The present studies were designed to elucidate the effects of application of growth regulators on the low temperature induction of flower buds in onion plants cv. ‘Sapporo-ki’.
1. Plants were treated with daminozide (SADH) at 2, 000ppm, with ethephon at 500 and 1, 000ppm and with gibberellin (GA3) at 100ppm before low temperature (9°C) exposure.
Both the plant growth and induction of flower buds were suppressed a little by SADH, while strongly by ethephon. On the contrary, GA3 increased the number of leaves and hastened the induction of flower buds.
2. In the plants with leaf sheath diameter of 10mm, the minimum duration of low temperature exposure required for the induction of flower buds was about 20 days and little affected by GA3, but in the plants with leaf sheath diameter about 7mm, it was 40-50 days and shortened to about 20 days by GA3.
3. GA3 was effective in the induction of flower buds when it was applied before or during the low temperature exposure, but it was ineffective when applied after the low temperature exposure.
It seems that GA3 hastens the flower bud formation through its effect on the activation of meristematic tissues and not through taking the place of low temperature in its effect.
