seeking corns that can resist insect
pests and plant disease – another part of the multiple-stress
resistance package.
"We are also selecting for resistance to corn earworms, spider
mites, and aflatoxin," Xu said. "Our hybrids have significantly
less aflatoxin compared to commercial hybrids, and similar
yield. Aflatoxin contamination degrades grain quality and market
price, and determines whether the grain can be sold as food or
livestock feed."
The process of transferring superior genes from tropical
germplasm into existing temperate corn lines is called
"introgression." It isn't easy work.
Crossing tropical and temperate corn germplasm requires hand
pollination in the field and greenhouse. Fortunately,
greenhouses and nurseries in Texas and Hawaii enable the
researchers to produce two generations of corn lines each year.
Crosses of tropical and temperate corn, and their offspring, are
then evaluated for multiple stress resistance in field trials at
more than 10 locations across Texas. Only the best of these
plants are selected as breeding candidates.
"Investigating the physiological and genetic mechanisms of
corn's stress resistance can be pretty slow work," Xu said. "To
speed it up, we use molecular marker-assisted selection in the
breeding process. By using molecular mapping and molecular
markers, we can do a better job of identifying and introducing
genes that impart positive traits."
This collaboration and hard work resulted in the release of
inbred corn lines in 2003 and 2004. These lines – Tx202, Tx203,
Tx204, Tx205 – have unique characteristics such as drought and
heat tolerance, earworm resistance and high yields.
The project has also produced advanced breeding lines and
experimental hybrids that are highly resistant to earworms and
yield as well as commercial hybrids. Better insect resistance
enables producers to use fewer pesticides and may open the door
for production of value-added, organic corn.
The research is funded by the Texas Corn Producers Board, the
High Plains Underground Water Conservation District No. 1, the
Texas Water Development Board, the Texas Department of
Agriculture's Integrated Pest Management program, and industry.
Some of the work is funded by the United States Department of
Agriculture-Agricultural Research Service pre-harvest control of
aflatoxin program and the Germplasm Enhancement of Maize (GEM)
project.
GEM is a cooperative effort of USDA's Agricultural Research
Service, land-grant universities and ag industry. It allows
scientists to share access to new public and private corn
germplasms.
"By diversifying the pool of corn germplasm available to public
and private breeders, we can accelerate the process of
developing productive, early-season corn hybrids with multiple
stress resistance," Xu concluded. "This could lead to hardier,
higher-value commercial corns for producers and the food and
feed industries. |