The infected area of the fruit is at first firm and brown,
but subsequently the peel tissue softens and fluid is released. As the fungus
grows it results in a white cottony look to the surface of the fruit. Decay
spreads by contact of an infected fruit to all surrounding healthy fruit in the
container. Postharvest Disorders Chilling Injury Lemon fruit are susceptible to
low temperature injury, commonly known as chilling injury (CI), if held at
temperatures below 10°C (50°F). CI is a physiological disorder which adversely
affects the appearance and quality of the fruit. Fruit symptoms include pitting
and sunken lesions on the peel surface, skin discolouration, staining of the
membranes separating the segments, decay, and off-flavour of the pulp. Damage
is a function of temperature and time, with more CI incurred at lower
temperatures and longer exposure durations. The use of pre-harvest applications
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regulator gibberellic acid reduces susceptibility to CI, as does maintenance of
a very high RH (>95%) storage environment. Preconditioning lemons by holding
the fruit at ambient temperature for several days before storing at chilling
temperatures will also reduce injury. Waxing the fruit and a postharvest
fungicide application will lower the amount of damage and decay from CI.
Oleocellosis Oleocellosis, or oil spotting, is a result of mechanical damage to
the peel. The outer portion of the lemon fruit contains oil glands which are
rich in oil and terpenes. When the oil glands are ruptured, the oil and
terpenes leak out and are toxic to the surrounding cells. This results in death
of the adjacent epidermis and the formation of irregularly shaped yellow,
green, or brown spots in which the oil glands of the skin stand out prominently
because of slight sinking of the tissues between them. Turgid fruits are most
likely to have oleocellosis because their oil glands are more easily ruptured.
Fruit turgidity is greatest in the early morning and under very humid, wet
conditions. Harvesting under such conditions or while dew is on the fruit
should be avoided. Fruit Figure 11. Cottony rot of stored lemons. 12 should be
picked when the fruit surface is dry and should be handled carefully so that
oil glands are not punctured or ruptured. Oleocellosis can be minimized by
picking fruit in the afternoon of sunny days, waiting to harvest 2 or 3 days
after a rain or an irrigation, using padded harvest containers, and having
pickers wear cotton gloves. Lemons may also be left in the field overnight in
their harvest container to allow the turgor pressure to decline. The lower
fruit turgor pressure permits safer transport to the packing area. Peteca
Lemons may develop ( citrus packing machine), ( Orange packing machine ), (
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large sunken areas of the rind or pits soon after packing. Peteca is a type of
rind pitting in which the edges of the depressions are gently rounded. The
outer layer of the rind sinks, at first without losing its normal colour, but
eventually the oil glands begin to darken. Heavy brushing of the peel increases
the incidence of peteca. Also, storage of lemons at 100% RH will significantly
increase the amount of peteca. Although the cause of peteca is not known with
certainty, it is thought that heavy oil sprays prior to harvest can increase
the severity of this disorder. Lemons should not be subject to excessive
brushing and should be waxed with a carnauba based wax.
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