| Phalaenopsis orchids are one of the most important potted flowering plants in floriculture. In the first part of our study, we developed a model to simulate the spike elongation of Phalaenopsis `KV Beauty' in response of various temperatures ranging from 15C to 25C. A modified Richards' function was used to predict the daily increment of spike elongation, and the change of parameters' values in relation to the change of temperatures were described with two quadratic functions. The simulation model fitted the observed data fairly well with an R-square = 0.994 in the validation test. The total days required to flower decreased as temperature increased; however, the number of flowers significantly decreased under 21C and 25C. In the second part of our study, we evaluated the effects of two plant growth retardants (paclobutrazol and flurprimidol) on spike elongation of Phalaenopsis `KV Beauty' with different application methods and concentrations. Spraying on the leaves and applying directly to the spikes of 200 mg/L paclobutrazol shortened the total spike lengths by 15% when applied on plants with spikes 7-10 cm long. In another experiment, applying 100 mg/L and 200 mg/L paclobutrazol and flurprimidol on spikes both significantly shortened total spike lengths up to 77% when applied on plants with spikes 1-2 cm. Applying paclobutrazol resulted in shorter internodes between flowers, whereas applying flurprimidol resulted in shorter internodes between the base of the spike to the first flower. Such result indicated that paclobutrazol and flurprimidol had different function mechanisms in shortening plant internodes. Applying flurprimidol directly to the spike could potentially be applied to the industry to control the final spike lengths and to reduce the production costs. |
