MODELING THE DOSE RESPONSE OF POINSETTIA TO A CHLORMEQUAT GROWTH RETARDANT APPLICATION

The dose response to a single foliar application of the growth retardant chlormequat for poinsettia (Euphorbia pulcherrima Klotz.) was quantified. The dose response function assumed that the initial retarding effect was independent of concentration between 500 and 4000 ppm and that concentration primarily affected the duration of growth-retarding activity. The dose response function was incorporated into a phasic mathematical function of stem elongation of single-stem (i.e. unpinched) poinsettia plants. The model was calibrated using a data set from plants receiving foliar sprays at a wide range of chlormequat concentrations. The resulting R² was 0.99, and the model also closely fit the dose response pattern for plants grown in an independent validation experiment. Additional information about growth retardant physiology would be needed to develop a more mechanistic dose response function.