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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Chemical Control 175
with calcium hypochlorite or sodium hypochlorite, is a standard
procedure to disinfect various fruits and vegetables in the packinghouse.
Its main effect in reducing decay development is via reduction of the level
of inoculum in the treated water (see the chapter on Chemical Control -
Sanitation). Chlorine acts on fungal propagules by direct contact and can
inactivate spores which are suspended in water or located on the surface
of fruits or vegetables. It does not act on pathogens under the fruit skin
or after infection has occurred. Because of the rapid drop in the biocidic
activity of chlorine in the presence of organic substances (that modify the
pH of the solution), it has frequently been replaced by chlorine dioxide
(CIO2), which is more stable than chlorine and is effective over a wide pH
range (Bartz and Eckert, 1987). In addition, CIO2 is not corrosive to the
packinghouse equipment.
In a recent study, CIO2 has been evaluated for its effectiveness in
controlling the brown rot caused by M laxa in stone fruits (Mari et al.,
1999). CIO2 was found to affect M laxa conidia directly, and at 100 |ig/ml for
20 s or 50 |Lig/ml for 1 min, totally inhibited their germination. The direct
effect of the chemical on fungal spores has also been exhibited in vivo, when
decay development in nectarines and plums, wounded and inoculated with
C102-treated conidia, was markedly suppressed. Under these conditions,
however, the effects varied with the CIO2 concentration, the time of
exposure of the conidia, and the species of fruit tested (Mari et al., 1999).
For table grapes, that cannot be subjected to water immersion
treatments without altering their quality, a modified chlorine
atmosphere with a relatively long residual effect has been developed
(Zoffoli et al., 1999). Chlorine gas (CI2) produced by a salt mixture of
calcium hypochloride [Ca(0Cl)]2, sodium chloride (NaCl) and calcium
chloride (CaCb) with citric acid, combined with cold storage (25 days at
0°) significantly reduce Botrytis rot in both inoculated and field-infected
grape cultivars. Infections by conidia or mycelium of J3. cinerea were
suppressed for up to 45 days in cool storage and no deleterious effect of
chlorine gas generation was detected. This procedure was suggested to be
an alternative to SO2 treatment for controlling decay in table grapes,
since the latter frequently leaves residues exceeding the tolerance limits
registered in the US (Zoffoh et al., 1999).
Sugar analogs have long been known to affect metabolic processes of
fungi and plant cells (Moore, 1981). The compounds 2-deoxy-D-glucose
and L-sorbose were found to interfere with the growth of several
filamentous fungi and yeasts when used as a sole carbon source (Biely
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