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ALTERNATIVE SOURCES FOR PHOTOPERIODIC LIGHTING OF GYPSOPHILA
The need for this comparison arose from the introduction of energy saving lamps, with spectral qualities different from those of the normally applied incandescent lamp.
During day extensions up to 18 hours daylength and dusk to dawn lighting treatments, plants received lighting levels ranging from 0.1 on the opposite of the lamps to 2.0 μmol m-2 s-1 PPF underneath the lamps.
The lamps used were: Incandescent, Low Pressure Sodium, Compact Discharge, Red light emitting diodes, Cool White Fluorescent, Blue Fluorescent, Far-red (incandescent lamps, filtered through blue and orange cinemoid filters), and Red + Far-red (Red fluorescent + orange and blue filtered incandescent).
The experiment with Gypsophila was carried out three times: in the first the plants were grown from August 8 to the end of November 1990, the second from December 22, 1990 to June 15, 1991, and the third from July 31, 1991 to the end of November.
Lighting was started after 2 weeks, 4 weeks and 2 weeks in experiments 1,2 and 3, respectively.
In the first experiment, only plants in the Incandescent treatment were induced to flower, plants from the other treatments remained in a rosette stage.
The rate of elongation (bolting) correlated positively with the lighting level in the Incandescent treatment.
In the second experiment (spring flowering) in all treatments a part of the shoots started to elongate.
However, only in the Incandescent and Red+Far-red treatments the majority of the shoots bolted and flowered, in the other treatments the majority remained in the rosette stage.
In the third experiment, in all treatments plants readily bolted and flowered, only in Blue fluorescent and Red light emitting diodes the rate was a little lower.
Bolting rate correlated positively with the lighting level in all treatments.