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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Factors Affecting disease Development 51
Relatively high levels of ethylene, that were found to accumulate in
strawberry punnets overwrapped with polyethylene during marketing,
were suggested to be the contributing cause to enhanced postharvest
loss. The addition of an absorbent containing potassium permanganate
was found to be an effective means of reducing ethylene in strawberry
punnets during marketing, at ambient or reduced temperatures, with a
corresponding increase in storage life. The potassium permanganatetreated
fruit was less susceptible to B. cinerea, which is the main cause
for deterioration at 20°C (Wills and Kim, 1995). With regard to the effect
of ethylene on Botrytis in tomatoes, this gas was found directly to
stimulate germ-tube elongation of fungal spores when introduced into
tomato fruit tissue; but when the fruit is exposed to ethylene prior to its
inoculation by the fungus, the gas may stimulate the pathogen
development indirectly because of the stimulation of fruit ripening
(Barkai-Golan et al., 1989a). Indirect stimulation of fungal growth occurs
in normal tomato fruits at the mature-green stage, on which exogenous
ethylene can normally act, but will not occur in non-ripening tomato
mutants (nor) in which ripening cannot be induced by ethylene
application (Barkai-Golan et al., 1989b). Exposure to ethylene also
resulted in the stimulation of ripening in young mango fruits. Along with
fruit ripening, the concentration of the antifungal resorcinol compounds
was decreased and the sensitivity of the fruit to A. alternata was
enhanced (Droby et al., 1986).
In contrast to cases in which exposure to ethylene stimulates disease
development, in other cases it does not affect disease development, and
may even enhance host resistance to pathogen attack. Induction of
resistance to decay by ethylene was reported for sweet potatoes infected
by Ceratocystis fimbriata (Stahmann et al., 1966), and tangerines
exposed to ethylene for 3 days prior to their inoculation with C.
gloeosporioides (Brown, G.E. and Barmore, 1977).
E. HOST-PATHOGEN INTERACTIONS
A pathogen that has reached a suitable host and also finds conditions
suitable for germination, for penetration into the host, and for
establishment within its tissues, will develop and cause a disease only if
it succeeds in withstanding the protective means of the host. In other
words: the struggle between the pathogen attack capability and the
http://arab2000.forumpro.fr