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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
254 Postharvest Diseases of Fruits and Vegetables
in the fruit peel during ripening (Prusky et al., 1985b). Thus, by
producing a high-C02 atmosphere, the increased concentrations of
epicatechin during ripening may lead to increased antifungal activity in
the host and, therefore, to maintaining the quiescent state of the fungus
and reducing decay development.
A high-C02 atmosphere may also induce higher levels of resorcinols in
mango fruits, resulting in the retardation of Alternaria alternata
infection (Prusky and Keen, 1995). Similarly, application of
subatmospheric pressure to mango fruits retards ripening and, in
parallel, retards the decrease in the level of the preformed antifungal
resorcinol compounds in the peel. This decrease occurs naturally
during ripening. Under these conditions the renewed development of
A. alternata, which is found in a quiescent state in the fruit, is delayed
(Droby et al., 1986).
Heat Treatments
Heat treatment can affect many physiological processes of the
harvested fruit and vegetable. Depending on fruit species, cultivar, and
physiological age, on the one hand, and on the temperature and length of
exposure to heating, on the other hand, this treatment may lead to
retardation of the ripening process. In many cases, along with the
retardation of fruit ripening and the maintenance of firmness during
storage, heating may also induce enhanced resistance of the host to
pathogens.
Various mechanisms by which heat treatment may induce host
resistance have been suggested. Heat may function as a stress factor,
inciting the accumulation of phytoalexins in the host tissue. A range of
coumarin-derived antifungal compounds was detected in the peels of
citrus fruits, following heat treatment (Ben Yehoshua et al., 1992; Kim et
al., 1991). Kim et al. (1991) reported on the enhanced accumulation of
the antifungal coumarin scoparone in heat-treated Penicilliuminoculated
lemon fruits, and a correlation was drawn between the level of
the antifungal activity in the host tissues and the development of disease
resistance. Heat treatments may also result in the inducement of specific
proteins of various molecular weights, known as 'heat shock proteins', in
the plant tissue (Freeman et al., 1989; Vierling, 1991). A correlation was
drawn between the accumulation of *heat shock proteins' and the
enhancement of thermotolerance of the fruit following heat treatments.
The inducement of such proteins in fruits and their consequent enhanced
thermotolerance may improve the efficacy of heat treatments in reducing
http://arab2000.forumpro.fr