zone of their origin combined with breeding for adaptation to new grow-
ing areas. For cultivars suitable for the northern hemisphere, growth and
development slow down and ultimately cease in the autumn due to de-
creasing day length, temperature and solar radiation leading to a stage
of physiological maturity (Watada et al., 1984). Consequently, the rate
of respiration at harvest is low compared with vegetables harvested dur-
ing rapid growth. The storage potential of biennial vegetables is closely
connected to the onset of dormancy in the autumn, which may either be
imposed due to unfavorable growing conditions (carrot, beetroot) or hor-
monally controlled (onion, cabbage), and therefore a true dormancy or
rest. The main part of most storage organs consists of parenchymatous
tissue, and dormancy is therefore probably restricted to the apex and root
primordia. The apex also holds a low temperature vernalization response
with regrowth and sprouting after winter survival. Although the time
span from harvest to sprouting may vary considerably according to cul-
tivar and environment, most biennial vegetables are suitable for long-
term storage (i.e., six months or more) providing the storage conditions
suppress regrowth.
The few research reports available indicate that the postharvest phys-
iology of biennials is controlled via a balance between the common iden-
tified phytohormones, i.e., auxins, gibberellins, cytokinins abscisic acid
and ethylene (Isenberg et al., 1987). This makes correlative, quantita-
tive hormone analyses tedious and difficult to interpret as an estimation
of storability at harvest. During the harvest period the storage organ be-
comes an important sink for carbohydrates and nitrogenous compounds,
which may be used as an indication of the progress of physiological ma-
turity or dormancy. In cabbage cv. ‘Hidena F 1 ’ sucrose content in core
and head leaves almost doubled over the harvest period in the autumn
(Nilsson, 1988), but after mid-October sucrose accumulation leveled out.
A possible reason for these pronounced changes in the carbohydrate
composition is the cessation of differentiation of new leaves in the api-
cal meristem supporting the assumption of a transition to dormancy.
Does the stage of physiological maturity at harvest have any influence
on the storability of cabbage? During the first two months of storage at
2°C, the total amount of soluble sugars in cabbage cores decreased fol-
lowed by a pronounced increase in sucrose content, indicating termination
of the rest period. However, these changes in carbohydrate composition
were only influenced by the time of harvest to a minor degree (Nilsson,
1993). The length of the dormant period during storage seems therefore
not to be determined by the stage of physiological maturity at harvest pro-
vided the apex has entered the dormant period before the first harvest.
Physiology of Storage 113