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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
68 Postharvest Diseases of Fruits and Vegetables
PG-inhibiting protein from pears, a step that may lead to the expression
of inhibitory proteins in transgenic plants and contribute to the
inhibition of decay development. Following the finding that ripening
tomato fruits from transgenic plants expressing the pear inhibitory
protein gene were more resistant to B. cinerea infection than the control
fruits (Powell et al., 1994), PG-inhibiting proteins have been considered
as pathogen infection resistance factors.
A PG-inhibiting protein purified from mature apple fruits (Yao et al.,
1995) showed differential inhibitory activity against five PG isozymes
purified from B, cinerea grown in liquid culture. However, inhibition was
not detected against PG extracted from apple fruits inoculated with the
same fungus; in contrast to the several isozymes isolated from fungal
culture, only one PG was isolated from apple fruits inoculated with B.
cinerea. The absence of multiple PG isozymes in inoculated fruits may
suggest that the PG-inhibiting protein is involved in limiting the
production of most PG isozymes during fungal infection. In other words,
although the apple fruits did not show inhibitory activity against the PG
isozyme isolated from inoculated fruits when assayed in vitro, this does
not exclude the possibility that an apple inhibitor may contribute to the
general resistance mechanism of the fruit when fighting fungal infection.
Its application has even been considered as a possible alternative method
for controlling postharvest diseases (Yao et al., 1995). A new protein
inhibitor that may be involved in the inhibition of enzymes necessary for
microbial development was isolated from cabbages (Lorito et al., 1994); it
significantly inhibited the growth of B. cinerea by blocking chitin
synthesis, so causing cytoplasmic leakage. Several studies supported the
theory that natural protein compounds within the plant tissue may act
as inhibitors of pathogen enzymes, and that these inhibitors may be
responsible for the low levels of PG and PL found in infected tissue
(Fielding, 1981; Barmore and Nguyen, 1985; Bugbee, 1993).
Recent studies show a close correlation between the changes in the
level of epicatechin in the peel of avocado fruits and the inhibition of
pectolytic enzyme activity of Colletotrichum gloeosporioides. The
epicatechin was found in unripe fruits at concentrations much higher
than those required for in vitro inhibition of purified PG and pectate
lyase (PL) produced by the fungus (Wattad et al., 1994). This led to the
suggestion that epicatechin may contribute to the quiescence of the
fungus by inhibiting the activity of pathogenicity factors. The importance
of pectate lyase as a pathogenicity factor during the activation of
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