Agriculture Reference
In-Depth Information
apparent. Shatter bruise increases with high
tuber turgidity and temperatures below 10°C
(Smittle
et al
., 1974).
Pressure bruises develop in storage and are
flattened or slightly sunken areas on the tuber
where it has been in contact with other tubers or
solid surfaces. When relative humidity is below
95%, the external pressure causes the affected
tissue to lose water and become flattened. The
depression will persist if storage relative humid-
ity remains below 90%. Internally, tissues may
exhibit gray to black discoloration, usually more
intense in the vascular region (Olsen
et al
.,
2003). Warm storage temperatures, excessive
potato pile height, and long storage favor pres-
sure bruise.
Bruise damage is minimized by careful har-
vest of tubers that are not too cold and of the
proper hydration level. To ensure adequate hy-
dration at harvest, follow good cultural practices
to promote proper vine and root growth. Supply
adequate potassium nutrition. If the soil is dry,
and irrigation is available, apply a light irriga-
tion to soften soil clods, reduce abrasion, and in-
crease tuber hydration. Tuber pulp temperature
should be between 10°C and 15°C. Avoid har-
vesting when pulp temperature is below 7°C and
above 18°C. Adjust harvesting equipment to
minimize drop heights and add padding to areas
known to damage tubers. During harvest, keep
conveyors full of tubers to help reduce roll back.
The use of a canvas sling in bulk trucks helps to
reduce drop height from the boom into the truck.
Control of pressure bruise includes main-
taining storage relative humidity above 90%, piling
tubers not more than 5.5 m high, and holding
tubers at the optimum storage temperature.
wound periderm, as in hollow heart, but with
gray or black layers, and is referred to as a “cat's
eye” (Strand, 2006). Only in extreme cases are
there visible external symptoms of moist, discol-
ored patches (Snowden, 1992).
Blackheart is the result of inadequate oxy-
gen supply. It develops when internal tuber tis-
sues do not receive enough oxygen to support
respiration (Davis, 1926). Oxygen deficiency
may be due to inadequate ventilation in closed
storage bins or transport vehicles, or exposure of
tubers to near freezing or greater than 32°C
temperatures. At high and low temperatures,
gas diffusion is too slow to reach the internal
tuber tissues. At lower temperatures, longer
times are required for blackheart to develop
(Stewart and Mix, 1917). In the field, high soil
temperatures and waterlogged soils contribute
to blackheart development. Tubers will not re-
cover once blackheart has developed. Seed
tubers that have blackheart should not be planted,
due to increased susceptibility to soft rot and
poor emergence problems (Wale
et al
., 2008).
Some potato cultivars tolerate conditions of
low oxygen better than others, but precautions
must be taken with all potatoes. Avoid planting
potatoes in poorly drained areas. Harvest tubers
from hot, dry soils as soon as the vines are dead.
After digging, do not leave tubers lying on hot,
dry soils (O'Brien and Rich, 1976). Provide good
ventilation in storage and transit. Avoid expos-
ing tubers to temperatures greater than 32°C or
prolonged near-freezing storage.
14.12 Translucent End/Jelly End
The disorder, translucent end, is also known as
sugar end, glassy end, incipient jelly end, or dark
end. In affected tubers, the stem end contains
higher reducing sugars (glucose and fructose)
and lower dry-matter content than the bud end
(Iritani and Weller, 1973; Sowokinos
et al
.,
2000). The tissue appears translucent or water
soaked. Usually, less than 5 cm of the stem end is
affected (Strand, 2006). When processed into
chips or French fries, heat during processing
causes the reducing sugars to react with amino
acids and form undesirable dark compounds.
This disorder is sometimes referred to as dark
end, because one end of the French fries made
14.11 Blackheart
The term “blackheart” describes a sharply delin-
eated, purplish-gray to black area in the center
(pith) and closely associated parenchyma cells of
the tuber
(Fig. 14.5
)
. Occasionally, the discolor-
ation radiates to the skin. The black discolor-
ation of blackheart is due to melanin, the same
pigment responsible for blackspot bruise (Reeve,
1968). The affected tissue is usually firm and
has no odor. A cavity may form if the affected
tissue shrinks. This cavity is not lined with
