Modelling external quality of cut chrysanthemum: Achievements and limitations

This paper provides an overview of the achievements and limitations of modelling external quality of cut chrysanthemum. A series of greenhouse experiments were conducted in different seasons to quantify the effects of the climate conditions and of the cultivation practices. This information was used as the basis for parameter selection and estimation, and for building the modules for plant height, number of flowers per plant and individual flower size. Increased assimilate availability by higher daily incident photosynthetic active radiation (PAR, 4.2 to 18.3 mol m(-2) d(-1)), higher CO2 concentration (345 to 623 mumol mol(-1)) and lower plant density (80 to 32 plants m(-2)) hardly influenced stem length (maximum increase of 10%). Nevertheless, the duration of the long-day period (0 to 21 days) and temperature (16 to 28degreesC) are required inputs when predicting stem length, since these strongly enhanced the number of internodes and the average internode length. A module is developed for predicting number of flowers excluding flower buds (NF) based on the total aerial fresh mass per plant (TFM) (NF = 0.210TFM - 1.25). This relationship accurately described NF for highly diverse growth conditions (r(2) = 0.84). In contrast, individual flower size of the fully open flowers did not respond to the assimilate availability showing a rather constant value: 0.21 g flower(-1); 32 cm(2) flower(-1). However, when the incident PAR during the short-day period was under a threshold value (7 mol m(-2) d(-1); i.e. autumn crops) individual flower size decreased linearly with decreasing PAR and higher temperatures resulted in smaller flowers. The practical application of these modules is discussed.