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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
226 Postharvest Diseases of Fruits and Vegetables
variability of A pullulans, by obtaining 41 isolates from the surfaces of
fruits and vegetables cultivated in Italy. They found that only a few
isolates had the same genetic patterns and showed similar biocontrol
activities.
Research in the past decade has mainly focused on microorganisms
that are antagonistic to 'wound pathogens'. Since infection of wounds by
fungal spores is very rapid, rapid colonization and growth at the wound
site is a key characteristic of a successful antagonist (Droby et al., 1996).
The features required for effective biocontrol agents should, therefore,
include: the ability of the antagonist to colonize wounds; a rapid rate of
growth in surface wounds; effective utilization of the nutrients present in
the wound; and the capability to survive and develop at the infection
sites better than the pathogen and to do so under a wider range of
temperature, pH and osmotic conditions (Droby et al., 1996).
An important point in the selection of biological control antagonists is
the necessity to avoid strains or isolates that may injure either the
plants they are intended to protect or other plants of economic
importance. Hence, screening tests to prevent the use of harmful
microorganisms should be a part of any effort to develop biocontrol
antagonists (Smilanick et al., 1996). Pseudomonas syringae strains, for
instance, can occupy wounds on the peel of citrus fruit and reduce the
incidence of postharvest rots initiated by wound pathogens. However,
some P. syringae pv. syringae strains are pathogens of citrus and other
plants and, therefore, strains should not be approved for biological
control until their risk of virulence to many hosts has been determined
(Smilanick et al., 1996).
B. INTRODUCTION OF ANTAGONISTS FOR DISEASE
CONTROL
To identify antagonists as promising agents, a screening system
should simulate natural inoculation, and the inoculum should be applied
in the proper infection courts at the proper time (Smilanick, 1994). The
selection of the inoculation method used for in vivo screening is,
therefore, critical to a successful strategy. A biocontrol agent has
generally been introduced to the wound site prior to the arrival of the
pathogen or shortly thereafter (Smilanick, 1994). Applying the
antagonists after inoculation of the pathogen involves eradicative action.
The synthetic fungicide imazalil, for instance, controlled green mold
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