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

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Physiological and Biochemical Changes 105
E. CHANGES IN BIOCHEMICAL CONSTITUENTS OF
INFECTED TISSUES
In various host/pathogen systems, fruit infection results in the
decrease or total disappearance of the sugar content of the fruit. Such
systems include: lemon fruits infected by Phytophthora citrophthora
(Cohen and Schiffmann-Nadel, 1972); pineapples infected by Ceratocystis
paradoxa (Adisa, 1985a); other tropical fruits, such as guava, papaya and
banana, infected by various pathogens (Ghosh et al., 1964; Odebode and
Sansui, 1996); watermelons infected by Alternaria cucumerina strains
(Chopra et al., 1974); and cucumbers infected by Pythium
aphanidermatum (McCombs and Winstead, 1964). This common
phenomenon has generally been related to the stimulation of respiration
in the infected tissue. An interesting phenomenon was recorded in
banana fruits: whereas the presence of glucose, sucrose, fructose, maltose
and raffinose were recorded in healthy fruits, only sucrose appeared
during storage of bananas infected with Botryodiplodia theobromae
(Odebode and Sansui, 1996). On the other hand, inoculation of
pineapples with the fungus Curvularia verruculosa resulted in an
increased level of sugars, probably because of the activity of
cell-wall-degrading enzymes of the fungus (Adisa, 1985a).
Inoculation of citrus fruits with Penicillium digitatum considerably
affected the D-galacturonic acid content of the peel (Achilea et al.,
1985a). During the infection process the fungus produces
exo-polygalacturonase, which hydrolyzes the cell wall pectin into
monomers of galacturonic acid (Barmore and Brown, 1979), which is
responsible for cell disintegration and tissue maceration.
Fungal infection may result in the reduction of the organic acid level.
Reductions in ascorbic acid were recorded in lemons infected by
Phytophthora citrophthora, in bananas infected by various storage
pathogens, and in chili fruits infected by Colletotrichum gloeosporioides
(Cohen and Schiffmann-Nadel, 1972; Khodke and Gahukar, 1995;
Odebode and Sansui, 1996). The absence of citric acid from pineapples
was recorded in fruit infected by Ceratocystis and Curvularia (Adisa,
1985a). It has been suggested that the pathogenic fungi might use
organic acids for their respiration, thus leading to their decreased level
or disappearance from the tissue.
Several cases have been reported of changes in the protein level in the
plant tissue during disease development: a reduction in the protein
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