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

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Chemical Control 173
carbonate, potassium carbonate, sodium bicarbonate, ammonium
bicarbonate and potassium bicarbonate were 5.0, 6.2, 14.1, 16.4 and
33.4 mM, respectively. All these compounds were fungistatic: spores
removed from the solutions resumed germination when incubated in
potato dextrose broth. In spite of the differences between the effects of
sodium bicarbonate and sodium carbonate on spore germination, the two
solutions were similarly effective in controlling the green mold in lemon
and orange fruits inoculated 24 h before treatment. Therefore, the in
vitro toxicity of the solutions does not indicate their efficacy in controlling
decay. Since bicarbonate anion concentration is related to pH, this
parameter was examined in combination with several salts to separate
pH effects from the bicarbonate effects on B. cinerea growth (Palmer et
al., 1997). It was found that as the pH increased from 7.0 to 8.5, colony
growth on media supplemented with bicarbonates and phosphates
decreased more than could be accounted for from pH alone.
Potassium bicarbonate was found to inhibit spore germination,
germ-tube elongation and mycelial growth of B, cinerea and A, alternata,
the main postharvest pathogens of bell pepper fruits. Its action was
fungistatic rather than fungicidic: mycelial plugs of both fungi, when
transferred from potassium bicarbonate-amended PDA to unamended
medium, grew similarly to unamended controls (Fallik et al., 1997). At
concentrations greater than 1% for Botrytis or 2% for Alternaria, mycelial
mats remained white because of the inability of the fungi to sporulate.
Scanning electron microscopy analysis revealed that the fungistat caused
shrinkage and collapse of hyphae and spores, resulting in the prevention
of normal sporulation. A 2-min pre-storage dip of red sweet peppers in 1
or 2% potassium bicarbonate reduced decay incidence to a commercially
acceptable level during a storage and marketing simulation. However, a
longer dipping time, especially at higher salt concentrations (3%),
reduced fruit quality, as indicated by decreased firmness and further
decay development (Fallik et al., 1997). Collapse of hyphal walls and
shrinkage of B, cinerea conidia were suggested to be partly due to the
reduction in fungal cell turgor pressure or the increase of the
permeability of the fungal cell membrane, caused by the bicarbonate ion
(Palmer et al., 1997; Fallik et al., 1997).
A direct inhibitory effect of sodium bicarbonate on in vitro mycelium
growth was similarly recorded for K stolonifer, A. alternata and
Fusarium spp., the major pathogens of stored melons (Aharoni et al.,
1997). Coating harvested melons with wax containing 2% sodium
bicarbonate resulted in a marked reduction in decay incidence after
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