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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Chemical Control 155
In some instances, however, several hours delay between the picking
and the chemical treatment will not reduce the effectiveness of the
treatment, and may even increase it. The increased efficiency of the
delayed treatment may be related to the fact that germinating spores are
more sensitive to the treatment than dormant spores (Eckert, 1978).
Since, in practice, a few hours will generally elapse between harvest and
treatment, application of the chemical should take place as soon as
possible after harvest in order to avoid further development of the
germinating spores in the host tissue. In the case of quiescent infections,
such as anthracnose (Colletotrichum gloeosporioides) in tropical and
sub-tropical fruits, and lenticel rotting (Gloeosporium spp.) in apples, in
which the pathogen remains confined to the tissue beneath the peel,
because of host resistance, it is permissible to delay the systemic
fungicide application until several weeks after inoculation (Eckert, 1978).
During the last 50 years, more than 30 organic compounds have been
introduced for controlling decay by postharvest application. The selection
of the appropriate compound depends on: (a) the sensitivity of the
pathogen to the chemical substance; (b) the ability of the substance to
penetrate through surface barriers into the infection site; and (c) the
tolerance of the host, as expressed both by injury and other phytotoxic
effects, and by any adverse effect upon the quality of the product (Eckert
and Ogawa, 1985). The 'first generation' of postharvest fungicides
includes diphenyl, sodium orit/io-phenylphenate, dicloran and
sec-butylamine. These compounds are effective in preventing decay
caused by wound pathogens, such as species of Penicillium and Rhizopus,
but they have little effect on quiescent infections, or other infections
situated within the host tissue (Eckert, 1977).
Biphenyl (diphenyl) is a fungistat that has been used extensively by
citrus exporters for more than five decades. It played a most important
role in the development of distant markets for citrus fruits and of the
world trade in these fruits. The fungistat may be impregnated into paper
wraps on each individual fruit, or into paper sheets placed beneath and
above the fruits within the container. It sublimes slowly into the
atmosphere and protects the fruits during the entire period of shipping to
distant markets. The main function of biphenyl is the inhibition of
sporulation of Penicillium spp. (P. digitatum and P. italicum) on
decaying fruits. Because of this action, biphenyl prevents contact
infection of adjacent sound fruits by fungal spores which normally cover
the surface of decayed fruit. However, this compound is only weakly
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