| Tuber
External Growth Defects: HAIR SPROUTING
Premature
sprouting of tubers late in the season or early in storage affects
quality of the harvested tubers. Besides appearance, the sprouts
soften the tuber by taking up its nutrients and lowering the starch
content. The taste of the tuber is uneven with a sweeter taste near
the sprout. This makes the tuber unacceptable for processing since
frying will turn this area dark.
Development
and Appearance
Sprouts
appear from the eyes of the primary tuber. The hair sprout is very
thin, hair-like, and is too weak to emerge or grow much. A related
to hair sprouting is heat sprouting which may remain underground,
or emerge and become green and leafy. Tuber sprouting is a hormonal
phenomenon involving the lack of development of tuber dormancy,
related to abscissic acid (ABA).
Causation
The
cause of heat and hair sprouting is high soil temperature. The conditions
for this disorder are similar to that for tuber chaining (see above)
except that exposure to high soil temperature is toward the end
of the growing season, late bulking or plateau stages (Potato Production
Stages: Scheduling Key Practices, Univ. Nebr. Coop. Ext. Circ. #
95-1249). Once sprouted, the sprouts will grow under good conditions.
In other words, tuber dormancy does not develop. Hair sprouting
is also a symptom of infection with Colletotrichum atramentarium,
related to black dot, and associated with aster yellow carried by
leafhoppers and psyllid yellow carried by potato/tomato psyllids.
Susceptibility
Varieties,
in general, are susceptible but varieties with short tuber dormancy
periods may be more so.
Cultural
Practices
Practices
to minimize this disorder are the same as for tuber chaining. Since
air temperature cannot be controlled, the best practices to avoid
over-heating of the soil are to plant deep, to hill and to maintain
a good row structure. In severe hot weather, cooling the ground
with irrigation may be necessary.
Summary:
External Disorders |
