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

more heavily in the vascular region. Cold-induced net necrosis is
very similar in appearance to virus leafroll net necrosis.
Following severe injury, blackish patches or blotches may
develop near the vascular ring, which may also be partially or
completely blackened (Fig. 7C and D). Injury is usually more
severe near the stolon end.
Internal mahogany browning (Plate 2) is a different low
temperature response, in which diffuse brownish red to black
discoloration ispresent, usually in the central part ofthe tuber.
This disorder grades into blackheart. Shrinkage in affected
tissue results in cavities. Blackheart and probably internal
mahogany browning result primarily from asphyxiation of
internal tuber tissue.
Epidemiology
Individual tubers from the same lot vary considerably in
response to a given temperature. Immature tubers are
frequently more severely injured.
Biecaiuse of hardening or acclinmatizatior, tubers that have
been drop stored in temperature
at low temperatures are less
than
injured by a sudden
are those stored at higher
temperatures.
.ow temperatures fra few hours or temperaturesjust below
free/ing for a short freeingfor time tme call an shrt lower owerintrnalquaityshoten
internal quality, shorten
storage life, and impair storge suitability ifeuitailiy andimpir of' o the thetubr tuber for fr processing prcesing
without leaving visible evidence. Tu,bers may be supercooled to
approximately -3.0 C. and even to -6.5' C for a,few hours,
without ice crystal formation and, if gradually warmed, do not
havc evident injury. However, jolting or jarring supercooled
tubers will cause intracellular ice crystals to form and cells to
die. Storage at low temperatures, even in the absence of
symptoms, impairs the tuber's ability to form wound barriers
when returned to favorable temperatures. Injured seed tubers
with or without symptoms sprout poorly and may fail to
produce plants because of secondary seed piece rots.
Alternating temperatures during the storage season avoids
chilling injury and its associated problems. Tubers held
alternately for three weeks at 0' C and one week at 16' C had a
lowered content of reducing sugars (as well as of total sugars),
reduced respiration rates, and no low temperature injury,
whereas at constant O°C tuber injuries became progressively
more severe after eight weeks in storage.
Control
I) Field-frosted tubers should not be moved into storage if at
all possible.
2) Hold storage temperatures at 3.5-4.51C, which is
sufficiently high to prevent low temperature injury.
3) Maintaia adequate air movement in stored potatoes to dry
frost-injured tubers and provide adequate oxygen for
respiration.
4) Tubers injured by low temperatures or suboxidation
should not be used for seed.
5) Certain cultivars are more prone to mahogany browning
than are others. Varietal differences with respect to other
aspects of low temperature injury are not so pronounced.
Selected References
CUNNINGHAM. H1.IL.. M. V. ZAEH RINGER, G. BRAUSEN. and
W. C. SPARKS. 1976. Internal quality' of Russet Burbank
potatoes following chilling. Am. Potato .1.53:177-187.
tR USCH KA, II. W.. W. I.. SM I If..r., and .1. E. BAKER. 1969.
Reducing chilling injury of potatoes by intermittent warming. Am.
Potato .1.46:38-53.
.JONES. .. R., M. MII.L.ER. and 1. BAILEY. 1910. Frost necrosis of
potato tubers. Wis. Agric. Exp. Sin. Res. Bull. 46. 46 pp.
LINK. G. K. K.. and G. 1B.RAMSEY. 1932. Market diseases of fruits
and vegetables. Potatoes. U.S. Dept. Agric. Misc. Publ. 98. 62 pp.
RICHARDSON. L.T.,and W. R. PiIII.I.IPS. 1949. I.ow temperature
breakdown of potatoes in storage. Sci. Agric. 29:149-166.
(Prepared by W. J. Hooker)
Low Temperature Foliage Injury
Certain symptoms of nonlethal low temperature foliage
injury may be confused with virus symptoms or herbicide
damage. Lethal freezing of leaves and stems isreadily identified.
Symptoms
Frozen leaves rapidly wilt, collapse. and when thawed,
become water-soaked. They turn black when damp and brown
when dried. Less severe low temperature injury, usually
occurring in the early to middle part of the growing season,
often produces a buff to light brown or yellow discoloration on
the top of the plant and particularly at the bases of young
leaflets.
Temperatures at or near 0' C selectively injure leaf and stem
primordia and possiblycell organelles. Symptoms ofthis injury
become evident after leaflet expansion as unilateral leaflet
development, irregular distortion of leaflets, or grayish
transverse banding accompanied by restricted lateral expansion
(Fig. 8).
Chlorosis in diffused areas, in spots, or in portions of veins
nay be seen and mottle patterns may be present with or without
leaf Necrotic distortion specks following may develop nonlethal on young low leaves temperatures following (Plate -0.3° 3). C
wet Nertcsckmadvlooiyunlaesflwng-.0
bulb temperatures. Injury of this type appears after leaves
from damaged primordia have expanded. Normal growth may
precede and should follow these low-temperature effects, but
symptoms on injured parts persist.
Epidemiology
Low temperature injury is usually most severe in low-lying
areas of fields. At high elevations and latitudes, freezing may
occur at any time in the growing season.
Because leaf surfaces are frequently well hydrated and often
wet with dew, wet bulb temperatures should be more reliable
than dry bulb temperatures in determining critical temperatures
for leaf injury.
Plants on which some leaves have been frozen recover from
injury slowly, suggesting more damage than that of the tissue
actually destroyed. Growth retardation may be due to
resorption of tissue degradation products.
Solarim acauk,, its derivatives, and approximately 10 more
wild potato species, as well as several cultivated clones
Fig. 8. Leaf deformation following low temperature injury of leaf
primordia.
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