DEVELOPING AND VALIDATING A MODEL FOR A PLANT-GROWTH REGULATOR

Mepiquat chloride (MC), 1,1-dimethylpiperidinium chloride, is a system ic plant growth regulator used extensively to regulate vegetative grow th in cotton (Gossypium hirsutum L. and G. barbadense L.). Yield respo nses to MC have been erratic, probably due to the difficulty in choosi ng the proper rate and timing of application. We developed a model bas ed on data collected by spraying various amounts of MC on 25-d-old pla nts. The effect of MC on various physiological parameters was measured . Stem elongation rate was reduced 38% due to 30 mu g g(-1) of MC, whi te leaf area expansion rate and photosynthesis was reduced 30%. The mo del adjusts the projected leaf expansion, stem elongation, and photosy nthetic 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 cot ton crop management. we tested the model against data for plant height s, mainstem nodes, and yields from several cropping systems across the U.S. Cotton Belt. The simulation results agreed closely with the obse rved 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 m odel. When used in association with GOSSYM-COMAX, the MC model may pro vide an effective tool for selecting precise timing and amounts of mep iquat chloride needed to optimize the proper use of the chemical.