Bulb development in the onion (Allium cepa L.) and the effect of storage temperature on bulb rest

Wherever bulb onions are grown, part of the crop is usually stored. Since the bulbs can be kept for weeks or months, successful storage helps determine their availability as food. It has long been known that onions do not sprout readily soon after harvest, even if the bulbs are planted in moist soil. Such bulbs are said to be in rest. As storage is prolonged, the resting condition disappears and the bulbs sprout easily. Storage conditions, however, may prolong the period of rest and, more important, may retard sprouting and rooting long after rest is past. In this study data are presented on the morphological changes related to rest as the latter is measured by sprout and root production. Bulb growth and development are described for field-grown plants, and changes in bulbs leading to rooting and sprouting are followed during curing and during storage at several temperatures. The capacity of bulbs to root and sprout was measured by removing samples from storage to conditions favorable to bulb growth. Cell divisions in the stem apex were observed during curing and under several storage conditions, to relate stem growth to sprouting. The findings are presented in relation to the practice and problems of onion bulb storage.