Articles
APICAL DISSECTION AND LIGHT-INTEGRAL MONITORING AS METHODS TO DETERMINE WHEN LONG-DAY INTERRUPTIONS SHOULD BE GIVEN IN CHRYSANTHEMUM GROWING
To aid the timing of this, two methods, apical dissection and light-integral monitoring, were assessed as possible alternatives to the generally used ‘calendar’ approach.
The test procedures involved the transfer at intervals of plants of three widely-grown cultivars, Snapper, Snowdon and Pink Gin, from short-day to non-inductive, long-day conditions to give a measure of the basipetal progression of commitment to flowering that had occurred up to the time of transfer.
There was a time lag of some days between the irreversible commitment of lateral buds to flower and the visual detection, using a microscope, of morphological changes indicating that initiation had occurred.
The stage of development of the terminal flower bud had, therefore, to be relied on as an indicator of lateral bud commitment.
However, this relationship was too variable to be of practical value.
Uncontrollable variation in light receipt was found to limit severely the precision with which the speed of bud initiation of a given cultivar could be judged.
To improve the timing of interruptions, empirical relationships between the time to induce all buds and the average daily light (PAR) integral (and average daily total solar radiation integral) were determined for each of the three cultivars.
These relationships were then tested by transferring plants from short days to continuous long days on the predicted day and up to six days before and after.
Promising results were obtained with flower induction completed by the predicted date in all cases.