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

20 R. M. Madakadze and J. Kwaramba
in tomato fruits and other organs. Pre-storage heating of tomatoes at 38 °C for
3 days can extend their storage life and shelf life (Lurie et al., 1993). There was a
correlation between maintenance of heat – shock protein mRNA during storage
and the inhibition of chilling injury in heated tomatoes. Under certain conditions,
however, heat treatment of tomato fruits may not reduce chilling injury as effectively
as partial ripening (Whitaker, 1994).
4.1.2. Sun scald
Tomatoes at the mature green stage or beginning to show the pink colouration
(breaker stage) are most susceptible to sun scald. The fruits develop a white necrotic
tissue surrounded by a yellow halo. The patch often becomes sunken and wrinkled.
The damage to the fruit occurs on the side or top half exposed to sunlight. The
area may remain white or yellow or become dry and papery and may later become
infected by fungal infection when the fruit ripens. It is caused by a sudden exposure
of the fruit to direct sunlight during hot dry weather and can be worsened by practices
such as pruning or harvesting or other operations involving working moving
through the field and exposing the fruits. Sudden defoliation leads to exposure of
the fruits to sunlight. When supports collapse they expose fruit to direct sun. Heat
and light cause direct irradiation with sunlight. The fruits fail to turn red and in
severe cases turn white and blistered. The exposed side of the fruit turns pale at
first and becomes sunken and wrinkled as the fruit ripens. Temperatures above
35 °C inhibit lycopene (red pigment) formation, while carotene continues to be
produced at temperature of up to 40 °C, causing the tomato to remain yellow. At
temperatures above 40 °C the yellow tissues then turn white.
4.1.3. Catface
This is a typical malformation with deep cavities of the fruit which occurs at the
blossom end of tomato fruit. These can range from mild to extreme deformations
and scarring of the fruit. The fruit will have many bulges and be larger than the
unaffected fruit produced by the same cultivar. Although hereditary, occurrence in
larger fruited cultivars is mainly worsened by exposure of the plant to cool temperatures
at the time of flower initiation. Cultivars may vary in their susceptibility
to this disorder. The large fruited cultivar like Moneymaker is very susceptible. High
nitrogen has also been recorded as a cause for catfacing.
4.1.4. Cracked fruits/Growth cracks
Cracks in tomatoes may radiate from the stem end or may appear in concentric rings
on the shoulders of the fruit. The cracks usually form on unripe fruit often cutting
deep into the flesh. The shallow ripe cracks are known as bursting. This disorder
is hereditary although it is facilitated by continuous rain and heavy dew during
maturity of the fruit. It may extend even into harvesting period when there is frequent
flood irrigation with small amounts of water. Sudden changes in soil moisture and
atmospheric humidity cause this disorder due to alterations in growth rate. It is