Evaluation of transgenic cotton lines tolerant to glufosinate, bromoxynil, and both glufosinate and bromoxynil

The prospect of multi-transgene-stacking of herbicide tolerances provides opportunities for improved weed resistance management, enhanced weed control, increased flexibility, and decreased weed control costs.;Both bromoxynil-tolerant and glufosinate-tolerant cotton varieties have been previously developed. For the purposes of this study experimental cotton lines were developed that are tolerant to bromoxynil or glufosinate-ammonium and to both bromoxynil and glufosinate-ammonium. The lines were developed in order to evaluate the effects of the bxn and bar genes singularly and in combination on cotton growth, agronomic characteristics, and fiber properties.;Crosses were made between a bromoxynil-tolerant cotton line and plants from a glufosinate-ammonium-tolerant population. F2 derived lines were developed from each of these crosses that express either: (1) bromoxynil tolerance, (2) glufosinate-ammonium tolerance, (3) tolerance to both herbicides, or (4) no herbicide tolerance. Sixteen treatments (four crosses by four herbicide traits) were evaluated in a randomized block design with a factorial arrangement of treatments.;There were no significant main effect differences among herbicide traits in either the 2002 or 2003 tests, except for maturity in the 2003 experiment. Results from 2002 and 2003 experiments show significant interaction effects between cross and herbicide trait for storm resistance, plant height, and lint percentage, as well as the fiber properties of length, strength, micronaire, and uniformity; in addition, the 2003 results show a significant interaction for lint yield. The inconsistent differences observed over crosses among herbicide traits for each of the characteristics evaluated may be due to a relatively small effect from the expression of the herbicide tolerance genes when compared to the inherent variation typically observed in F2 derived cotton lines.;The variation observed in each of the characteristics evaluated, among the experimental lines, was within the normal range of what would be expected from non-transgenic cotton lines developed from F2 cotton populations. Thus, in these tests, the expression of the bar and bxn genes singularly and in combination did not substantially affect cotton growth, agronomic characteristics, or fiber properties.