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.


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:

  1. Irrigate to maintain uniform growth. Use evapotranspiration (ET) or monitor soil moisture to schedule irrigation.
  2. Allow gradual vine desiccation.
  3. Irrigate somewhat after vine kill.
  4. 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.
  5. Avoid highly salinated (sodium) fields especially with high levels of residual nitrogen. Avoid over fertilization with nitrogen.
  6. Avoid tillage practices that compact soil. Last cultivation should be before emergence and first irrigation should be after emergence.