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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Biological Control 247
Compatibility between a microbial antagonist and a synthetic
fungicide offers the option of using the antagonist in combination with
reduced levels of the fungicide. Applying the yeast antagonist, Pichia
guilliermondii to citrus fruit in combination with substantially reduced
concentrations of thiabendazole (TBZ) reduced Penicillium digitatum
decay to a level similar to that achieved by the currently recommended
concentration of TBZ applied alone (Droby et al., 1993b). Thus, by
adapting an integrated pest management system, we may expect not
only to gain effective pest control but we can also maintain very low
levels of chemical residues (Hofstein et al., 1994). The biological agent
must, however, have low sensitivity to any of the supplemented chemical
fungicides.
The intensive studies on biocontrol of postharvest diseases have led to
the registration of two biological products for commercial postharvest
applications to citrus fruits: Aspire, which is Candida oleophila, and
BioSave'^ 1000, which is Pseudomonas syringae (Brown, G.E. and
Chambers, 1996; Brown, G.E. et al., 2000). In evaluating the efficacy of
biological products for the control of citrus fruit pathogens. Brown and
Chambers (1996) found that significant control of P. digitatum was
obtained by each of the biological products but that the level of control, as
well as consistency, were usually less pronounced than those obtained
with standard rates of the fungicides, thiabendazole or imazalil. More
recently Brown, G.E. et al. (2000) found that the major factor affecting
the efficacy of the biological control is how quickly and how well the yeast
colonizes injuries to the citrus fruit surface, including minor injuries
involving only oil vesicles. This indication followed the finding that the
peel oil was toxic to the Candida cells but not to spores of P. digitatum.
However, combining Aspire with each of the chemicals used improved the
results; sometimes combinations with a low rate of fungicide were
sufficient to achieve effects similar to those obtained by the chemicals at
standard rates.
GRAS (generally recognized as safe) compounds or natural products of
plant origin, which have been suggested as alternatives to synthetic and
conventional fungicides (see the Chapter on Chemical Control - Generally
Recognized as Safe Compounds and Natural Chemical Compounds),
could also be used in combination with biocontrol agents, complementing
their activity. Pathogens treated with such antifungal substances might
be weakened and become more vulnerable to the antagonist activity
(Pusey, 1994).
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