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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
242 Postharvest Diseases of Fruits and Vegetables
fungal growth (Schlumbaum et al., 1986), while peroxidases are involved
in the formation of structural barriers against pathogen invasion (El
Ghaouth et al., 1998). A. pullulans could thus induce further decay
control through a multiple-component mode of action against the
pathogen (Ippolito et al., 2000).
D. ANTAGONIST MIXTURES TO IMPROVE DISEASE
BIOCONTROL
The development of biological control has made much progress during
the last decade. Today, with several biocontrol treatments approved for
commercial application and others undergoing the approval process,
research is being focused on improving both the antagonist efficacy and
the control system. One of the approaches to improving biocontrol agents
is by selecting combinations of antagonists that will act better than each
of the components separately.
A combination of the bacterium Pseudomonas syringae and the pink
yeast Sporobolomyces roseus proved to have a marked advantage over
each of the antagonists in controlling Penicillium expansum in apples,
both in reducing the incidence of wound infections and in limiting rot
diameter (Janisiewicz and Bors, 1995). After application of the mixtures,
populations of S. roseus in the wounds were found to be consistently
lower than those after individual applications, whereas populations of
P. syringae were not affected by the presence of the other antagonist.
When 35 nitrogen sources were tested for utilization by the antagonists,
both S. roseus and P. syringae were found to utilize 14 sources, whereas
P. syringae utilized an additional nine compounds. On the other hand,
more carbon sources were utilized by S. roseus than by P. syringae. It
was concluded that the populations of the antagonists in apple wounds
form a stable community, dominated by P. syringae. This domination was
attributed to the ability of P. syringae to use nitrogen sources, which
form the limiting factor in the carbon-rich apple wounds. This is an
example of the possibility of exploiting the differing nutritional features
of the antagonists to achieve improved biological control at the wound
site.
In a further study, Janisiewicz (1996) reported on the development of
antagonist mixtures that were superior to individual antagonists in
controlling blue mold (P. expansum) of apples; the development was
based on ecological knowledge of the distributions of the antagonists in
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