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Genetic key to cottonseed, oil problems

Cotton seed size, gossypol content, and seed coat fragments — all problems for the cotton industry — are highly variable, heritable traits that can be solved through breeding.

But, says Ed King, there is a very important trade-off: lint yield. “We can select for each of these in the breeding process,” he said at the joint meeting of the Delta Council’s Ginning and Cotton Quality Improvement Committee and the Southern Cotton Ginners Association at Stoneville, Miss., “but we run the risk of sacrificing yield. And since lint yield drives the market, it is the primary goal of breeders.”

Gossypol, a chemical within the cotton seed, has been a drawback to feeding cottonseed and cottonseed meal to ruminant animals because of its toxicity.

King, who is director of the Mid-South region of USDA’s Agricultural Research Service, says ARS scientists have identified two optical forms of gossypol, a plus isomer and a minus isomer, and the technology to separate them out.

The minus isomer is more toxic to ruminant animals.

“This kind of research has been going on for years,” he says, “but now our geneticists are looking at it at the molecular level to develop low minus isomer cotton germplasm lines.”

In another study, researchers have shown that field moisture is an influence on both gossypol and fatty acid content, and that levels of both rose as field moisture increased.

They have also found that natural gossypol can be converted, through oxidation, into gossypolone, which has shown promise in inhibiting the growth of cancer cells. That research is ongoing, primarily at the ARS Southern Regional Research Center at New Orleans.

Increased consumer demand for food products with low or zero trans-fatty acids has focused additional attention on cottonseed oil. Frito-Lay, in the past couple of years, has switched much of its snack food processing from cottonseed oil to sunflowerseed oil.

“Partial hydrogenation of cottonseed oil to prevent rancidity produces these undesirable trans-fatty acids,” King notes. “We’ve found that fatty acid content is a quite heritable trait that is affected by cotton variety and location.

“The national cotton variety trial is being expanded to include wild cotton species in an attempt to expand the genetic base and open the path to developing cotton lines low in fatty acid content.

“But we have to acknowledge that lint yield is the primary driver for the cotton crop, not the seed or oil — although both enhance the overall profitability.”

Other cooperative research is being conducted to look at hydrogenation, blend, and interesterification of cottonseed oil to reduce trans-fat levels, and on the use of cottonseed oil as biodiesel, fuel additives, or lubricants.

Seed coat fragments in cotton lint, an ongoing problem for the industry, cause an increase in neps and white specks that reduce lint quality and affect cloth dyeing and unevenness.

“We’re looking at ways to reduce this,” King says, noting that seed coat fragmentation starts in the field and is exacerbated in the ginning process.

Small seed an immature seed are more likely to be damaged or pulled past the ginning point with the lint.

“A beltwide study of commercial gins is now under way to assess seed coat fragments associated with tinning, and modifications to gin machinery and harvesters are being assessed here at our Stoneville ginning lab.”

Seed coat fragment content has also been shown to be variable and heritable, King says, which means it can be reduced through breeding.

“Other technology is being developed at the New Orleans center on techniques for rapidly scanning the cotton surface to measure seed coat fragment content, as distinguished from other trash such as leaf and bark, and the neps level in fabric.”

King said the New Orleans facility is now fully functional following damage due to Hurricane Katrina. “There was quite a bit of damage to laboratory equipment, but much of it was obsolete anyway.”

A $35 million appropriation from Congress “has allowed us to get some very modern equipment that lets us refocus our research in some high priority areas, including cottonseed oil.”


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