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

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Biological Control 245
and P. expansum, or to lemon and orange wounds prior to inoculation with
P. digitatum, significantly enhanced the biocontrol activity of C. saitoana
against decay. The same combination was also effective against
established infections when applied within 24 h after inoculation. In other
words, the combination of the antagonistic yeast with the sugar analog
had both protective and curative effects against the postharvest
pathogens. Furthermore, its effectiveness on citrus fruits was found to be
similar to that of the common fungicide, imazalil. It was also emphasized
that the curative activity gained by the combined treatment represented
an improvement over the currently available microbial biocontrol products
that confer only a protective effect (El Ghaouth et al., 2000b).
Another combination aimed at improving the biocontrol of fruit decay
by C. saitoana is that of the antagonistic yeast with glycolchitosan, a
combination known as "a bioactive coating" (El Ghaouth et al., 2000a).
The use of a bioactive coating became possible because the presence of
glycolchitosan in apple wounds and on the fruit surface does not affect
the natural increase of the yeast population. The combination of the
antagonistic yeast with 0.2% glycolchitosan was more effective in
controlling the natural infection caused by B. cinerea and P. expansum in
various apple cultivars than either the yeast or the glycolchitosan alone.
The bioactive coating was either similar or superior to thiabendazole in
suppressing decay; it was also more effective than the antagonistic yeast
alone in controlling natural infection of oranges and lemons (mainly by
P. digitatum) and the control level was equivalent to that achieved with
2000 g ml-i imazalil (Fig. 41).
Genetic manipulation of biocontrol fungi is another approach to
improving the antagonist ability to control disease. To enhance their
antagonistic potential against pathogenic fungi, Lalithakumari et al.
(1996) selected two parent isolates of Trichoderma species for genetic
manipulation: Trichoderma harzianum, which is an efficient biocontrol
agent against plant pathogens, and Trichoderma longibrachiatum, which
is tolerant to copper sulfate and carbendazim. The second isolate was
selected as a co-parent because development of fungicide tolerance
potential in a biocontrol agent is believed to be of great importance for
integrated disease management. It was found that protoplast fusion of the
two isolates, taken from young mycelia following cell-wall digestion,
resulted in fusants that exhibited an enhanced antagonistic effect against
several pathogens, along with tolerance to copper and carbendazim.
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