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Developing and Validating a Model for a Plant Growth Regulator

Dep. of Plant and Soil Sciences, Mississippi State Univ., Mississippi State, MS 39762

A. R. Reddy and Harry F. Hodges^*

Life Sci. Dep., Pondicherry Univ., Pondicherry 605014, India
Dep. of Plant and Soil Sciences, Mississippi State Univ., Mississippi State, MS 39762

Sammy B. Turner and James M. McKinion

USDA-ARS, Mississippi State, MS 39762

^* Corresponding author.

Mepiquat chloride (MC), 1,l-dimethylpiperidinium chloride, is a systemic plant growth regulator used extensively to regulate vegetative growth in cotton (Gossypium hirsutum L. and G. burbadense L.). Yield responses to MC have been erratic, probably due to the difficulty in choosing the proper rate and timing of application. We developed a model based on data collected by spraying various amounts of MC on 25-d-old plants. The effect of MC on various physiological parameters was measured. Stem elongation rate was reduced 38% due to 30 µg g^–1 of MC, while leaf area expansion rate and photosynthesis was reduced 30%. The model adjusts the projected leaf expansion, stem elongation, and photosynthetic rates based on the crop growth status and concentrations of MC in the tissues. The MC subroutine was incorporated into GOSSYM-COMAX, a combined simulation model for plant growth and decision aid for cotton crop management. We tested the model against data for plant heights, mainstem nodes, and yields from several cropping systems across the U.S. Cotton Belt. The simulation results agreed closely with the observed field data. The new model reduced the overall variability 32% for predicting plant heights, 4% for predicting number of mainstem nodes, and 17% for predicting lint yields over the previously published MC model. When used in association with GOSSYM-COMAX, the MC model may provide an effective tool for selecting precise timing and amounts of mepiquat chloride needed to optimize the proper use of the chemical.

Received for publication April 4, 1994.

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