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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Physical Means 199
(46-49°C) for 4 min arrests development of Phytophthora citrophthora,
the causal agent of brown rot, only if the fungus has not yet penetrated
the outer layer of the rind. Furthermore, factors affecting the rate of
fungal development and its progress in the fruits, prior to harvesting,
such as the temperature prevailing in citrus groves during the rainy
season, may also determine the efficacy of heat treatment in arresting
decay (Schiffmann-Nadel and Cohen, 1966).
The increased water loss that often follows hot water treatment can be
reduced by applying wax, with or without fungicides (Wells, 1972), or by
wrapping the produce in plastic film before or after heat treatment
(Anthony et al., 1989; Teitel et al., 1989). Such a wrapping may protect
the fruit, not only from water loss but also from recontamination and
discoloration (Barkai-Golan and Phillips, 1991). The fruit may also be
protected from heat injury by preconditioning. Lemons that were slightly
wilted or had been kept for 2-8 days at 15.5°C prior to heating, were more
tolerant to heat than those exposed to the high temperature immediately
after picking (Houck, 1967). On the other hand, the benefits of heat
treatment may be augmented by enhanced pathogen sensitivity to high
temperatures. Alternaria rot was controlled more effectively in tomatoes
heat-treated 8 h after inoculation than in those treated immediately after
inoculation (Barkai-Golan, 1973); the spores that had germinated during
that period, as well as the germ-tubes or the young hyphae, were more
sensitive to heat than non-germinated spores.
The efficacy of postharvest hot water dipping in decay suppression has
been reported for many host-pathogen combinations. Among these are:
P. citrophthora and Penicillium digitatum in citrus fruits; Colletotrichum
gloeosporioides in mangoes; various fungi in papayas and melons;
Monilinia fructicola in plums; M fructicola and Rhizopus stolonifer in
peaches and nectarines; and Gloeosporium spp. and Penicillium
expansum in apples. The efficacy of moist hot air treatment (43°C, 30
min) in decay control was reported for species of Botrytis, Rhizopus,
Alternaria and Cladosporium in strawberries (Barkai-Golan and Phillips,
1991). Although hot water treatment of strawberries has generally
resulted in fruit injury, a recent study with strawberries of cv. Tudela
showed that dipping the fruit at 44 or 46°C for 15 min delayed B, cinerea
development, with good retention of firmness and no development of
off-color or off-flavor (Garcia et al., 1996). Of all the effective heat
treatments, the one most commonly used commercially is that applied on
mangoes. In this treatment, the fruits are immersed for 15 min in hot
water (50-55°C) prior to storage, to prevent anthracnose development
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