Production Practices and Quality Assessment of Food Crops. Vol. 1

development of chilling injury symptoms and suppressed chilling induced ethylene
evolution in both cultivars of Cucurbita pepo (B + /B t ) and Precocious Caserta (B/B)
squash (McCollum et al., 1991). Fruits stored under 1% O 2 maintained higher
levels of spermidene and spermine than those stored in air indicating that high
polyamine levels are positively correlated with the ability of squash fruits to withstand
chilling stress (McCollum et al., 1991).
4.2.2. Freezing injury
Can occur in vegetables at temperatures below –0.8 °C both in the field and in
storage (Cantwell and Suslow, 2001).
4.2.3. Oedema
Oedema is a physiological disorder of cucumbers and is most frequently found
with pumpkins and winter squash that are subjected to moisture stress. This is
most often associated with uneven availability of moisture when immature fruit
are enlarging. On winter squash rinds the severity may be enough to make the
fruit unmarketable. The fruit surface is often raised with circular shaped lesions
that are corky or ‘crusty’ in appearance and may appear irregularly over the entire
surface, or be limited to for example, the shoulder side exposed to direct sunlight.
The crusty appearance is similar to the appearance of scab on hard shelled fruit,
except that the oedema lesions never appear crater-like or shrunken (Bodnar and
Fitts, 2001). On buttercup squash the corking lesions may be circular, spindle or
apostrophe shaped. While on butternut squash oedema appears as linear growth
cracks usually on the neck portion of the fruit.
4.2.4. Stigma death
The development of female flowers may be affected by temperature. Recent
experience in the Middle Atlantic States and in New England indicates that high
night temperatures (above 20 °C) are associated with failure of female flowers to
open and develop properly (Oregon State University, 2002). The ovaries turn yellow
and then shrivel and the stigma of the unopened flower exhibits black streaks into
the ovary. This reduces the yield of squash.
4.3. Cabbages
Effect of Preharvest Factors 25
Cabbage is a cool season crop belonging to the Cruciferae family. Cabbage is a
very important crop in the temperate regions of the world but it is also gaining
importance in the high altitude areas of the tropics especially for small scale farmers
as it has a fairly long shelf life. Sauerkraut is the main processed product from
cabbages (Yamaguchi, 1983). In most of the tropics, cabbage can also be dried
blanching is necessary before drying. Optimum range of temperatures for growth
of cabbages is 15–20 °C, above 25 °C growth is arrested. Minimum temperature
is 0 °C but cold hardened plants can withstand temperatures as low as –10 °C for