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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Biological Control 235
visible injury and prevented green mold development when it was applied
within 12 h of inoculation. Laboratory tests confirmed that fimgal inhibition
in vitro was caused by the presence of psrrrolnitrin in the culture medium.
However, experiments also showed that when the fruit was inoculated
with pyrrolnitrin-resistant P. digitatum mutants, inhibition of decay
development was still recorded, even though the spores of the resistant
isolate were capable of germination in the presence of the antibiotic
substance. This result suggests that the antibiotic substances produced by
the Pseudomonas are not the only means by which the bacterium
functions, and that the presence of Pseudomonas cells in the wound also
involved a similar antifungal effect. Furthermore, another species of
Pseudomonas - P. fluorescence - which had no inhibiting effect on the
Penicillium growth in culture, was capable of significantly reducing the
growth rate of the green mold in the harvested fruit.
Various antibiotic compounds which control human diseases have
been tested against plant diseases: chlortetracycline, cycloheximide,
fungicidin, griseofulvin, mycostatin and streptomycin, were found to be
effective in controlling serious postharvest diseases. These include
bacterial soft rot caused by Erwinia carotovora, gray rot caused by
B, cinerea and brown rot caused by M fructicola (Goodman, 1959).
However, none of these compounds is used commercially to control
postharvest diseases since, in addition to their high cost, their
application to fresh fruits and vegetables would endanger their medicinal
effectiveness when needed by humans (Pusey, 1991). The possibility of
rapid development of pathogen resistance towards antibiotic substances
may be another obstacle in the practical use of antibiotic-producing
microorganisms for decay control.
As the list of microorganisms effective in suppressing pathogen
development without being capable of producing antibiotic compounds
grows, much research has been focused on understanding and defining
their mode of action in the fruit.
(b) Competition for nutrients between the antagonist and the
pathogen. A fresh wound is a good source of nutrients for invading
microorganisms. A delicate balance apparently exists at the wound site
between the propagules of the antagonist and the pathogen, which affects
the interaction between them and will determine whether or not the
wound becomes the site of infection. As was previously mentioned, to
compete successfully with the pathogen at the wound site, the antagonist
should be better adapted than the pathogen to various environmental and
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