Physiological studies on the bulbing and dormancy of onion plant. IX.

Abstract

The relationship between dormancy of bulb and the properties of its juice was pursued by using the general methods available for study on the seed dormancy.1. The color reaction to tetrazolium was observed only on the terminal part of stem disk in rest bulbs and on the all part of section in sprouted ones. This result suggests that the terminal bud is active and the other part of bulbs inactive during rest. Consequently it appears that rest is a suspension of growth of terminal bud caused by either the shortage of substances available for growth or excess of growth inhibiting substances translocated from thickened leaf sheaths.2. Fresh juice from rest bulbs remarkably inhibited both germination of various seeds and growth of onion seedlings. This inhibiting action of onion juice was not so severe with water-imbibed seeds as with dry seeds. And further it was removed by washing them with running water, but their germination percentage was still low as compared with that of water-incubated seeds.The inhibiting action and pH of onion juice did not change by heat treatment.These results showed clearly that the inhibiting action of onion juice is due to both chemical and physical properties of it.3. It was shown that the inhibiting action of onion juice gradually decreased with increase in number of days after harvest during storage at room temperature, that is, the seed germination was remarkably inhibited with each juice prepared from various part of rest bulbs, but was slightly inhibited only with juice from inner part of sprouted ones.This tendency was promoted by unfavorable storage conditions, i.e. wet moisture and oxygen supply.4. Onion juice prepared from Ohshu, a late variety, showed stronger inhibiting action than that of Senshu-ki, a meduim variety.5. It may be safely concluded from these results that the lowering of inhibiting action of onion juice significantly correlates with earliness of sprouting in bulbs.