Agriculture Reference
In-Depth Information
The effects of calcium nitrate sprays during the growing season on fruit
calcium, bitter pit and breakdown in storage in air at
Table
.
◦
C of 'Cox's Orange Pippin' apples
Bitter pit (%)
Fruit Ca
Breakdown
Trial
(mg/
g) External Internal
(%)
. Appleby, New Zealand
Control
.
.
.
.
+
sprays
.
.
.
.
+
. Teynham, Kent, UK
Control
.
.
.
.
sprays
.
.
.
.
. Hadlow, Kent, UK
Control
.
.
.
sprays
.
.
.
Total Ca(NO
)
applied in kg ha
−
: Trial , ; Trial , ; Trial , .
+
Included watercore and watercore-breakdown.
From Sharples (
). Reproduced with permission.
Calcium and physiological disorders
There are a number of physiological disorders of apples, that can develop
in the orchard or only become evident after a period of storage, which are
associated with low fruit tissue calcium.
Bitter pit is perhaps the most important of these (Table
). The primary
symptomisdiscretepittingofthecorticalflesh.Thepitsarebrownandbecome
desiccated. They are mostly in the outer cortex, frequently just under the skin,
and the collapse of the outermost cells causes small depressions. Pitting may
also occur deep in the flesh and only become visible when the fruit is cut.
Frequency of pitting is often greater towards the calyxend (Faust and Shear,
.
). The first sign of bitter pit is collapse of the
cell walls and by the time that pitting is visible to the naked eye plasmolysis of
the cytoplasm has occurred. The pit cavities result from the collapse of several
cells and are bound by the remains of the original cell walls (Smock and Van
Doren,
; Ferguson and Watkins,
). Within the fruits bitter pit is most common in those zones with
the lowest Ca concentration although the lesions themselves do not show a
low Ca content.
There is sometimes a closer correlation between the incidence of calcium-
related storage disorders to the ratio of Ca to K or K
+
Mg than to Ca alone
(Holland,
) concluded that fruits with low
Ca become more susceptible to bitter pit, lenticel blotch pit and cracking as
potassium and magnesium concentrations increase. Low-oxygen stored fruit
have a lower threshold level of Ca at which bitter pit is avoided than have
air-stored fruit (Sharples and Johnson,
; Waller,
). Perring (
) stated that for 'Cox'
in England avoidance of lenticel blotch pit, bitter pit, loss of firmness and
). Rowe (
