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

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Factors Affecting disease Development 49
Similarly, the addition of cycloheximide, which is a protein-synthesis
inhibitor (Riov, 1974), to the abscission zone of debuttoned fruits during
early stages of degreening with high ethylene concentrations, also
suppressed disease development. In other words, the inhibition of the
enzymatic activity led to reduced fruit susceptibility to stem-end rot
development.
The correlation between ethylene application to citrus fruit and the
enhancement of fruit susceptibility to the green mold rot (Penicillium
digitatum) has been attributed to the reduction in the antifungal activity
of the peel: ethylene treatment stimulates the natural reduction in the
amount of the antifungal citral and thus stimulates decay development
(Ben-Yehoshua et al., 1995). Brown, G.E. and Barmore (1977) showed
that anthracnose development in tangerines infected with Colletotrichum
gloeosporioides occurred only when the fruits had been exposed to
ethylene immediately after inoculation. In this case, disease induction by
ethylene probably resulted from the stimulation of the infection hyphae
production by the appressoria found on the fruit exposed to ethylene, and
their penetration into the epidermis cells.
Flaishman and Kolattukudy (1994) reported that ethylene treatment
at concentrations much lower than those produced during ripening of
climacteric fruits, was capable of inducing both conidia germination and
appressoria formation in Colletotrichum musae and C. gloeosporioides,
and that endogenic ethylene, produced in climacteric fruits during
ripening, can serve as a signal for the termination of the appressoria
latency on the fruit. The induction of appressoria formation does not take
place in Colletotrichum species attacking non-climacteric fruits, such as
citrus fruits. When spores of this fungus come into contact with citrus
fruits, which normally do not produce a considerable amount of ethylene
after harvest, appressoria will not be produced in large quantities, and
the fungus will not cause a serious decay. However, when such a fruit is
exposed to ethylene during degreening, an abundance of spores is
produced and a massive infection of the fruit takes place, as was
previously reported for ethylene-treated citrus fruits (Brown, G.E., 1975).
In a later study, however, Prusky et al. (1996) differentiated between
the effect of ethylene on the climacteric process and ripening of avocado
fruits, on the one hand, and, on the other hand, the process of initiation of
lesion growth from quiescent appressoria of C. gloeosporioides. They found
that ethylene treatment at 45 |il l-i, applied to immature avocado fruits.
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