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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
200 Postharvest Diseases of Fruits and Vegetables
(Spalding and Reeder, 1986b). The traditional hot water treatment (48°C,
20 min) has been used successfully in Hawaii to control C. gloeosporioides,
stem-end rots and incipient Phytophthora infection in papaya (Aragaki et
al., 1981). However, several problems, such as delayed color development
and increase in Stemphylium rot, arose from the hot water application
(Glazener and Couey, 1984).
Following the withdrawal of ethylene dibromide as a pesticide against
fruit flies on papaya in 1984, the double hot water dip (42°C for 30 min
followed by 49°C for 20 min) has been adopted for fruit disinfestation in
papaya shipments to fruit fly-free zones. The double-dip procedure also
provides postharvest disease control when coupled with field fungicide
sprays (Alvarez and Nishijima, 1987). However, various papaya cultivars
are sensitive to heat, and the fruit becomes increasingly susceptible to
heat injury as it ripens. A single hot water dip at 49°C for 15 min was
reported by Nishijima (1995) to be the optimum treatment for disease
control with minimum detrimental impact on fruit quality.
The basic problem in short-term treatments is the high temperature
needed for decay suppression. Such a temperature is often near the level
injurious to the commodity and it must, therefore, be carefully measured
and controlled. Furthermore, temperatures too high for a given host may
increase the host susceptibility to pathogens, even when no visible
damage develops (Phillips and Harris, 1979).
Combined Applications
Over the years, combined heat-plus-chemical treatments have been
developed in order to achieve decay control by using lower temperatures
and shortened exposure time on the one hand, and reduced fungicide
concentration, on the other. The improvement may be due to the more
effective infiltration of the fungicides into the wound sites on the fruit,
that are exploited by the fungus (Brown, G.E., 1984).
Hot water containing fungicides has been found more effective than
either of the separate treatments alone in controlling Rhizopus stolonifer
infection in peaches, plums and nectarines (Wells and Harvey, 1970). The
addition of thiabendazole, benomyl, captan or botran (dicloran) to water
heated to 52°C enabled the immersion time to be reduced from 15 to 0.5
min, without affecting decay control. Hot suspensions of benomyl or
botran were similarly more effective than unheated suspensions, in
controlling brown rot (Monilinia fructicola) in peaches (Smith, W.L.,
1971). Combinations of fungicides at a quarter of the recommended rates
with 1.5-2-min dips in hot water at 51.5 and 54.5°C were equally or more
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