Journal of the Japanese Society for Horticultural Science
Online ISSN : 1880-358X
Print ISSN : 0013-7626
ISSN-L : 0013-7626
Studies on the Flower Bud Formation in Onion Plants
II. Effects of Physiological Conditions on the Low Temperature Induction of Flower Bud on Green Plants
Yoshihiro SHISHIDOTakashi SAITO
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1976 Volume 45 Issue 2 Pages 160-167

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Abstract

Some experiments were carried out to elucidate the effects of plant size, N-nutrition and defoliation on low temperature induction of flower buds in onion plants.
The results were summarized as follows:
1. Effect of plant size.
As the index of plant size, the diameter of the leaf sheath at its base (abbreviated merely as diameter in the following) was shown to be most appropriate. It was found that the larger the diameter the shorter the period of low temperature exposure required for flower bud formation. Moreover, there was recognized the critical plant size above which plants were able to respond to low temperature and which varied with variety. Thus, in Senshuki (autumn sown variety) the critical size seemed to be 6mm in diameter and plants above 10mm in diameter formed flower bud in response to 30-40 days of exposure to 9°C, which was the most efficient exposure in this variety. In Sapporoki (spring sown variety, which, in consequence, had less chance to be selected against premature bolting), however, the critical size was about 3mm in diameter and plants above 9mm in diameter required no more than 20 days of 9°C exposure for their flower bud formation.
Plant age indicated by the growth period from sowing to low temperature exposure seemed to be less associated with the low temperature requirement for flower bud formation. Plants, irrespective of their age, required different periods of low temperature exposure according to their size.
2. Effect of N-nutrition.
Plants which were inferior in their growth under low N-fertilization formed flower bud following a shorter period of low temperature exposure than plants of rapid growth under high N-fertilization. At first sight this may be inconsistent with the result mentioned above the larger the plant size, the shorter the period of low temperature exposure required for the flower bud formation.
This can be attributed, however, to the high content of carbohydrates as well as to the high C/N ratio in N-deficient plants.
3. Effect of defoliation.
In plants tested, the brades of all leaves were cut off in varying degrees. Plants as large as 11mm in diameter formed flower buds following a comparatively small number of days of low temperature exposure irrespective of the degree of defoliation. While, in plants no more than 8mm in diameter, the more severe the defoliation the more days of low temperature exposure were required for flower bud formation. Our explanation of this result is that the site of the biochemical change which is induced by low temperature and results in flower bud formation is around the leaf bases of inner leaves and materials for such biochemical change, e. g. carbohydrates accumulate enough quantitatively around the leaf bases in large plants before defoliation, but not in small plants, thus, large plants can form flower buds regardless of severe defoliation.

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