Chlorophyll a Fluorescence Parameters do not Detect Yield-limiting Injury from Sub-lethal Rates of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Cotton (Gossypium hirsutum)
Seth A. Byrd *
Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK, USA.
John L. Snider
Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
Timothy L. Grey
Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
A. Stanley Culpepper
Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
Jared R. Whitaker
Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
Phillip M. Roberts
Department of Entomology, University of Georgia, Tifton, GA, USA.
Daryl R. Chastain
Department of Plant and Soil Sciences, Mississippi State University, Stoneville, MS, USA.
Wesley M. Porter
Department of Crop and Soil Sciences, University of Georgia, Tifton, GA, USA.
Guy D. Collins
Department of Crop and Soil Sciences, North Carolina State University, Rocky Mount, NC, USA.
*Author to whom correspondence should be addressed.
Abstract
Aims: Determine if the use of novel chlorophyll a fluorescence parameters could be utilized to predict yield loss of cotton exposed to sublethal rates of 2,4-dichlorophenoxyacetic acid (2,4-D) at various growth stages.
Study Design: All trials were arranged in a randomized complete block design with four replications. Treatment means were subjected to analysis of variance and linear regression was utilized to determine relationship between chlorophyll a parameters and yield.
Place and Duration of Study: University of Georgia Gibbs Farm in Tifton, GA, USA and the Sunbelt Agricultural Exposition in Moultrie, GA, USA during the 2013 growing season.
Methodology: Two sublethal rates of 2,4-D were applied to cotton at six distinct growth stages. The rates consisted of 2 g and 40 g ae ha-1 equivalent to 1/421 and 1/21 of the full rate (0.532 kg ae ha-1), respectively. The sublethal rates were applied to cotton at six growth stages, including the four leaf, nine leaf, first bloom, two, four and six weeks after first bloom growth stages. A fluorometer was used to obtain the fluorescence parameters Fv/Fm, ΦEO and PIABS from the uppermost fully expanded leaves at various intervals after 2,4-D exposure.
Results: Despite yield losses ranging from 20 – 90% of the non-treated control, no consistent patterns resulted from utilizing fluorescence transients to detect 2,4-D injury and overall instances of significant difference were minimal and typically not biologically relevant. In many cases, treatments exposed to 2,4-D that exhibited yield loss showed evidence of greater photosynthetic efficiency than the non-treated control. In the majority of instances, many of fluorescence parameters measured fell within ranges observed in previous studies in cotton produced under typical or non-stressed conditions.
Conclusion: While it has been proven as a valuable tool in other plant screening endeavors, chlorophyll a fluorescence were not able to detect the effects of sub-lethal rates of 2,4-D on cotton, even in instances that resulted in severe yield loss.
Keywords: FvFm, ΦPSII, photosynthetic performance index, OJIP.