Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
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however, more severe when foliage is sparse as exposed fruits crack more due to<br />
exposure to greater temperature fluctuations from exposure to direct sun rays.<br />
Tomatoes grown under cold conditions are more prone to cracking. Temperatures<br />
below 10 °C encourage the condition as well. High nitrogen <strong>and</strong> low potassium result<br />
in succulent plants that produce tomatoes that are very susceptible to cracking.<br />
4.1.5. Blossom end rot (Black bottoms)<br />
Effect <strong>of</strong> Preharvest Factors 21<br />
Blossom end rot arises from a localized deficiency in calcium at or near the blossom<br />
end, which could be facilitated by several environmental conditions. It is also<br />
associated with fluctuations in the soil moisture due to incorrect or poorly scheduled<br />
irrigation <strong>and</strong> poor root development. A brown-black, dry, leathery depression<br />
at or near the blossom end occurs during development <strong>of</strong> the fruit commonly<br />
noticeable when the fruits are one-third to one-half full size. Occasionally it appears<br />
on the side <strong>of</strong> the fruits <strong>and</strong> sometimes produces internal black lesions not visible<br />
from the exterior <strong>of</strong> the fruit. Affected fruits ripen more rapidly than normal fruits.<br />
At first a small water soaked light tan spot appears, enlarges <strong>and</strong> darkens as the<br />
fruit size increases. The spot may enlarge to cover as much as a third to half <strong>of</strong><br />
the entire fruit surface. Large lesions soon dry out <strong>and</strong> become flattened, black<br />
<strong>and</strong> leathery in appearance <strong>and</strong> texture. This is due to environmental conditions<br />
that cause water stress.<br />
In hydroponic culture the supply <strong>of</strong> Ca 2+ is usually more than adequate for plant<br />
development <strong>and</strong> is unlikely to be the primary cause <strong>of</strong> blossom end rot, however,<br />
the uptake <strong>of</strong> Ca 2+ can be reduced by high EC, poor aeration or adverse temperature<br />
<strong>of</strong> the root zone. Root cooling to 17 °C in plants grown in rockwool mats<br />
reduced blossom end rot incidence <strong>and</strong> increased the Ca 2+ content <strong>of</strong> the fruits<br />
(Benoit et al., 2001).<br />
Transport <strong>of</strong> Ca 2+ to the fruit is intrinsically low, as most <strong>of</strong> the Ca 2+ is transported<br />
to leaves by canopy transpiration. A combination <strong>of</strong> low uptake <strong>and</strong> low<br />
transport <strong>of</strong> Ca 2+ to the fruit can cause a low Ca 2+ status in the fruit (Ho et al., 1999).<br />
Environmental conditions required for high yield, such as light, carbon dioxide<br />
concentration <strong>and</strong> temperature stimulate fruit expansion, but may not increase <strong>and</strong><br />
may even reduce the transport <strong>of</strong> Ca 2+ to the distal tissue <strong>of</strong> the fruit. Incidence <strong>of</strong><br />
blossom end rot is determined by the fruit growth response to the environmental<br />
conditions during the rapid phase <strong>of</strong> fruit enlargement.<br />
Symptoms <strong>of</strong> blossom end rot may not be entirely caused by low Ca 2+ in the<br />
fruit tissue itself, but its interactions with N <strong>and</strong> P in maintaining the cell membrane<br />
permeability <strong>and</strong> cell wall structure. In an experiment carried out to determine the<br />
influence <strong>of</strong> N source, N application rate <strong>and</strong> soil moisture on the incidence <strong>of</strong><br />
blossom end rot, a close relationship was observed between the incidence <strong>of</strong> blossom<br />
end rot <strong>and</strong> the ammonia concentration in the soil solution (Morikuni <strong>and</strong> Shimada,<br />
2001). In soil where nitrification had been delayed, the unnitrified ammonia was<br />
likely to suppress Ca 2+ absorption <strong>and</strong> induce blossom end rot. When only nitrate<br />
N was applied the blossom end rot was decreased. A relationship was clearly<br />
observed between the incidence <strong>of</strong> the blossom end rot <strong>and</strong> Ca 2+ concentration in<br />
petiole sap from the leaf near the trusses, just after blooming. When Ca 2+ concen-