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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Biological Control 233
In fact, postharvest decay control in pear fruits by the yeasts,
Rhodotorula and Cryptococcus has been demonstrated following both
field sprays (Benbow and Sugar, 1999) and postharvest application
(Chand-Goyal and Spotts, 1996a). Similarly, the efficiency of yeasts of
the genera Pichia and Hanseniaspora in controlling Rhizopus and
Botrytis decay in grapes has been expressed following both sprays in the
vineyard prior to harvest, and dipping of harvested fruit in the
antagonist yeast cell suspension (Ben Arie et al., 1991).
C. MODE OF ACTION OF THE ANTAGONIST
Elucidation of the mechanisms by which antagonists inhibit
postharvest pathogens is important for the development of a more
reliable procedure for the effective application of known antagonists and
for providing a rationale for the selection of more effective antagonists
(Wilson and Wisniewski, 1989). Several modes of action have been
suggested to explain the biocontrol activity of antagonistic microorganisms
(Droby et al., 1992; Droby and Chalutz, 1994; Wilson et al., 1994):
(a) the secretion of antibiotic compounds;
(b) competition for nutrients at the wound site;
(c) direct effect of the antagonist or enzymes secreted
by it, on the pathogen;
(d) induction of host defense mechanisms.
(a) The secretion of antibiotic compounds by the antagonist.
Examples of microorganisms which inhibit the pathogen via the
production of antibiotics are the bacteria. Bacillus subtilis and
Pseudomonas cepacia. The early study of Gutter and Littauer (1953 )
found B, subtilis able to inhibit the development in culture of the main
pathogens of harvested citrus fruits. More than 30 years later, it was
found that this antagonist was effective against fungal development in
citrus fruit (Singh and Deverall, 1984) and against Monilinia fructicola
in peaches and cherries (Pusey and Wilson, 1984; Utkhede and Sholberg,
1986). Analytical tests of the antibiotic substance secreted by an active
isolate of B. subtilis indicated the presence of iturins, which are cyclic
peptides made of seven a acids and one p acid. They are characterized by
a wide antifungal spectrum including fungi pathogenic to man and
plants (Pusey, 1991; Gueldner et al., 1988). It is interesting to note that
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