Compendium of Potato Diseases - (PDF, 101 mb) - USAID

Internal Sprouting multiple sprouts also cause internal sprouting.
Sprouts that develop during storage may become ingrown by
penetrating into the tuber. Internal sprouts frequently are in
eyes with tightly clustered multiple "rosette" sprouts, which may
be unbranched or. more frequently, nranched (Fig. 20). Sprouts
may penctratCtile tuber directly above. or sprouts from an eye
on the bottom of the tuber may grow up through the same tuber.
Sprouts from tubers ssith deep eyes may penetrate into tile side
of the eve depression.
The disorder has been kno\n for oser a century. It is more
frequent in old tubers and in those stored at 12-15 ° C. Pressure
on tubers within the storage pile restricts sprout growth and
induces sprout penetration of tuber tissue. In old tubers, sprouts
often tuberi/e within the parent tuber, splitting it open.
Internal sprouting was recently associated with sprout
inhibitors used in concentrations below those required for
complete sprout inhibition. Concentrations that completely
inhibit all external sprouts also inhibit internal sprouts, but
insufficient concentrations actually stimulate internal sprouts.
Isopropyl-nm-chlorocarbanilate (CI PC) stimulates internal
sprouting to agreaterextent than does pressure on tubers under
a deep pile. Other chemicals stimulating tightly clustered,
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"
Fig. 20. Internal sprouting, showing rosette of sprouts on the
underside, small tubers on internal sprouts, and necrosis under
or at the sprout apices. The last resembles calcium deficiency.
(Courtesy E. E.Ewing)
r
-'"Coiling
Fig. 21. Secondary tubers formed directly on sprouts from
physiologically old tubers.
Necrosis at or slightly below the sprout apex is common on
the external sprouts of tubers containing internal sprouts, and
apicies of internal sprouts become similarly necrotic when they
emerge from the tuber. (See Ca deficiency.)
Selected References
EWING. E. E...1. W. LAYER. .1.C. IIOHN, and 1). J. I.ISK. 1968.
Effects of chemical sprout inhibitors and storage conditions on
WIEN, internal II.C.and sprouting 0. SMITH. in potatoes. 1969. Am. Influenceof Potato .1.45:56-71. sprout tip necrosisand
rosette sprout formation on internal sprouting of potatoes. Am.
Potato .1.46:29-37.
(Prepared by W. J. Hooker)
Secondary Tubers
Tubers sprout either in storage or in the field, producing tiew
tubers directly without forming a normal plant. Secondary
tubers form on sprouts from physiologically old tubers after
completion of the rest period when carbohydrate reserves are
low (Fig. 21). The disorder is associated with warm (200C)
storage followed by low temperature after planting or by
transfer of sprouted tubers from warm to cold storage. Even at
low temperatures, however, physiologically overmature tubers
held past normal usage form secondary tubers. Usually the
problem is of minor importance, although poor field stands with
missing hills result. (See also calcium deficiency.)
Selected References
BURTON, W.G.1972. The response of the potato plant and tuber to
temperature. Pages 217 -223 in: A. R. Rees. K. F. Cockshull. I). W.
Hand, and R. G. [lurd. cos. Crop Processes in Controlled
Environinents. Academic Press. Ness York. 391. pp.
DAVIDSON, T. M. 1958. t)ormancy in the potato tuber and the effects
of storage conditions on initial sprouting and on subsequent sprout
growth. Am. Potato J. 35:451-465.
VAN SCHREVEN, I). A. 1956. On the physiology of tuber formation
in potatoes. 1. Premature tuber formation. Plant Soil 8:49-55.
(Prepared by W..1. Hooker)
Coiled Sprout
The disease has been reported primarily from the British Isles,
where up to 26% of plants in certain fields are affected, but it
probably exists elsewhere.
Symptoms
Underground sprouts lose their normal negative geotropic
habit and coil. sometimes rather tightly, with the curved portion
of the stem often swollen and sometimes fasciated or split (Fig.
22). Light brown lesions with transverse or longitudinal cracks
may be present on the stem inside the coil. Delay in emergence of
coiled sprouts results in uneven stands. Affected plants may
produce more stems than normal, and tubers may form
unusually early and mature slowly.
Causal Factors
is believed to be the result of overmature seed, soils
resistant to sprout penetration and emergence, or infection by a
fungus. Verticillium nuhilunt Pethybridge has been isolated
from affected stems. This pathogen has caused superficial
browning and russeting of some stem bases, accompanied by
shallow cortical invasion underlaid by suberin. In some
instances, inoculation with the pathogen has caused coiled
sprout, but IVnubihmn is not the sole cause of the disease.
Low soil temperatures. presprouting in light, long sprouts at
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