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Salt in Topsoil Poses a Challenge for Plant Biologists

United Press International

Worldwide food shortages are being compounded as increasing salinity leaches out of irrigated soil and into the roots of crops, serving as a vivid reminder of how the salt of the earth can kill.

Plant biologists think that a practical and economical solution to the problem is outfitting several varieties of edible plants with powerful new genes for salt resistance.

Scientists see this as a far less costly way of dealing with the inevitable salt invasion of irrigated land, because flushing fields with treated, salt-free water can be prohibitively expensive.

If genetic-engineering progress continues at the current rate, corn, wheat, millet and other grains could be genetically overhauled by the beginning of the 21st Century, and made resistant to conditions that would have wiped out their ancestors.

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The trick to getting new genes in old plants is cracking the DNA codes of several unusual species that have dwelt for centuries in salt marshes and remote desert regions where only the heartiest plant ever dared take root.

Mindful that corn withers in saline soil and wheat fails to thrive, scientists are scouring the genetic apparatus of salt marsh grasses, plants in the beet family and other plants, hoping to find genes that can be adapted to crops.

The marsh grass tolerates salty soil because its cells have been genetically programmed over thousands of years to accommodate harsh chemical realities. Once the resistance genes are found, scientists can begin the arduous task of cloning these and other genes that may one day render crops resistant to a variety of root-killing compounds.

“We’re looking for proteins and nucleic acids which are stimulated and turned on in response to salt,” explained molecular biologist James Heyser of Los Alamos National Laboratory in New Mexico.

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Heyser and his team are on a search for the protein products of salt-resistant genes as well as the actual salt-resistant genes themselves.

“We’re trying to locate the genes and use techniques of recombinant DNA to adapt them to grains,” he said. “We want to transfer specific enzymes from tolerant species to sensitive species and demonstrate that it’s possible to make salt-sensitive species more tolerant.”

Farmland worldwide is becoming increasingly overloaded with salt as a direct consequence of irrigation. As the irrigation water evaporates and is absorbed by plants, the salts in the water are left behind in the soil. California’s fertile Central Valley--some of the most productive farmland in the nation--has been particularly affected by this salt buildup, Heyser said.

10% of Nation’s Crops

California produces 10% of the nation’s crops in terms of dollar value, state estimates indicate, but profits often are rolled over to combat salt buildup.

Irrigation agriculture has been a fact of farming life in California for about a century. It has caused a gradual but appreciable rise in the amount of salt in Central Valley land, Heyser said.

“Twenty-five percent to 33% of all farmland in the United States is having problems with salination and the problem is getting worse,” explained Heyser, citing federal estimates.

“In the Third World,” he said, “it’s the same story.”

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Heyser and his team hope to develop new strains of corn and other grains, “because 60% of the calories consumed by people come from starch.”


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