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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
106 Postharvest Diseases of Fruits and Vegetables
content along with an increase in the free amino acids. However, in other
cases infection had no effect on the protein content of the tissue, or even
resulted in their increase (Adisa, 1985a; Khodke and Gahukar, 1995).
Several amino acids, such as histidine, arginine, aspartic acid, glycine,
alanine and leucine, increased in infected fruits, whereas the levels of
lysine, threonine, glutamic acid, proline, cystein, valine, methionine and
others all decreased following infection (Khodke and Gahukar, 1995).
Polyamines, which are responsible for the control of nucleic acid
synthesis and function (Slogum et al., 1984), play an important role in
plant growth and development (Galston, 1983). The relationship between
disease development and polyamine content in the fruit has been studied
in Rhizopus stolonifer-infected tomato fruits (Bakanashvili et al., 1987).
Marked reductions in the activities of the enzymes ornithine
decarboxylase and arginine decarboxylase were recorded in the healthy
tomato fruit during fruit development and towards ripening, but, as a
result of the changes in the activities of these enzymes, the content of the
polyamine putrescine, as well as those of the polyamines permidine and
spermine which derive from it, were markedly reduced, and reached
their lowest levels during ripening (Bakanashvili et al., 1987).
Inoculation of preclimacteric tomato fruits with R, stolonifer was found
to induce, in addition to fruit ripening, a reduction in the activity of the
enzymes ornithine and arginine decarboxylase and, consequently, to
reduce the polyamine level in the fruit. Since treatment with exogenic
ethylene elicited phenomena similar to those associated with fungal
infection or fruit ripening, it has been suggested that the ethylene
induced by pathogen infection may be responsible for the altered
polyamine content of the Rhizopus-iioSected tomato fruits.
Numerous biochemical changes occurred in potato tubers inoculated
with Fusarium sambucinum, the causal agent of dry rot in stored tubers
(Ray and Hammerschmidt, 1998). Peroxidase activity, which is very low
in the uninfected tuber, increased up to 500-fold after inoculation with
the fungus. High levels were recorded in tissue just ahead of the
advancing hyphae. Smaller increases were recorded in tubers following
wounding alone. Lignin content increased in tubers following inoculation,
the highest concentrations being detected 40 h after inoculation, when
the infected surface was often partly or entirely decayed. As disease
progressed, the lignified zone increased in depth until it comprised five or
six cell layers. Here again, responses to F. sambucinum infection were
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