Tuber Physiological Disorders - The Potato: Botany, Production and Uses - page 243

areas around the eyes and on the periderm of tis-
sues between the eyes, initially on the bud end of
the tuber. As the disorder progresses, water-
soaked or dried and cracked corky patches de-
velop on the tuber (Sabba et al ., 2008). The corky
patches develop late in the season or during stor-
age and are known as “corky patch syndrome”
or “bull hide” (Secor and Rouse, 1992). The
thickened corky patches may extend up to 3 mm
into the tuber flesh (Nolte et al ., 1993). Internal
symptoms of pink eye progress from erratic
browning of cortical cell walls to necrotic zones,
often surrounded by an internal, pink eye-related
periderm (Sabba et al ., 2008). On exposure to
ultraviolet light, tissues directly beneath the
areas affected by pink eye exhibit intense autoflu-
oresence (Nolte et al ., 1993), due to the presence
of suberin poly(phenolic(s)) (Lulai et al ., 2006).
Pink eye has been implicated as a precursor
to many tuber diseases such as bud end decay
(Secor and Rouse, 1992). Suberized cells of the
native periderm of pink eye surfaces are com-
promised or deteriorated, increasing tuber sus-
ceptibility to rot organisms (Lulai et al ., 2006). It
is hypothesized that very wet and hot soil condi-
tions contribute to low oxygen levels in the soil,
resulting in cell damage and death in the tuber
periderm and underlying cortical cells, and the
development of pink eye (Sabba et al ., 2008).
Pink eye is associated with excessive mois-
ture late in the season in conjunction with high
soil and air temperatures (Secor and Rouse,
1992; Copas et al ., 2008). Pink eye is most severe
after periods of saturated soil conditions or pro-
longed periods of free water followed by high
temperatures. Copas et al . (2008) found pink rot
symptoms appeared 7- 10 days after excessive ir-
rigation or precipitation events. Tubers from
fields with a long history of potato production
tend to develop pink eye (Secor and Rouse, 1992).
Control of pink eye is difficult. Avoid exces-
sive moisture prior to and during tuber harvest.
There is no control in storage, but it is important
to provide cool, dry conditions to prevent the
development of soft rot.

heart are considered to be two different phases
of the same internal disorder, and are likely in-
duced by similar conditions. Brown center and
hollow heart, although related, can occur
independently of each other. Brown center is
believed to be a precursor to hollow heart, al-
though hollow heart does not always develop
(Hiller et al ., 1985). Affected tubers and plants
show no external symptoms.
Brown center is a small, firm, brown dis-
coloration of pith tissue near the center of the
tuber. Tubers are most susceptible to brown
center when they are very small, from the
tuber initiation stage up to the time when
tubers weigh 56 g (Thornton, 2001b). The dis-
coloration arises from damage to cell mem-
branes and organelles, and necrosis of affected
cells (Van Denburgh et al ., 1986). Cool soil
temperatures, for example 10- 15°C, around
the time of tuber initiation are reported to in-
duce brown center (Hiller et al ., 1979; Van
Denburgh et al ., 1980). Damage to pith cell
membranes begins to appear after 5 days at soil
temperatures of 10°C, with brown center
visible to the naked eye after 16 days (Van
Denburgh et al ., 1986). High soil moisture in-
creases the severity of brown center (Hiller and
Koller, 1981). If tuber growth is slow and uni-
form after discoloration develops, growth of
living cells spreads and disperses the dead
ones, dissipating the brown color by the end of
the growing season (Thornton, 2001b).
If, however, the tuber grows rapidly, the
affected tissues may tear or split apart and
form a cavity due to growth of the perimedul-
lary region of the tuber outpacing that of the
pith region (Rex and Mazza, 1989). The result
is the disorder known as hollow heart. In the
past, the only way to detect hollow heart was
to cut the tuber open. Equipment that detects
hollow heart via X-rays is commercially avail-
able and in use in North America. Other
non-destructive means of detecting hollow
heart that have been studied include acoustic
impact (Elbatawi, 2008), ultrasonics (Jivanu-
wong, 1998), and nuclear magnetic resonance
imaging (Wang et al ., 1997).
Hollow heart refers to a cavity in the cen-
tral pith of a potato ( Fig. 14.3 ). It may be lens-,
star-, or irregularly shaped, and range in size
from a small gap of a few millimeters long to a
hole that occupies almost the entire tuber pith

14.9 Brown Center
and Hollow Heart

Brown center (also known as incipient hollow
heart, brown heart, or sugar center) and hollow