Agriculture Reference
In-Depth Information
yellow, green or brown spots in which the oil glands of the
skin stand out prominently because of slight sinking of the
tissue between them (Murata 1997). The disorder is well
described by Knight et al . (2002). The incidence of
oleocellosis is closely related to the turgidity of the fruit
during harvest. The application of Ethephon as a pre-
harvest spray to 'Shamouti; oranges at colour-break
reduces fruit damage by oleocellosis (Erner 1982).
that chilling injury might be associated with the balance of
gibberellins (GA) and abscisic acid (ABA); high ABA
levels correlate with drought and chilling injury resistance.
More recently, the role of ABA in protecting fruit from stor-
age disorders has been disputed, with oxidative stress impli-
cated in CI development, and high levels of antioxidants,
such as carotenoids, thought to provide protection (Alferez
et al . 2005). Chilling injury in lemon, grapefruit and other
citrus fruit can be alleviated by temperature conditioning,
intermittent warming, delayed storage with thiabendazole,
imazalil and by film packaging (Murata 1997).
Stem-end rind breakdown
Stem-end rind breakdown (SERB) is symptomatically
similar to the cell collapse that occurs in over-mature rind.
However, SERB often occurs within a week of harvest,
with Valencia oranges especially susceptible (Ritenour &
Dou 2009). A distinguishing feature of SERB is a narrow
band of undamaged rind around the calyx. This area is less
prone to water loss, and subsequent cell collapse, due to a
lack of stomata and thicker wax on the cuticle (Albrego
1972). Minimising water loss after harvest and storing at
cool temperatures (4°C) substantially delay the expression
of SERB (Dou et al . 2001).
Mechanical injury
Wounding fruit contributes to increased decay and poor
quality. Various mechanical injuries can occur from pro-
duction to harvesting, transport, packing, re-packing and
display and provide entry points for post-harvest patho-
gens. The following are the most important mechanical
injury categories:
Impact and compression damage
Damage by direct impact with a sharp or blunt object may
cause impact or compression damage. Mechanical injuries
are often caused by long stems, fingernails, damaged bins
or protruding objects in the packing lines. Small injuries
and impacts also become more obvious during storage due
to dehydration or development of oleocellosis (Taverner
et al . 2009).
Post-harvest pitting
Post-harvest pitting is a similar disorder to rind staining,
and was first described on white grapefruit and 'Falglo'
tangerine. This disorder occurs in waxed fruit, and appears
associated with gas permeability. Navel oranges are prone
to post-harvest pitting, and also express stem-end rind
breakdown-like symptoms that are considered indistin-
guishable from post-harvest pitting (Petracek et al . 2006).
Using more gas permeable coatings and prompt low-
temperature storage, can reduce symptoms.
Brushburn
Damage to the citrus rind by abrasion is more common in
late seasonal fruit and in new pack houses where protrud-
ing corners may expose fruit to wounding. The reddish-
brown marks are associated with raised surfaces on the
rind (Taverner et al . 2009).
Peteca in lemons
Peteca resembles pitting, but the edges of the depressions
are more gently rounded. The outer layer of the rind sinks,
at first without losing its normal colour, and then oil glands
begin to darken (Murata 1997). In lemon, increasing brush-
ing times after harvest induces the incidence of peteca.
Zebra skin
Reddish-brown stripes of the rind of citrus are referred to
as Zebra skin caused by mechanical damage done to highly
turgid mandarin rind through abrasions. These symptoms
are more common when harvesting occurs too soon after
rain or irrigation (Taverner et al . 2009).
Chilling injury
Most citrus fruits, especially grapefruit, limes and pomelos
are chilling-sensitive (Murata, 1988) and develop chilling
injury (CI) symptoms in chilled storage and/or while in
transit. Symptoms of CI in citrus fruit are pitting, discol-
oured patches, superficial brown staining of the rind,
browning of the albedo and watery breakdown. According
to Grierson (2002), fruit produced on drought stressed trees
are very resistant to CI. The mechanism conferring
resistance is not clear. It has been generally considered
CITRUS POST-HARVEST DISEASES
Citrus is attacked by several plant pathogens that can cause
fruit and foliage diseases, root and trunk diseases, systemic
diseases and post-harvest decays. Post-harvest diseases
cause little or no damage to the tree. However, losses from
post-harvest pathogens are economically more significant
to the grower because they represent cumulative costs not
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