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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
36 Postharvest Diseases of Fruits and Vegetables
development is related to both the pathogen spore load on the fruit or
vegetable surface and the availability of wounds for penetration. In fact,
the control of postharvest infections initiated by *wound pathogens' is
based primarily on the reduction of the inoculum level that may reach
the host, along with continuing efforts to reduce pre- and postharvest
injury. Regular sanitation in the field, in the packinghouse and in the
storerooms, will all contribute to the reduction of the spore load on the
harvested produce, while careful handling and prevention of mechanical
damage will help to reduce the number of entry points for the pathogen.
Discussing postharvest diseases of pome and stone fruits, Edney
(1983) states that the incidence of rotting is influenced by the number of
viable spores at potential infection sites when the fruit is at the stage of
ripening suitable for infection to develop. However, the amount of
inoculum present is closely related to weather conditions during the
growing season, particularly when the spores are dispersed by rain as in
the cases of Gloeosporium and Phytophthora species.
An interaction between wounding and inoculum level has been
described for the brown rot fungus, Monilinia fructicola on stone fruits
(Hong et al., 1998). In the presence of a high level of fungal inoculum on
the fruit surface, penetration of the unwounded fruit can take place
through the stomata or directly through the peel. However, as the spore
load on the fruit decreases below a certain level (5 or 50 spores per mm^
for nectarines or peaches, respectively) the significance of wounds as
entry points increases. With plums, on the other hand, brown rot can
develop only on wounded fruit, even at an inoculum level of 10^
spores/ml.
Studying surface colonization and lesion formation by various
inoculum densities of single conidia of Botrytis cinerea on grapes, Coertze
and Holz (1999) found that individual conidia readily infected cold-stored
berries, which are highly susceptible to infection, and that the number of
lesions tended to increase at high inoculum concentrations. However,
these conidia did not induce disease symptoms on fresh, resistant berries,
irrespective of the inoculum density. These results suggested that
infection was not always governed by conidial density on berry surfaces,
but rather by the level of host resistance.
The inoculum level of the pathogen may determine the success of
biological control of postharvest diseases with antagonistic
microorganisms (see the chapter on Biological Control). For various
host-pathogen interactions, the efficacy of the antagonistic
microorganism in reducing decay has frequently been affected by the
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