Cotton variety development a trade-off
Oct 2, 2002 12:00 PM, By Doreen Muzzi Farm Press Editorial Staff
Be careful what you wish for because you might just get it. That old adage rings true for many things, including cotton variety development.
Cotton breeders are able to breed improved fiber quality traits into new lines, but for the most part you trade yield for quality, says Bill Meredith, USDA cotton breeder with the Crop Genetics & Production Research Unit at Stoneville, Miss.
“Fiber quality is one of the easiest things to breed for, but we don't have a marketing system that encourages fiber quality,” he says. “There is a negative relationship between fiber quality and yield, and yield is the most rewarded trait in the cotton market.”
According to Meredith, who spoke at the recent meeting of Delta Council's Cotton Ginning and Quality Improvement Committee, for every hundredth of an inch in fiber length gained through breeding you lose about 12.1 pounds of yield per acre.
For example, on an average, if we increase length from 1.08 inches to 1.11 inches, we lose 36.3 pounds of lint per acre. “On average, if through breeding we increased strength by one HVI unit, we decrease lint yield 23 pounds per acre. That means if we increased strength from 27 to 29 grams per tex, we could expect to lose 46 pounds of lint per acre. If by breeding we reduced micronaire from 50 to 45, we would expect to lose 82.5 pounds of lint per acre,” he says. “These are the type of changes the textile industry wants made in U.S. cotton.”
These numbers illustrate the difficulty cotton breeders face working with more than one variety trait at the same time. “It's not worth it,” Meredith says. “We don't have a system that rewards high quality cotton, but without improved fiber traits we could ultimately lose markets. On the other hand, without high yield potential you may not even be in business next year.”
Meredith agrees there is room for improvement, with currently available cotton varieties in need of both a yield and quality boost. Backing up his belief are statistics showing that in 2001, 45 percent of cotton bales in Mississippi were discounted for micronaire, 20 percent were discounted for length, and 12 percent were discounted for fiber strength. The yield and quality traits exhibited by a cotton variety depend on genetics, the environment, and the interaction between the two.
Of these factors, the only one cotton breeders have the power to improve is the genetic component. “We have not improved yield one iota in the past 20 years. In fact, we're not even going in the right direction. We need a new cotton breeding strategy,” Meredith says.
In the past, he says, cotton breeding priorities were yield, earliness, pest resistance and fiber quality, in that order. Current breeding objectives focus on yield stability, fiber quality, pest resistance, added-value traits, and genetic management systems. The new world of transgenic breeding has, for the most part, focused on back-cross breeding methods using three genes.
While added-value has not added any yield or fiber quality in Meredith's view, he says it has simplified production management. “They are not without their problems, but their simplified management allows growers to farm a much greater acreage.”
Standing in the way of increased yield are problems with variety stability, emerging pest populations, changing management systems, and a narrow genetic base.
So why don't cotton breeders simply breed for improved fiber quality? In addition to its negative relationship with yield, current marketing systems are slow to encourage fiber quality, and there is no guarantee growers will be paid a premium for increased fiber quality. Can better cotton varieties be developed? The short answer, Meredith says, is yes. To do it, though, will take a new breeding strategy that promotes fiber quality and reinforces the entire cotton industry.
“If there is a dedicated effort to lower micronaire and hold yield levels it can be done, but it will take a concentrated effort,” he says.
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