Compared with cabbage cores, the sucrose/hexose ratio in carrot roots
increases over the harvest period but with minor changes in total soluble
sugars. This behavior has been proposed as an indication of the degree
of “physiological maturity” (Phan and Hsu, 1973; Fritz and Weichmann,
1979; and Nilsson, 1987). Carrots with a high sucrose/hexose ratio should
therefore be more suitable for long-term storage. However, until present,
no clear evidence has been reported to support this hypothesis. Probably,
carrot roots do not enter to a period of true dormancy compared with
onion bulbs and cabbage, which means that the composition of soluble
carbohydrates should not indicate the termination of growth.
Onions are reported to enter into a true dormancy in the autumn (Ab-
dalla and Mann, 1963). Hormonal changes inducing the dormant period
are initiated while the onion is maturing in the field. In northern Europe,
onions are harvested when the necks start bending and are left to dry in
the field for about 10 days before being stored at low temperatures. Con-
sequently, leaf senescence is advanced and the foliage dies back with a
translocation of carbohydrates and free amino acids down to the bulb
(Nilsson, 1980). Growth inhibitors synthesized in the leaves during ter-
mination of growth are, according to Stow (1976), translocated to the
bulb and responsible for initiation and maintenance the bulb in a stage
of dormancy. Too early harvest and leaf desiccation of the bulbs there-
fore may result in earlier sprouting due to too low a level of inhibitors
in the bulb. Compared with cabbage, the carbohydrate composition of
onion bulbs was equal whether harvested early (35% foliage of total
plant weight) or late (2% foliage of total plant weight) (Nilsson, 1980).
The storage life of onions is mainly limited by sprouting. Breeding
for delayed sprouting is one possible way (Miedema, 1994) since the
use of artificial antisprouting compounds, e.g., maleic hydrazide, a chem-
ical applied to the onion leaves when they are green and exporting pho-
tosynthates, will become banned in most countries. The use of ethereal
oils for sprout suppression during storage of potatoes (Aliaga and Feld-
heim, 1985) seems more promising and should be investigated for veg-
etables as well.
PATHOLOGY
While the discussion in this chapter has focused on physiological
changes during storage, an important problem related to long-term stor-
age of vegetables is the incidence of various pathogens during storage.
Postharvest infection often originates from inoculumn that has built up