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

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Postharvest Disease Summary 277
Recently, two biological products have been registered for commercial
postharvest applications to citrus fruits - Aspire, which is Candida
oleophila, and BioSave"^^ 1000, which is P. syringae (Brown, G.E. and
Chambers, 1996). Evaluating the efficacy of these biological products
against citrus fruit pathogens, G.E. Brown and Chambers (1996) found
that although significant control of P. digitatum was obtained with each,
the level of control and its consistency were usually less pronounced than
those obtained with standard rates of the usual chemicals (thiabendazole
or imazalil). Combining each of these chemicals with Aspire improved the
results and sometimes combinations of Aspire, with a low rate of
fungicide, were sufficient to achieve effects similar to those obtained by
the chemicals at standard rates. The biological products were not
effective against stem-end rots caused by Diplodia natalensis or
Phomopsis citri (Brown, G.E. and Chambers, 1996).
Several approaches have been used to control stem-end rots of citrus
fruits arising from latent infections. Since infections at the stem end are
related to the ability of the pathogens to invade the fruit through the
senescent button tissues, these fruits have been controlled for over four
decades with 2,4-D in order to retard senescence of the button, which
usually harbors a quiescent infection of one of the stem-end pathogens.
Maintaining the button green and young delays fungal penetration into
the fruit (Eckert and Eaks, 1989).
Debuttoning of fruit at harvest was found to remove the source that is
responsible for initial infection. Similarly, pruning out dead limbs and
twigs to reduce the level of inoculum has also been found effective, but it
is not economically practical (Smoot et al., 1983). The control of stem-end
rots of citrus fruits was made possible by the introduction of the systemic
fungicides (thiabendazole, benomyl, imazalil and prochloraz). Apparently,
these systemic compounds penetrate the tissues and provide action
against the pathogen at sites not accessible to the traditional
water-soluble fungicides (Brown, G.E., 1981; Eckert, 1990).
Since brown rot is initiated in the grove, its control should start with
preharvest disease control. Fungicidal sprays of fixed copper compounds
applied to the lower fruits of the tree before the onset of the rainy season
were found beneficial in suppressing disease development (Timmer and
Fucik, 1975). Spraying the ground beneath the trees was found effective
in inhibiting spore formation on the soil surface (Solel, 1983). Preventive
measures also include the removal of fallen fruit from the grove, routine
disinfection of the picking boxes and ensuring that they are not left on
the soil during rainy or foggy periods (Smoot et al., 1983).
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