Articles
A MODEL OF THE EFFECT OF DAY AND NIGHT TEMPERATURES ON THE HEIGHT OF CHRYSANTHEMUMS
The model was calibrated by reanalysing previously published data on the effects of day and night temperatures on chrysanthemum plant heights.
Final plant height is regarded as the product of the number of internodes and the average internode length.
Final leaf number is determined as the integral of the rate of leaf production, at any temperature, over the duration of the vegetative phase.
Under constant daylengths, the duration of the vegetative phase (time to flower initiation) was found to be a function of effective temperature; where effective temperature is the sub-optimal temperature equivalent of a supra-optimal temperature in terms of developmental rate.
To predict the mean rate of internode extension, the optimum temperature for internode extension was assumed to be higher during the day than the night.
Consequently, independent effective temperatures for both the day and night periods could then be determined.
The average rate of internodal extension was then found to be quadratically related to the mean of the day and night effective temperatures (referred to as TND). Integration of the rate of internodal extension, for any given TND, over the time to anthesis determined final internode length.
This model, therefore, predicts that DIF temperature treatments are successful because high night temperatures are supra-optimal and low day temperatures are sub-optimal for internodal extension.
The model was validated on two independent data sets.