| Tuber
Internal Growth Defects: FREEZING
Freeze
injury to tubers can occur in the field, in storage or in transit
due to exposure to below freezing temperatures, <30oF. In storage
of seed and table stock tubers, freezing is usually associated with
poor ventilation and poor insulation.
External
Appearance:
Prior
to thawing, affected tuber area is hard. After thawing, affected
tuber area appears wrinkly and flabby. It may have a "weeping"
effect, that is, water will leak from tuber surface.
Diagnostic
Method:
Cut
through affected area.
Internal
Appearance:
Although
seemingly similar to chilling, the underlying tissue will be bluish-grayish
and the margin will be sharply defined, not diffuse. Also, unlike
chilling, there will not be a net necrosis. Upon thawing, affected
tissue will gradually change from a dull, off-white (grayish) color
to pinkish-reddish to brown-black. The tissue breaks down from being
hard (frozen) to a watery texture, soft and wet.
Cooking
Appearance:
Not
suitable for table stock or processing. Tissue breaks down during
cooking, such as sloughing during boiling and becoming a watery
mush during baking. May be used for dehydration.
Development:
Ice
crystals form in cells upon freezing. These puncture the cell and
organelle membranes. Upon thawing, the cells loose structural integrity
and spill out their contents. Bacterial soft rot commonly will attack
thawed affected tissue in storage. Don't use for seed due to poor
sprouting and high susceptibility to soft rot.
Control
Measures:
Avoid
exposure to temperatures below 30oF. If freeze occurred in the field,
discard affected tubers; don't store them. Don't mix tubers from
fields exposed to a freeze (tend to get soft rot) with those that
weren't.
- Harvest
before soil temperature drops to freezing.
- Tarp
truckloads.
- Don't
store against an outside wall.
Summary:
Internal Disorders |
