Post harvest diseases fruits and vegetables - Xavier University ...

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
86 Postharvest Diseases of Fruits and Vegetables
temperatures, which do not promote suberin formation by the cells
surrounding the wound, facilitates the development of gangrene caused
by Phoma infection in stored potatoes. This is because temperatures
which prevent the formation of suberinic barriers by the host are still
suitable for the development of the fungus (Boyd, 1972).
Suberin also serves as a defensive layer on the lenticels of potato
tubers. Lenticels of potatoes are normally covered with a suberin layer
that prevents the entry of soft rot bacteria into the cortex of the tuber.
Removal of this layer renders the lenticels susceptible to bacterial
invasion (Fox et al., 1971; Perombelon and Lowe, 1975).
Kolattukudy (1987) described suberin as a complex biopolyester
comprising a phenolic (aromatic or lignin-like) domain attached to the
cell wall, and an aliphatic (lipid, hydrophobic) domain, which is probably
attached to the phenolic domain. Soluble waxes are imbedded within the
suberin matrix and provide resistance to water vapor loss but have not
been indicated to play a role in disease resistance (Lulai and Corsini,
1998). However, rapid suberization of wounded tubers is critical in
avoiding both bacterial soft rot (Erwinia carotovora subsp. carotovora)
and fungal dry rot (F.. sambucinum). Lulai and Corsini (1998)
emphasized the differential development of potato tuber resistance to
bacteria and then to fungal penetration during suberization. They
related this phenomenon to the differential deposition of the two major
suberin components (the phenolic and the aliphatic domains) during
wound healing (18°C at 98% RH). It was found that the initiation of
suberin phenolic deposition at the wound site preceded that of suberin
aliphatic deposition. Total resistance to Erwinia infection occurred after
completion of the phenolic deposition on the outer wall of the first layer
of cells (2-3 days). However, the phenolic suberin deposition offered no
resistance to Fusarium infection. Resistance to fungal infection began to
develop only after deposition of the suberin aliphatic domain was
initiated. Total resistance to fungal infection was attained after
completion of deposition of the suberin aliphatic domain within the first
layer of suberized cells (5-7 days). This suberin domain was not required
for tuber resistance to bacterial soft rot infection.
Curing sweet potatoes for several days at high relative humidity
(85-90%) and high temperatures (26-32°C) facilitates the formation of
suberized periderm, which protects harvest injuries against attack by
Rhizopus stolonifer (Clark, 1992). In fact, curing is a standard prestorage
treatment to prevent decay in various varieties of sweet potatoes.
Similarly, holding carrots at high relative humidity and 22-26°C for 2
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