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.