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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Physiological and Biochemical Changes 103
The origin of PG in Rhizopus stolonifer-miected tomatoes has been
studied in various tomato fruits (Barkai-Golan et al., 1986): (a) a non
ripening nor tomato mutant, which contains no PG during any stages
of development; (b) a green normal fruit, which does not contain PG
while still unripe; and (c) a ripe red fruit, which contained PG of plant
origin. Analysis by gel electrophoresis of Rhizopus PG, after in vitro
growth, revealed the production of at least seven molecular forms of this
enzyme. In each of the fruits tested, Rhizopus infection resulted in the
accumulation of these typical PG isozymes, which are all of fungal
origin; however, in the infected ripe tomato fruit, both fruit and fungal
enzymes were found. An analysis by gel electrophoresis enabled
differentiation between the isozyme bands of the tomato and those of
the fungus which migrated in the gel faster than those of the fruit PG.
It could not, however, provide a clear differentiation between the
slower-migrating fungal isozymes and the fruit isozymes (Barkai-Golan
et al., 1986). The differentiation between these isozymes was completed
by immunological analysis with antiserum against specific forms of
tomato enzymes; this analysis demonstrated that the infected fruit
contained a higher level of tomato enzyme than the uninfected fruit of
similar maturity. It was concluded that infection by R, stolonifer
enhanced PG production in the normally ripening fruit or, in other
words, that the infection advanced the ripening process in genetically
competent tomato tissue. The infection did not, however, induce PG in
the non-ripening nor fruits, which lack an active ripening system and
are unable to produce PG naturally (Barkai-Golan et al., 1986).
Clarification of the origin of PG in the infected tissue also suggests that
the pectolytic enzymes of the mature tomato fruit can take an active
part in fungal pathogenicity or contribute to disease development.
D. STIMULATION OF FRUIT SOFTENING AND CHANGES
IN THE PECTIC COMPOUND CONTENTS
Examination of avocado fruits infected by Fusarium solani has
revealed that their softening starts earlier than in uninfected fruits, and
that it occurs during the incubation period of the pathogen, before the
appearance of decay symptoms (Zauberman and Schiffmann-Nadel,
1974). Furthermore, softening does not begin at the point of infection
and progress outwards from there, but occurs simultaneously in the
whole fruit. This finding raised the suggestion that the advance in fruit
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