Liberty link® cotton: Tolerance and weed management systems

Due to the recent progress made in biotechnology, new herbicide resistant cultivars are now available to help control weeds in cotton. In 1995, joints projects by the USDA-ARS, Texas Agricultural Experiment Station, Texas Agricultural Extension Service, and Texas Tech University in Lubbock were developed to provide Texas producers with improved germplasm for herbicide, insect, and disease resistance, environmental stress tolerance, and value-added traits for fiber and seed. A Liberty Link® cotton line was produced by using a DNA fragment containing the coding sequence of the bar gene from Streptomyces hygroscopicus, which is responsible for coding the pat enzyme. The chimeric bar gene was introduced into Coker 312 using Agrobacterium infection. Infected plants were screened for tolerance, which is achieved by metabolism. In 1997 and 1998, field experiments with the new Liberty Link® cotton line were conducted at the Texas Agricultural Experiment Station near Lubbock. Cotton growth and development was evaluated following Liberty(TM) applications at various growth stages, at different rates, and with sequential applications. Weed management systems with Liberty Linka cotton also were evaluated. Liberty(TM) was first applied at 0.54 pounds ai/A to Liberty Link® cotton at the cotyledonary, 2-3 leaf, 4-5 leaf, first square, first bloom, peak bloom, cutout, or 50% open boll stages of growth. In a second test, LibertyO was applied to 2-3 leaf cotton at 0.36, 0.72, 1.44, and 2.88 pounds ai/A. In a third test, Liberty(TM) was applied to cotton in the 0-1, 3-4, 9-10, and 14-15 leaf stages in single and repeated applications. The treatments were applied using a tractor-mounted compressed air sprayer or CO₂ backpack sprayer that delivered 10 GPA. In 1997 test plots were 2 rows by 25' in length due to availability of seed, while in 1998 test plots were 4 rows by 40'. During both years, plots were maintained weed-free throughout the growing season. Visual injury was evaluated 7, 14, and 21 days after treatment. Plant heights were evaluated 21 and 56 days after treatment. At harvest plants were mapped and lint yield and fiber quality determined.