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

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