1964 Volume 33 Issue 1 Pages 46-52
1. The present study has been conducted to investigate the effect of the length of short-day period before bulbing and the length of long-day period before harvest on bulb formation and sprouting of planted bulbs, and to elucidate the relation between the process of bulb formation and regularity of bulb structure in onion.
2. Under favorable conditions for bulbing in onion (long-day and warm temperature) growth of leaf blade was inhibited. Then about 25-30 days after the beginning of long-day period the stop of production of new leaves and ceasing of growth of the youngest leaf were observed.
3. Basing on the results of investigation in these experiments an intimate relation was recognized among the storage leaf formation, ceasing of leaf growth and falling over of top in onion plants. Whenever conditions became favorable for bulb formation, storage leaves were found in the bulb after 20-30 days, about 10 days before ceasing of leaf growth, followed by falling of the top 20-30 days later.
4. A short-day treatment was given to onion plants prior to their bulbing period and their bulb formation was observed.
The short-day treatment for about 30 days before bulbing period caused an acceleration of growth in onion plants and produced large bulbs. But, in plants under short-days until the initiation of the first tiller bud in the bulb, doubling occurred in many cases.
5. The number of storage-, sprout- and foliage- leaves in a bulb was little influenced by the length of long-day period prior to harvest time. But when the long-day period was below 30 days, the number of storage leaves decreased.
Accordingly, it seemed that a bulb is not formed from definite leaves like tulip, but the regularity of bulb structure in onion is caused by the metamorphosis of leaves in response to the environmental conditions.
6. In planted bulbs the date of sprouting was influenced by the time of their bulbing; the earlier the date of falling, the earlier the sprouting.
Accordingly, it is considered that as the top fell over the bulb enters into dormancy and after a certain period the dormancy of the bulb is broken.