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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
158 Postharvest Diseases of Fruits and Vegetables
such as benomyl or iprodione, which are active against Monilinia (Eckert
and Ogawa, 1988).
Sulfur dioxide (SO2) is appHed as a postharvest fumigation to grapes
in order to eradicate spores of Botrytis cinerea, to inhibit very superficial
infections on the fruit and, above all, to prevent the contact spread or
'nesting' of the fungus on grapes during storage. The tolerance of grapes
to SO2 is higher than that of all other fruits and vegetables; however,
even for grapes an effective combination of concentration and time has to
be carefully chosen in order to compromise between effective decay
control and minimum fruit injury as exhibited by bleaching and stem
drying (Eckert and Ogawa, 1988). In a recent study Coertze and Holz
(1999) found that exposure of grapes to SO2, similarly to prolonged cold
storage, reduced the resistance of the berry to infection by individual
conidia of B. cinerea, and could result in an increased rate of lesions.
Individual conidia did not induce disease on the fresh, resistant berries.
A common fumigation procedure consists of an initial application of
0.5% SO2 (v/v) for 20 min, immediately after harvest, followed by
low-concentration (0.1-0.2%) fumigation for 30-60 min every 7-10 days
during the storage period. Another procedure involves applications of
reduced levels of sulfur dioxide (0.2% SO2) three times weekly, which
results in less residual bisulfite in the grapes, with less bleaching than
the traditional high dosage treatment (Marois et al., 1986). In California,
Australia, South Africa, Chile and Israel, the exposure of grapes to SO2
during export shipments is carried out by adding a bisulfite or
metabisulfite salt to the packaging material (Nelson, 1985; Guelfat-Reich
and Safran, 1973). The SO2 is released into the atmosphere around the
grapes and prevents infection with S. cinerea when in contact with
infected berries. Liquid or solid SO2 formulations which have been
developed (Combrink and Truter, 1979; Guelfat-Reich et al., 1975;
Kokkalos, 1986), release the SO2 after the package has been closed, and
maintain efficient concentrations (5-10 ppm) of SO2 in the atmosphere,
which prevent contact-infection during prolonged storage. Studies of the
efficacy of a range of S02-generating pads in stored grapes showed that
some properly regulated pads were capable of controlling Botrytis rot in
table grapes even when moderate levels of initial inoculum were present
(Mustonen, 1992).
SO2 fumigation at 1600 ppm for 20-30 min or 3200 ppm for 5 min gave
almost complete control of Botrytis storage rot of kiwifruit in New
Zealand (Cheah et al., 1993). Absorption of SO2 by the fruit gradually
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