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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
314 Postharvest Diseases of Fruits and Vegetables
the senescent calyx. Infection of the fruit by Mucor frequently occurs
following contamination by soil splash after heavy rain (Dennis, 1983a).
Infection by Alternaria (and sometimes also by Stemphylium) via the
calyx end similarly occurs in the field prior to harvest, and may result in
premature fall of infected berries from the bushes. The fungus initially
colonizes the seeds. However, when the fruits are stored at ambient
temperatures, the fungus can progress and begin to infect the pericarp.
Control Measures
Chemical control of postharvest diseases of soft fruits has mainly
focused on the suppression of B. cinerea, the most important pathogen of
these fruits. Since infection originates in the field, fungicidal sprays
during the flowering period are the first step in controlling the disease.
Preharvest fungicidal application of benzimidazole successfully
controlled decay in the early 1970s (Jordan, 1973). Following the
emergence of 5. cinerea strains resistant to these chemicals, they have
been replaced by fungicides of the dicarboximide group, and preharvest
spraying of strawberries with iprodione during the flowering period
provided good control of the gray mold disease during storage (Aharoni
and Barkai-Golan, 1987). However, these fungicides, similarly to the
benzimidazoles, are not effective against Phycomycetes fungi, such as
Rhizopus spp. and Mucor spp. (Eckert and Ogawa, 1988), and B, cinerea
strains resistant to the dicarboximides have also developed (Hunter et
al., 1987). Postharvest fungicidal applications are not practical for ripe
berries because of their sensitivity to wetting.
A rapid reduction of the temperature from the field level to below 5°C
is important for retarding decay development in strawberries during
shipment (Harris and Harvey, 1973). This is currently achieved by
forced-air cooling, although hydrocooling, which removes field heat from
the berries more rapidly than air cooling, cleans them and does not cause
moisture loss. The latter has not been recommended because wetting
may lead to excessive decay (Mitchell, 1992). In a recent study of the
decay hazards associated with hydrocooling, Ferreira et al. (1996)
concluded that hydrocooling, with the addition of proper chlorination, has
promise as a method for rapid cooling and cleaning of strawberries as
well as for reducing the level of S. cinerea inoculum on the fruit surface.
These investigators considered that if cooled, good-quality berries were
subsequently stored at the low temperatures recommended (0 to 1°C),
the risk associated with hydrocooling would be minimal.
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