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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Biological Control 243
time and space, and of their nutritional *niche' differentiation. The
microorganisms in these mixtures, which were isolated from exposed
apple tissue before harvest, comprised mainly yeast populations.
Following screening for their ability to control P. expansum on apple
fruits, they were grouped into various nutritional clusters. Preference
was given to antagonists colonizing the same fruits, followed by those
colonizing different fruits but isolated at the same time. Nutritional
differences between two antagonists in a mixture allowed populations of
both antagonists to flourish in the same wound. The results indicated
that combinations of antagonists that occupy different nutritional niches
and coexist in the infection area are more effective in biological control
treatments than the individual antagonists.
The advantage of antagonistic pairs over a single antagonist was
described by Schisler et al. (1997) in the control of Fusarium dry rot
(Gibberella pulicaris, anamorph Fusarium sambucinum) in stored potato
tubers. The search for biological means to control this disease was
stimulated by the development, over the years, of resistance to
thiabendazole, the conventional chemical treatment. When the pathogen
was challenged with pairs of antagonistic bacterial strains, it was found
that successful pairs reduced Fusarium dry rot by an average of 70%
versus controls, a level of control comparable with that obtained with 100
times the inoculum dose of a single antagonist strain. The successful
coexistence of these pairs was partly attributed to the fact that
compatible strains possessed differing carbon substrate utilization
profiles. Similarly to the demonstration by Janisiewicz (1996) that
combining antagonists on the basis of *niche' differentiation enhanced the
possibility of improved control of P. expansum on apples, diverse niches
are also likely to be found in potato wounds. These could result in the
exposure of G. pulicaris to higher total bacterial populations and wider
ranges of nutrient competition when challenged by co-existing mixtures
of microbial strains than when challenged by a single antagonist
(Schisler et al., 1997). It does seem that determination of the substrate
utilization profiles of strains of antagonist pairs, as well as evaluation of
the colonization characteristics of successful and unsuccessful pairs of
potato dry rot antagonists, would provide further clues as to the nature
of the disease control success of some antagonistic pairs. However, the
success of antagonistic pairs also may be attributable to the individual
strains of the pair possessing complementary modes of action (Schisler et
al., 1997).
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