Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Jones, Michael A

Committee Member

Greene , Jeremy K

Committee Member

Marshall , Michael W

Committee Member

Wells , Christina E

Abstract

Sweeney, Jason Allen. Glufosinate Tolerance of WideStrike¨ and LibertyLink¨ Cotton Varieties and the Recoverability of Cotton Following Terminal Removal. (Under the direction of Dr. Michael A. Jones).
To evaluate the effects of topical application of glufosinate (Liberty 280SL, 24.5% glufosinate-ammonium salt) on cotton varieties with WideStrike¨ and LibertyLink¨ technologies, two field experiments were conducted in 2011 and 2012 at the Pee Dee Research and Education Center (PDREC) in Florence, SC. In the first experiment, five WideStrike¨ cotton varieties (Phytogen [PHY] 367WRF, PHY 375WRF, PHY 440W, PHY 499WRF, and PHY 565WRF) and three LibertyLink¨ cotton varieties (FiberMax [FM] 1773LLB2, FM 1845LLB2, and Stoneville [ST] 4145LLB2) were sprayed topically with sequential applications of glufosinate at 0.59 kg haø_ (labeled rate) at the 1- to 3-leaf stage and the 7- to 9-leaf stage. Glufosinate- and weed-free plots were maintained as controls for each variety. WideStrike¨ varieties were up to 11% less tolerant to topical applications of glufosinate than LibertyLink¨ varieties. Symptoms of phytotoxicity, including leaf chlorosis and necrosis, appeared to be transient, and no differences in lint yield were found among the sprayed and unsprayed WideStrike¨ and LibertyLink¨ varieties evaluated at season's end. Regardless of gene expression for glufosinate tolerance, lint yield of cotton sprayed with glufosinate was 105 kg haø_ greater than that of unsprayed cotton and yield increases of sprayed cotton varieties are likely related to an increase in boll development. In the second experiment, PHY 375WRF and FM 1773LLB2 were sprayed topically at the 1- to 3-leaf stage, at the 7- to 9-leaf stage, and at both the 1- to 3- and 7- to 9-leaf stages with glufosinate at the 1, 2, 3, and 4x rates (0.59, 1.18, 1.77, and 2.36 kg haˉ_, respectively). In addition, each variety was sprayed topically at early bloom with glufosinate at the 1, 2, and 4x rates. Glufosinate- and weed-free plots were maintained as controls for both varieties. When glufosinate was applied at the 1- to 3-leaf stage, PHY 375WRF had 12, 21, 19, and 29% greater leaf injury than FM 1773LLB2 at the 1, 2, 3, and 4x rates, respectively. At the 7- to 9-leaf stage, PHY 375WRF exhibited 7, 11, 16, and 18% greater leaf injury than FM 1773LLB2 when glufosinate was applied at the 1, 2, 3, and 4x rates, respectively, and 9, 12, and 15% greater leaf injury than FM 1773LLB2 when glufosinate was applied at the 1, 2, and 4x rates early bloom, respectively. Application of labeled rates of glufosinate did not increase total leaf injury (percent leaf chlorosis + percent leaf necrosis) of sprayed FM 1773LLB2 compared with unsprayed FM 1773LLB2. At season's end, glufosinate application had no effect on total node accumulation or final plant height. Despite differing levels of glufosinate tolerance, no variety x glufosinate application interactions were observed for any plant growth, lint yield, or fiber property parameters evaluated. Compared with the untreated control, no differences in lint yield of sprayed cotton were observed. Glufosinate applied at the 3 and 4x rates at the 1- to 3-leaf stage reduced lint yield by 219 and 195 kg haˉ_ when compared with glufosinate applied at the 1x rate at the 1- to 3-leaf stage, respectively. Yield of cotton sprayed with glufosinate at the 3x rate at the 7- to 9-leaf stage was reduced 235 kg haˉ_ compared with cotton sprayed with glufosinate at the 1x rate at the 7- to 9-leaf stage.
A third experiment simulating crop injury due to biotic or abiotic factors was conducted at PDREC by evaluating the response of irrigated and dryland cotton following terminal removal at various growth stages. Terminals of PHY 499WRF were removed by hand at five distinct cotton growth stages and at eight different nodal locations. Using standard garden shears, mainstems were severed below the 2nd node at the 2-leaf stage, below the 2nd and 4th nodes and the 4-leaf stage, below the 4th, 6th, and 8th nodes at the 8-leaf stage, below the 8th, 10th, and 12th nodes at the 12-leaf stage, and below the 12th, 14th, and 16th nodes at the 16-leaf stage. An untreated control was also maintained in irrigated and dryland conditions. Irrigation had no effect on the ability of cotton to recover following terminal removal. Recoverability of cotton following terminal injury is dependent on growing conditions from season to season, whereas numerous year x TRT interactions were observed for plant growth and fiber quality parameters evaluated in this study. However, final lint yield of cotton following terminal removal does not appear to be dependent on growing season. Compared with the untreated control, lint yield of PHY 499WRF was reduced (from greatest to least) by 25% following terminal removal below the 8th node at the 12-leaf stage, 21% when terminals removed below the 12th node at the 16-leaf stage, 17% when terminals were removed below the 4th node at the 8-leaf stage, 16% when terminals were removed below the 10th node at the 12-leaf stage, and 11% when terminals were removed below the 2nd node at the 4-leaf stage. At a given growth stage, greater reductions in lint yield were observed when terminal removal treatments were applied at lower positions on the mainstem.

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