Agriculture Reference
In-Depth Information
may be more important to IBS susceptibility, and
not the concentration of a single mineral.
The frequency and severity of IBS are in-
creased with high day and night temperatures
early in the growing season, together with low
rainfall (few rain events) (Sterrett et al ., 1991a,b;
Yencho et al ., 2008). IBS may be more common
on sandy soils (O'Brien and Rich, 1976), which
have low cation exchange capacity and great
heat conductance. Growing location also influ-
ences the incidence and severity of IBS (Sterrett
and Henninger, 1991; Sterrett et al ., 1991a).
To reduce the incidence of IBS, when pos-
sible, plant less susceptible cultivars. Ensure ad-
equate calcium level in the stolon and tuber
zone, especially on sandy or low-calcium soils.
Delaying planting reduces the incidence of IBS
(Iritani et al ., 1984; Sterrett et al ., 1991b), pos-
sibly by mediating tuber size. In warmer cli-
mates, time planting to mature the crop before
excessive heat is expected. Prevent exposing
tubers to high soil temperatures at harvest.
Closer plant spacing may be used to limit the
production of large tubers and reduce IBS
(Creamer et al ., 1999). Maintain adequate soil
moisture through irrigation, mulching, and full
canopy, and use cultural practices that promote
uniform, unstressed vine and tuber growth.
temperatures is only visible once the tubers
have warmed or thawed. The damage that oc-
curs on thawing is from intracellular ice crys-
tals rupturing cell membranes. Tubers killed by
freezing become soft, watery, and exude much
liquid. These tubers disintegrate rapidly in a
watery rot, and are often colonized by bacteria.
In a cold or dry environment, frozen tubers
thaw into a mealy, granular, chalky mass
(O'Brien and Rich, 1976). In the field, freezing
usually occurs on the end or side of the tuber
closest to the soil surface, usually the bud end.
In partially frozen tubers, there is a distinct
purplish to brownish line of corky tissue be-
tween healthy and damaged tissues.
Shorter exposures to temperatures just at
freezing or brief exposure below the freezing
point are marked by several types of internal
discoloration. There are no external symp-
toms, and tubers must be cut open to see the
damage. Tissues at the stem end and vascular
ring are most susceptible to this low-temperature
or chilling injury (Thornton, 2001b). A  net
type of necrosis may develop where the phloem
is blackened and dark strands and necrotic
spots are scattered throughout the tuber tissue.
Blue-gray or black discolorations or blotches
may be present in the vascular ring and associ-
ated tissues. The vascular ring may break
down. Irregularly shaped, opaque bluish-gray
to black patches or diffuse smoky areas may
develop anywhere in the tissues. Tubers with
low-temperature injury, even those that ap-
pear to be only slightly injured, should not be
used for seed, as germination may be delayed
or very poor.
Exposure to cold, non-freezing (0-3°C) tem-
peratures may also lead to tuber injury. Starch is
converted to sugars at these temperatures, caus-
ing the tubers to be sweet. Mahogany browning,
where affected tissues turn gray or reddish-brown,
is a disorder induced when tubers are exposed to
temperatures slightly below freezing (Thornton,
2001b). Tubers held close to 0°C in long-term
storage may develop external dark brown, slightly
sunken areas that are predisposed to surface
mold. Areas under the surface lesions vary from
reddish-brown to dark brown. In some cases, dis-
colored areas may be found in the center of the
tuber as well (van der Zaag, 1996).
The vascular necrosis in tubers associated
with low-temperature injury may resemble that
14.14
Low-Temperature Injury
Low-temperature injury ranges from slight dam-
age caused by exposure to non-freezing temper-
atures to outright freezing and death of tuber
tissues. Low-temperature injury may occur in
the field, during storage, or in transit. Synonyms
for low-temperature injury are freezing necrosis,
freezing injury, frost necrosis, frost injury, chilling
injury, and mahogany browning. The severity of
low-temperature injury depends on tempera-
ture, length of exposure, and cultivar. Within
any lot of tubers, at a given temperature, the de-
gree of tissue damage and the range of injuries
found may vary considerably.
Ice crystals form in the tissues of tubers
exposed to freezing temperatures, causing irre-
versible damage. Potato tissues freeze at temper-
atures of -1.9°C to -1.4°C, and when exposed
to temperatures at or below -2.8°C, extensive
mortality occurs (Boydston et al ., 2006).
Damage due to prolonged freezing or very low
 
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