Tomatoes - Crop Post-Harvest: Science and Technology - page 8

adequate fruit growth rate and (9) spraying of young
expanding fruit with 0.5-0.65% calcium chloride solution.

generally associated with the rapid movement of water
and sugars towards the fruit when cuticle elasticity and
resistance are weak (Dorais et al . 2001); there are
differences in cultivar susceptibility, but the problem can
be reduced by adequate calcium nutrition and avoidance
of drought stress (Hao et al . 2000a). Fruit with high soluble
sugar content is more susceptible to cracking, due to the
greater pressure applied against the cuticle. Another cause
for cracking is imbalance between the supply and loss
of water, and therefore cultivars with a highly developed
system of vascular tissue are more resistant to cracking
(Cotner et al . 1969). Gibberellic acid application was
reported to reduce tomato fruit cracking (Peet 1992). This
effect is probably due to alteration of the calcium dynamics
at the level of the pericarp (Bush et al . 1989), and an
increased elasticity of the cuticle (Larson et al . 1983).

Blotchy ripening
Blotchy or irregular ripening is characterized by green
and green-yellow areas on apparently normal red, ripe fruit
(Plate 2.4). It is usually confined to the outer pericarp
walls, but in extreme cases radial walls can also be
affected. Blotchy areas of fruit walls contain less organic
acids, dry matter, total solids, starch, sugars and nitroge-
nous compounds. Low potassium (Adams et al . 1978) and
high fruit temperature (a temperature of >30°C affects
pigmentation) are believed to be related to blotchy
ripening. The cause of blotchy ripening is not fully under-
stood, but is thought to be related to low light intensity,
cool temperatures, high soil moisture, high nitrogen and
low potassium or combinations of those factors. Tomato
varieties differ in their susceptibility to this disorder.

Greenback or green shoulder
This is a different disorder from blotchy ripening. The
symptom is characterised by a persistent, firm green area
around the calyx end due to undegraded chlorophyll, while
the rest of the fruit is ripe and red in colour. The green
area may turn yellow and thus be called 'yellowback' or
'yellow shoulder'. This is generally thought undesirable,
but in some countries such as Cuba and Taiwan it is actually
preferred by some consumers. This disorder is genetically
controlled and can be abolished by incorporating the
'uniform ripening' gene (Grierson & Kader 1986).

Cracking and russeting
Tomato cracking can cause up to 35% losses in North
American greenhouses (Dorais et al . 2001). Greenhouse
tomatoes are more vulnerable to fruit cracking compared
to field-grown tomatoes because greenhouse tomatoes are
usually harvested later at the pink stage or beyond, and
most greenhouse tomato cultivars lack cracking resistance.
Fruit cracking not only reduces fruit appeal and marketing,
but also can increase fruit susceptibility to decay and
shorten shelf life. Cracking and splitting of tomatoes are
usually initiated before harvest, generally about seven
weeks after fruit set (Bakker 1988). Several types of
cracking are known to affect tomatoes, including cuticle
cracking (russeting), fruit bursting, radial cracking and
concentric cracking. Cuticle cracking, fine cracks on the
skin which impair quality and reduce shelf life, is the
most common type in greenhouse tomatoes (Dorais et al .
2001). Cuticle cracks are usually initiated as small fissures
in the outer epidermis and occur at right angles to the
direction of expansion of the epidermal cells. In later
stages, the complete epidermis and part of the underlying
collenchyma tissue break down. Russeting was suggested
to occur because the expansion of the epidermis could not
keep pace with fruit enlargement. Higher numbers of fruit
per plant decrease the incidence of cuticle cracking by
increasing the competition among fruit for carbohydrates,
and reducing the supply of sugars and water to the fruit.
A fruit:leaf ratio of 1.24:1 to 1.28:1 is considered optimal
for controlling russeting (Dorais et al . 2001).
The intensity of fruit cracking depends on cultivar, time
of the year and environmental conditions. Fruit cracking is

Gold fleck, gold speckle or pox syndrome
These are tiny, yellowish spots of less than 0.1 mm across
occurring immediately below the epidermis, visible on ripe
fruit and mostly affecting the proximal half of the fruit
(Ilker et al . 1977). The disorder is associated with the
formation of calcium oxalate crystals in the affected cells
(De Kreij et al . 1992). This disorder affects the external
appearance of the fruit (Goossens 1988), and it reduces its
shelf life (Janse 1988) due to the eventual development
of tan, ruptured, necrotic lesions (Ilker et al . 1977).
Symptoms are commonly affected by those factors of
cultivar, nutrition and growing environment that favour
calcium transport to the fruit.

Hollowness, puffiness or boxiness
This disorder is characterised by lack of gel tissue
surrounding the seeds, and open cavities between the
outer pericarp walls and the locular contents in one or
more locules (Plates 2.5a, b) (Grierson & Kader 1986). The
affected fruit tend to be light in weight and become soft,
and can be detected by flotation in water. The symptoms