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Fiber quality issue complex, scientific discussion needed

FIBER QUALITY. If there has been a buzz phrase recently in the industry, it is “fiber quality.” Everyone has an opinion on the causes of quality problems, but the industry is pushing to move from discussions based on anecdotal evidence to scientific evaluations.

Andy Jordan, director of technical services for the National Cotton Council, is one strong supporter of the industry entering a problem-solving mode. “We have certainly seen some issues with fiber quality in the past few seasons. And while we would all like to find a simple solution, the reality is fiber quality is a highly complex issue. There is not a single factor that we can point to as the culprit.”

Early on this season, most of the Cotton Belt had been experiencing good environmental conditions, the kind that favors good quality lint. However, late season rains are now threatening the crop in some areas, in some other areas quality has already been significantly impacted. The environmental component is an area in which a good deal of research has been conducted.

“Beltwide research has demonstrated the effect of environment on fiber quality. In 110 tests across the country where seven varieties were grown over a two-year period, we combined the effects of weather as well as management factors together as ‘environment,’” says Tom Kerby, Vice President of Technical Services at Delta and Pine Land Company.

“In these tests, environment proved to be far more important than differences in genetics or variety for growth and development factors. We then carried the analysis of environment and variety further using both company and public Official Variety Test (OVT) data comparing 16 varieties over three years and reported results for yield, fiber quality and growth parameters. On the average, the total variation (environment, variety or the interaction) was attributed to environment for fiber length in 85 percent of the instances and micronaire 68 percent,” he adds.

The advent of many new varieties on the market and difficulty in comparing qualities over time has led some to believe that fiber quality has been neglected in varietal development. On the contrary, Kerby states that fiber quality is at the forefront of D&PL's breeding program and has been for decades. Kerby explains that growers are going to plant the varieties that make them the most money.

“Farmers are going to plant what gives them the greatest economic returns, and payment for the crop places the greatest value on lint yield, not quality. That leads farmers to rightly place the greatest emphasis on yield when choosing varieties for their operation. Because of some of the impact the late season has traditionally had, we also see a push on the farm for earlier maturing varieties, which do not get the benefit of the longer season's photosynthate supply. So, in many places, farmers have selected the variety that produces the most lint within their management scheme, and looked at quality characteristics much later in the process. But we are currently introducing varieties that will improve both yield and quality,” he says.

Depending on the environment in which a crop develops, any variety can, under adverse conditions, be restricted in fiber length. According to Kerby, most fiber development takes place over roughly a 40 to 45-day period during boll development. The first 21 days are mostly fiber elongation, which determines fiber length. The last half of the boll development phase is to add cellulose to the fiber in daily rings on the inside of the fiber.

“The environmental effects on length and micronaire are tremendous. However, we should see better quality from most of the Cotton Belt this year, except for South Texas, which again suffered from drought. Of course, different quality issues are beginning to present themselves in the Delta ranging from spotting to discoloration from seed sprouting in the boll,” he adds.

“During the past three years many areas in the Cotton Belt have suffered prolonged drought sometimes accompanied by elevated temperatures. This has affected both productivity and quality. The result has been a tendency to question the yield performance, the fiber quality and the yield and fiber quality stability of the new varieties being produced,” he adds.

Kerby explains that water stress during early bloom can result in shorter fiber length. Water stress significant enough to reduce fiber length during the elongation phase would also typically reduce yields by reducing the number of fruiting sites on the plant or the size of the bolls. A related factor, high temperature, can also reduce fiber length by causing earlier termination of fiber elongation. Varieties that fruit rapidly may encounter a short period of water stress that impacts a larger portion of their final boll load. Comparing this to full-maturity varieties that extend their bloom period where obviously a smaller portion of the overall boll load is in the elongation phase when a water stress occurs.

Environmental stress has a similar effect on micronaire. At approximately 17 days after flowering, fibers begin secondary thickening, and by 21 days thickening restricts further length development. At the same time, the fibers develop daily inner rings until they are mature. More inner ring development increases micronaire. Available carbohydrates and temperature influence the development of these inner rings, as fiber development is a very high carbohydrate priority.

Kerby also notes that environmental effects can create situations where fiber qualities differ within the same plant. “Variability of quality also exists within the plant for all different fiber qualities. Micronaire, which measures the fineness and the maturity of the fiber, is a good example,” says Kerby.

Micronaire varies within the plant because bolls mature under differing conditions and at different times. Fiber maturity is related to the carbohydrate supply available to the individual bolls.

Bolls produced at the first position, in the lower to middle fruiting branches develop during the time of maximum carbohydrate supply, and consequently have the highest micronaire of any bolls on a plant. Bolls that develop on second and third positions have lower micronaire because the leaves, which supply carbohydrate to the bolls, are frequently shaded. Micronaire is measured by airflow through a constant weight of compressed fibers.

While critics have questioned the role of biotechnology in the quality debate, data conclusively shows no correlation. Kerby says transgenic introductions have had little effect on the fiber quality of the U.S. cotton crop. “Results from detailed fiber and spinning tests conducted by the International Textile Center demonstrated transgenic versions of DP 5415 and DP 5690 were essentially the same as their conventional parent varieties.

“In 213 direct comparisons of conventional and Roundup Ready® varieties, staple length was 0.01 shorter for Roundup Ready varieties while fiber strength and micronaire were the same. In 179 direct comparisons of conventional parents to the stacked versions, fiber length and strength were equivalent, while micronaire was reduced for the stacked varieties,” he says.

Research consistently shows that when environmental conditions are adverse, fiber quality is likely to suffer. New D&PL varieties have the potential to improve the situation, but bringing new varieties to the marketplace with both high yielding and high quality traits is not easy.

Years of testing and development are involved and the seed companies must forecast the needs of the farmer and the industry several years in advance. D&PL's tests show that the new conventional and transgenic varieties it is bringing to the marketplace in 2002 and 2003 has great potential for both higher yields and higher quality. For the farmer and the industry, these new varieties are coming at the right time.

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