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

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Physical Means 209
phytoalexins, rishitin and lubimin formed in potato tubers and rishitin
formed in tomato fruits, in response to infection, were reduced after
gamma irradiation at doses required for potato tuber sprout inhibition
(100 Gy) and for tomato fruit shelf-life extension (3 kGy).
The formation of antifungal compounds in the host in response to
radiation may be one factor in the complex of radiation effects on the
pathogen, although its importance in disease suppression has not yet
been evaluated.
Radiation Effects on the Disease
An important advantage of gamma radiation over most chemical
treatments, which derives from its short wavelength, is its ability to
penetrate into the tissues. This enables irradiation to reach not only
microorganisms in wounds, but also those located within the host, as
quiescent or active infections. Thus, we may also refer to irradiation as a
therapeutic means, effective after infection has already started. However,
the use of irradiation for decay suppression is basically determined by
the tolerance of the host to radiation, rather than the fungicidal dose
required for pathogen suppression; different host species, and even
different cultivars of a given species, may differ in their tolerance to
radiation. Furthermore, dose tolerance may be influenced by the state of
fruit ripeness at the time of treatment and by the subsequent storage
conditions (Maxie and Abdel-Kader, 1966).
Early studies in the 1950s and 1960s had already established that
fruits and vegetables are usually susceptible to radiation doses that are
lethal to the common postharvest pathogens. However, the same studies
also indicated that extension of the postharvest life of several
commodities could be achieved by using sublethal doses, which could
temporarily inhibit fungal growth and, therefore, prolong the incubation
period of the disease. Such a prolongation could be sufficient to control
decay in fruits with a short postharvest life, for which even a few
additional lesion-free days are valuable.
The best example of such a fruit is the strawberry, for which a dose of 2
kGy may be sufficient to prevent decay for several days, without causing
fruit injury or changes in the ascorbic acid content (Maxie et al., 1964;
Barkai-Golan et al., 1971). However, one has to keep in mind that different
cultivars of strawberries may respond differently to irradiation. Irradiating
naturally infected strawberries of cv. Lassen with a 2-kGy dose,
Barkai-Golan et al. (1971) found that the incubation period of gray mold at
15°C was extended from 3 days to 10 days, and that the subsequent
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