William D. Caldwell, Hayes, James A., Hague, Steve, Myers, Gerald O. | 11/17/2004 1:08:14 AM
W. David Caldwell, Gerald O. Myers, Steve Hague and James A. Hayes
Systematic research in cotton breeding and genetic improvement began in Louisiana when H.B. Brown joined the staff of the Louisiana Agricultural Experiment Station (LAES) in 1926. The objectives of the cotton improvement and breeding program were to increase lint yield, to produce more uniform, longer cotton fiber and to produce larger bolls. Early studies by Brown also involved investigations of leaf shape and plant pubescence. In 1936, Brown was joined by John Cotton, a U.S. Department of Agriculture cotton breeder and geneticist who contributed to the improvement of disease resistance in LAES cotton germplasm.
When Brown retired in 1946, F.W. Self became the lead cotton breeder for LAES, and a major effort was initiated to improve fiber and seed quality. The release of Stardel in 1955 represented a significant advance in fiber strength and uniformity. Stardel Glandless was a commercial variety released in 1967; it was marketed as Rogers OB1.
M.T. Henderson served with Self and was involved in cotton genetics and taught many young scientists. Many of Henderson’s students went on to have a major impact on the cotton industry. One of these students, Jack E. Jones, was responsible for cotton breeding and variety development at the LAES from 1950 to 1990. Jones’ research focused on the Fusarium wilt-nematode disease complex, reniform nematodes, key insect pests (bollworm-budworm, boll weevils, plant bugs) and how open-canopy traits affected boll rot, earliness, insects and yield. These studies resulted in the release of three varieties with unique leaf shape: Gumbo, an okra leaf (narrow leaf) variety released in 1976; Pronto, a super okra leaf variety released in 1976; and Gumbo 500, an improved okra leaf variety released in 1981. From 1990 to 1994, Steve Calhoun conducted the cotton breeding and improvement program for the LAES. The present breeder, Gerald Myers, assumed responsibility for the program in 1994.
While there is little direct economic incentive for producers to sacrifice yield for fiber quality, cotton breeders, especially those in the public domain, are expected to be vanguards of cotton quality. Better fiber translates into better yarn, which enables cotton to compete effectively with synthetic fiber. Therefore, the health of the cotton industry depends on high-quality fiber.
Three of the most important traits for textile operations are fiber length, strength and fineness. Although length is primarily determined by the plant’s genetic makeup, stressful growing conditions can shorten fiber. Frequently, breeding lines with long fiber have low lint-to-seed ratios that can contribute to low yield. Fortunately, selection methods are being perfected to circumvent this conundrum.
Fiber strength is governed largely by genetics, with some loss attributed to severe weathering between boll opening and harvest, extreme plant stress during fiber development or harsh ginning practices. Fiber strength usually translates directly into yarn strength. This has become increasingly important in modern textile mills because machinery operates at escalating speeds with little economic cushion for work stoppages caused by breaks in the spinning and weaving processes.
Micronaire is an indicator of both fineness and maturity. Coarse fiber results in a lower fiber per thread count and a low quality fabric. Immature fibers cause more fabric imperfections and are difficult to dye. In Louisiana, most immature fiber is produced in the uppermost fruiting sites, which are often lost to late-season insect pests or not harvested by once-over picking practices. Since the bulk of Louisiana cotton develops in systems promoting fiber maturity, micronaire becomes primarily a measure of fineness. Fiber fineness is almost under complete genetic control, with environment having little effect. Unfortunately, concessions occur between development of low micronaire and high yield. With other factors being equal, an increase in micronaire results in more pounds of lint per acre.
With cooperation of researchers from several disciplines and support from producer organizations, great strides have been made in improving fiber quality and enhancing yield. Researchers at the Pee Dee Experiment Station in South Carolina were some of the first to improve yield and fiber traits simultaneously. The Texas A&M cotton breeding program at Lubbock, with support from Plains Cotton Growers, Inc., is releasing upland cotton germplasm with 35 percent better fiber length and 50 percent better strength than regional standards, with little to no trade-off in yield potential.
An important aspect of the cotton improvement effort has been the Cotton Fiber Testing Laboratory located on the LSU campus in Baton Rouge. The fiber lab, operated for many years by Wilbur Aguillard and more recently by Ivan Dickson, was recently equipped with a modern Uster High Volume Instrument for comprehensive fiber evaluation. This service is invaluable in providing information on the fiber quality.
Principal genetic resources that enhance fiber traits are from Acala breeding lines and naturally occurring variation within adapted varieties. Acala lines are primarily grown in the western United States and Australia but have been moderately successful in Louisiana. Most cotton producers remember Deltapine 90, which had an Acala background. More recently, several lines from Australia have been commercially introduced with extensive genetic contributions from Acala lines. Cotton varieties are not entirely homogeneous populations and possess variation for most traits. Unfortunately, finding these traits can be likened to the proverbial needle in the haystack. Breeders may closely examine tens of thousands of plants before finding a single off-type improvement.
Cotton Breeding Program
The Cotton Breeding and Genetics Program of the LSU AgCenter seeks to build on its successes, which were significant in the 1990s. These include the release of several cotton varieties developed by Jack Jones—Stoneville LA 887, Paymaster (Hartz) 1215, 1220, 1244 and 1560. Transgenic versions of these varieties have also been marketed. Notable among these is Paymaster 1218BG, the most widely planted cotton variety in the Mid-South for two consecutive years in a row (2001 and 2002) and Stoneville ST 5599 BR (a transgenic version of LA 887), marketed for the first time in 2003. Both have the Bollgard gene for insect resistance and the Roundup Ready gene for herbicide resistance. Royalties from the sale of seed support the LSU AgCenter breeding program and other related research. Additional research was conducted into natural plant traits that confer resistance to insect pests and stresses, the identification of resistance to nematodes and the genetic inheritance of numerous traits. Germplasm from this research was developed and released for use by other cotton breeders.
Since 1994, the Cotton Breeding and Genetics Program has been directed by Gerald Myers and retains the historical focus of developing cotton germplasm and varieties with high yield potential, increased resistance to pests and superior fiber quality specifically adapted to Louisiana and the Mid-South. Research trials are undertaken in collaboration with LSU AgCenter scientists and research stations throughout the state, as well as cotton breeders across the United States.
The breeding program is based on a pedigree system. Recent focus areas beyond that of high and stable yield and superior fiber quality include developing germplasm with tolerance to both root-knot and reniform nematodes (highly destructive soil pests of cotton widely scattered in the state), developing germplasm with resistance to Heliothis pests and developing varieties with the okra leaf shape.
Research projects recently concluded have shown that the insertion
of transgenes for insect and herbicide resistance has made subtle changes in other plant characteristics and has identified new sources of resistance to the root-knot nematode. With recent grants from Cotton Incorporated and the Louisiana Cotton State Support Committee, research projects on improving the efficiency of breeding for better yield and fiber quality and on characterizing newly acquired cotton germplasm from Uzbekistan have begun.
Beginning in 1995, the program has been conducting research in cotton molecular genetics and biotechnology. Support from the Louisiana Educational Quality Support Fund helped establish this aspect of the program, which has two focus areas: molecular mapping of genes for yield components and fiber quality and on cotton transformation. A recent paper reports on the identification of a marker associated with increased yield in cotton. This DNA marker is being further investigated for its use in marker-assisted selection of increasing cotton yield. Efforts to develop the capability to genetically transform cotton are under way. Regenerated plants have been developed and research to increase the efficiency of the process is being conducted. This research is complementary to the conventional breeding program, and it is through a combination of the two that progress by the Cotton Breeding and Genetics Program can be measured.