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Study Paves Way to Water-efficient Cotton
A six-year study by University of Georgia and Israeli scientists has paved the way to cotton varieties that can brave the weather's whims by using water more efficiently.

"The most immediate discovery is that, at least in principle, we can 'reassemble' in cultivated cottons the sets of genes that enable wild cottons to survive under semiarid conditions," said Andrew Paterson, the UGA professor of crop and soil sciences, botany and genetics who headed the study.

Genes Believed Lost

"Many of these genes were thought to have been lost in the process of domesticating cotton for high yields under well-watered conditions," said Paterson, who also directs the UGA Center for Applied Genetic Technologies.

Paterson worked with Yehoshua Saranga of Hebrew University and Daniel Yakir of the Weismann Institute in Israel. Together, they devised a way to locate the genes that make cotton plants use water efficiently.

Saranga identified varieties of two cotton species shown in 1993-95 tests to make the most of the water they get. They then crossbred the two cottons.

Exploiting Genetic Potential

"This strategy enabled us to better exploit the genetic potential for arid-land adaptation found in each of the respective species," Saranga said.

The scientists assessed the amount and quality of cotton the plants produced with and without ample water.

Finally, they used a complete molecular map of the cotton genome to locate the genes that contribute to the plants' productivity and fiber quality.

"In each of the two parents of the population we studied," Paterson said, "we found different genes that confer improved quality and/or productivity under water deficits. These can be 'reassembled' or 'pyramided' into a new genotype that is better than either parent."

Weather's Whims

The findings have huge implications for cotton growers.

"Without question, weather has more effect on cotton productivity than any other factor," said Steve Brown, a cotton scientist with the UGA College of Agricultural and Environmental Sciences. "Anything that would give the plant more staying power would be a big bonus."

Water-use efficiency isn't a simple trait that can be easily fixed by a genetic silver bullet. It's a much more complex trait, Paterson said, involving many quantitative trait loci, or QTLs.

Complex Traits

"QTLs are the locations in the genome of genes that collectively act to determine the hereditary basis of complex traits such as height, or propensity to cancer," he said.

"These traits are influenced by many genes, plus environmental factors," he said. "Most measures of agricultural quality and productivity are such complex traits. They're affected by many genes that act at different times throughout the plant's life cycle."

The recently completed study, funded by a U.S.-Israel Binational Agricultural Research and Development grant, used established cotton breeding lines. Paterson said wild cottons are likely to have many more genes for water-use efficiency.

More Studies Needed

"These haven't yet been studied," he said. "But they need to be. We continue to look for new funding sources to breed improved germ plasm containing the genes we've discovered and to search for additional valuable genes."

Building on the 40 or so genes already discovered, Paterson said a conservative goal for further research is to "increase water-use efficiency in elite breeding lines by 10 percent."

If Georgia cotton farmers could reduce their water use by that much, they'd save 12 billion gallons of water statewide.

500,000 Swimming Pools

To put that into perspective, the standard swimming pool holds about 25,000 gallons of water, said Kerry Harrison, a UGA Extension Service engineer. "So 12 billion gallons of water is enough to fill about 500,000 pools."

CAES economist Don Shurley said using that much less irrigation would save cotton growers $2 million a year.

Beyond water savings, though, the study found QTLs that contribute to cotton quality and productivity with limited water and with ample water.

"The combination of these regions into one genotype," Saranga said, "is expected to result in a better adaptation to a wide range of environmental conditions."

Balancing the benefits to farmers, too, are the water needs of an increasingly urban state. "Georgia must produce more cotton with less water," Paterson said.

(Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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