A MODEL OF CHRYSANTHEMUM STEM ELONGATION

The relative progression of lateral shoot elongation from pinch to flo wer of chrysanthemum [Dendranthema grandiflora (Ramat.) Kitamura 'Brig ht Golden Anne'] plants grown under 2 to 22 mol.day-1.m-2 photosynthet ic photon flux and 10 to 20C was modeled using Richards function. Para meters for the function were determined by first transforming data of shoot length and time from pinch (start of short photoperiods) to flow er to a relative scale of 0.0 to 1.0 by dividing all intermediate shoo t lengths and measurement dates by final shoot length and number of da ys to flower, respectively. Data used for parameter estimation origina ted with plants grown at a daily average of greater-than-or-equal-to 2 0C, since those grown at a daily average above 20C exhibited delayed m orphological flower induction and reached 50% of the final shoot lengt h earlier in development. Relative shoot elongation was described by R ichards function in the following form: Relative shoot length = S(F) x {1 + [(S(F)/S(O)))N -1] x e(-SFKt)}-1/N where t (relative time) = 0.0 to 1.0, S(F) (maximum relative shoot length) = 1.018, S(O)(relative s hoot length at t = o) = 0.0131, N (model parameter related to the shap e of the curve) = 0.3923, and K (model parameter related to mean relat ive growth rate) = 5,8138.