| Tuber
Internal Growth Defects: JELLY END & GLASSY END
The
terms jelly, translucent, glassy and sugar end all refer to various
characteristics of the same disorder. This disorder is most associated
with water deficit in plants due to low soil temperature, high air
temperature, dry winds, and too much top growth with respect to
tuber growth. It may occur early in the season around tuber initiation
or late in the season near harvest. It may be associated with too
rapid vine desiccation.
External
Appearance:
The
stem end tends to be pointy and is also associated with a dumbbell
tuber shape. Jelly end describes the flaccidity, wiggliness, of
the stem end. Upon drying, the stem end becomes leathery and shrivels;
the skin becoming wrinkled.
Diagnostic
Method:
Cut
longitudinally from stem end to about two inches, and expose the
cut surface.
Internal
Appearance:
The
tissue at the stem end will have a glassy or opaque appearance hence
the term glassy or translucent end. The affected area is sharply
bordered from healthy tissue and usually extends less than two inches
into the tuber.
Cooking
Appearance:
Upon
frying, the stem end turns brown to black because of its high sugar
content; therefore the terms sugar end or stem-end discoloration
(SED). This is primarily a problem in french fry processing and
Russet Burbanks are especially susceptible. Chips from the stem
end are dark and unusable. After boiling or baking, stem end remains
opaque.
Development:
Inadequate
soil moisture during early bulking coupled with high temperature
seems to cause this disorder. Jelly end appears due to a lack of
starch at the stem end resulting in a low specific gravity. Reducing
sugars like glucose are high. The disorder is most prevalent in
pointy and dumbbell-shaped tubers and in long tuber shaped varieties
as Russet Burbank. Two general causal theories have been proposed.
Starch breakdown or removal from the stem end when growth renews
after stress. And, starch produced in the leaves is either not broken
down and transported to tubers or, in tubers, the starch breakdown
product is not reassembled into starch for some reason.
Control
Measures:
- Irrigate
to maintain uniform growth. Use evapotranspiration (ET) or monitor
soil moisture to schedule irrigation.
- Allow
gradual vine desiccation.
- Irrigate
somewhat after vine kill.
- Don't
plant after sugar beets because of low crop residue and compaction.
Planting after corn or small grains is preferred with shallow
incorporation of residue for good soil aeration and water infiltration.
- Avoid
highly salinated (sodium) fields especially with high levels of
residual nitrogen. Avoid over fertilization with nitrogen.
- Avoid
tillage practices that compact soil. Last cultivation should be
before emergence and first irrigation should be after emergence.
Summary:
Internal Disorders |
