Articles
EFFECTS OF TIMING AND DURATION OF A TEMPERATURE DROP IN RELATION TO SUNSET ON SHOOT ELONGATION OF POTPLANTS AND BEDDING PLANTS
Two similar experiments were carried out in climatized daylight chambers, starting on November 3 and February 25. Seven temperature strategies were applied, a 4-hr temperature drop starting at 8, 12, 16 and 20 hours after sunset, an 8-hr temperature drop starting 8 and 16 hours after sunset and a control.
Short-day, long-day and day neutral species were investigated.
Daylength was 16 hours in all temperature treatments, photoperiodic lighting began with fluorescent lamps 8 hours after sunset until 2 hours after sunrise.
In the first experiment, elongation growth of all four crops was most sensitive to temperature drop 16 hours after sunset.
For Begonia hiemalis ‘Rosanne’ and Impatiens New-Guinea ‘Thecla’ a 4-hour period of low temperature was as effective as an 8-hour period which began 16 hours after sunset (a full ‘DIF’ in this period of year). For Fuchsia ‘Dollar Princess’ and Pelargonium zonale ‘Pulsar red’, the 8-hour period, starting 16 hours after sunset, was more effective than 4 hours low temperature in the same period.
In the second experiment, elongation growth of Impatiens and Fuchsia showed similar reponses to temperature drop as in the first experiment.
However, at this time of the year, the period of 16 hours after sunset falls in the middle of the day. Begonia and Pelargonium responded only slightly, and not similarily, to the applied temperature strategies in this experiment.
From this study, it is concluded that the effects of a short period of low temperature on elongation growth appears to be related to sunset (or start of the long-day treatment). However, other factors interfere with the temperature response, such as the level of irradiance.
Effects of temperature drop were most pronounced under the marginal light conditions of the winter season.
A relationship with the photoperiodic requirements for flowering of any plant was not found in this study.
Possibilities for application of temperature drop in practice are crop dependent.