Agriculture Reference
In-Depth Information
in crops like cucumber, low radiation
levels give rise to fruit of light green col-
our that soon turn yellowish, something
that is associated with low quality (Vonk-
Noordegraaf and Welles, 1995). Excessive
radiation impinging on cucumber fruit
induces a green colour that is too intense
and a skin that is too thick. In tomato, in
order to achieve a proper colour, growers
prune leaves to favour the penetration of
light to the fruits, in low radiation peri-
ods, or provide various forms of shading
to protect the fruit from intense radiation
and overheating. On the other hand,
greenhouse light-diffusing covering mat-
erials limit intense direct radiation on
the fruits, contributing to improve their
quality.
Unfavourable climatic conditions for
fruit set affect fruit quality. Low tempera-
tures limit fruit set of several fruit vegetables.
In tomato, for instance, low temperatures
induce the formation of irregular fruits,
with bad colour and that are slow to ripen
(Castilla, 1995). Low night temperatures
increase the number of malformed fruits in
pepper.
With high radiation, the temperature of
fruits exposed to the Sun's rays may exceed
the temperature of the air by up to 10°C, as
fruits have very low transpiration, and
exposed fruits may be sunburned. Therefore,
in fruits like tomato it might be necessary to
shade them during periods of high radiation.
The firmness of the fruit decreases
when radiation is low, ambient humidity is
limited and temperatures are extreme: lower
than 13°C or higher than 25°C (Zuang,
1984). These extreme temperatures, same as
excessive day-night thermal differences
(greater than 10°C) negatively influence the
colour of tomato fruits (Zuang, 1984).
It must be remembered that colour and
firmness are frequently antagonistic.
Harvesting before full colouration in tomato,
with good firmness but with lower sugar
content, imposed by the need to send the
product to faraway markets involves subop-
timal organoleptic characteristics for the
consumer (Kader, 1996).
A high ambient humidity limits tran-
spiration, which decreases the calcium
content in the tissues, affecting the quality
of the fruits. A high CO
2
level improves the
quality and quantity of the produce indi-
rectly, as photosynthesis is increased.
In general, climate factors which favour
photosynthesis and, as a consequence, the
synthesis of sugars, improve the organolep-
tic quality of the fruits, because the flavour,
in fruit vegetables, depends primarily on
the sugar and volatiles content, as well as
on the acidity (Hobson, 1988). In melon, for
instance, flavour improves with an increase
in the dry matter content (sugars). In tomato,
an increase in radiation favours the content
of sugars and acids (Urban, 1997a).
6.10.3
Other factors affecting quality
Fruit size is very influenced by the quality
of the fruit set, there being a linear relation-
ship between fruit size and number of seeds,
so an improvement in fruit set will induce
an increase in fruit size (Castilla, 1995). The
vibration of the flowers or the use of bum-
blebees or bees to improve pollination and
fruit set is very beneficial.
The distribution of assimilates, obvi-
ously, is of primary importance in the size
of the fruit. Therefore, cultural practices
must limit the competition for assimilates:
for instance, pruning the tomato trusses to
allow a certain number of fruit which may
achieve proper size or eliminating axillary
shoots that compete with the fruits.
The distribution of assimilates also
affects the shape and uniformity of cucum-
ber fruit, because an excess of fruit induces
a higher number of malformed fruit (Urban,
1997a).
An issue of increasing public interest
during recent years is the absence of phy-
tosanitaries and heavy metals in the com-
mercial product, because the consumer is
demanding safe, healthy and high quality
food (Viaene
et al.
, 2000).
Water and nutrient supply under proper
salinity conditions must be optimized to
achieve a good quality, as they determine
the quality of the harvestable product
together with the genetic characteristics, the
