Agriculture Reference
In-Depth Information
between climate, nutrition and tree vigour. Bitter pit
symptoms often occur prior to harvest, or after long-term
storage.
The disorder starts internally, but as it worsens external
blemishes develop on the skin (Plate 5.3). Badly affected
flesh often has a bitter taste, hence the name. Small bruise-
like spots, which may be darker than the surrounding
tissue, develop on the skin. As the disorder worsens the
spots become brown and sunken to form pits and dry out to
become tough and spongy. Spots usually develop first at
the calyx end of the fruit, but highly susceptible varieties
can be damaged right up to the shoulder. Even fruit with no
obvious symptoms at harvest can develop skin pitting in
storage, resulting in unexpected loss.
Bitter pit can be managed with pre- and post-harvest
control measures (Ferguson & Watkins 1989). Calcium
uptake can be influenced by several pre-harvest factors
such as water availability, climatic factors, nutrition, tree
vigour and crop regulation. Variety and good tree manage-
ment is critical to avoid bitter pit. For example, light
cropping normally promotes bitter bit by influencing the
level of nutrients in the fruit but uptake is also influenced
by water stress. During stress conditions, the leaves retain
water at the expense of the fruit and so calcium goes to the
leaves rather than the fruit (Sharples 1975). Post-harvest
calcium dips are also an effective management tool to
control the disorder.
skin and tissue diffusivity and/or increase fruit susceptibility
to elevated CO
2
and low O
2
.
In contrast, flesh browning in 'Fuji' apples is usually the
result of CO
2
injury. 'Fuji' apples are more sensitive to
high CO
2
than many other apple varieties (Volz
et al
. 1998).
The susceptibility to CO
2
damage in 'Fuji' apples can be
predicted from a sample of fruit held at 20°C at 20% CO
2
and then flesh browning symptoms are observed in
susceptible fruit after three days. These symptoms are
reported to take up to 24 days to develop in controlled
atmosphere storage (Volz
et al
. 1998).
In 'Cripps Pink' apples there are three types of flesh
browning disorders that represent many of the symptoms
discussed earlier (Jobling
et al
. 2005; James
et al
. 2005,
2006). The first is a CO
2
injury that appears to be similar to
CO
2
injury in other apple varieties. CO
2
injury in 'Cripps
Pink' apples is aggravated by controlled atmosphere (CA)
conditions with increasing levels of CO
2
and decreasing
levels of O
2
causing most damage (Jobling
et al
. 2005;
James
et al
. 2005). The effect of CA conditions on the
incidence of CO
2
injury has been previously observed in
other apple varieties (Park & Lee 1992; Johnson
et al
.
1998; Argenta
et al
. 2000). The second type of flesh
browning is called radial flesh browning (RFB) which
appears to be similar to a type of senescent or vascular
breakdown described in other apple varieties (Meheriuk
et al
. 1994) and is aggravated by low seasonal tempera-
tures, late harvest, low storage temperatures and elevated
CO
2
in CA storage (Plate 5.4A). The third type of flesh
browning is called diffuse flesh browning (DFB) and this
disorder is reported to be the result of chilling injury (Plate
5.4B). Similar chilling injuries have been observed in other
apple varieties such as 'Cortland' apples which have been
found to be sensitive to low temperatures in storage but
relatively insensitive to increased CO
2
in the storage
atmosphere (DeEll & Prange 1998).
Interestingly, seasonal climatic conditions have also
been found to influence the development of these three
types of flesh browning in 'Cripps Pink' apples (James
et al
. 2005). The critical periods at this stage appear to be
the first 50 DAFB with cooler seasons promoting the
development to denser fruit and this can increase the risk of
fruit developing RFB in storage. Seasonal accumulated
GDD have also been related to the development of storage
disorders of other apple varieties (Lau 1998). For 'Cripps
Pink' grown in Australia, fruit in seasons or districts with
accumulated GDD below 1200 appear to be susceptible to
diffuse flesh browning and in areas or seasons where the
accumulated GDD are between 1200 and 1500 the fruit are
susceptible to radial flesh browning and all fruit are
Flesh browning disorders
There are several internal flesh browning disorders of
apples and often they are variety specific. Flesh browning
results from a range of pre- and post-harvest factors such as
CO
2
injury, chilling injury, nutrient deficiency or senescent
breakdown. The following are a few examples of some of
the types of flesh browning storage disorders seen in
apples.
Braeburn browning disorder (BBD) is an internal brown-
ing disorder related to seasonal conditions affecting fruit
density that can result in CO
2
injury in storage (Lau 1998).
Research into BBD has shown that the rapid establishment
(within 2-3 days) of CA (1.2% O
2
and 1.0% CO
2
) increased
BBD relative to air storage after cool but not warm seasons.
Another important seasonal predictor is the accumulated
growing degree-days (GDD) above 10°C from full bloom
to harvest. The GDD is a mathematical calculation of the
number of hours per day above 10°C and this is an
indication of how warm or cold a season has been, BBD
develops in regions with less than 1300 GDD above 10°C
from full bloom to harvest. Lau (1998) proposed that cool
growing conditions may alter cellular metabolism, reduce
