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.