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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Chemical Control 167
Studies carried out 10 years later (Ferrin and Kabashinna, 1991),
described the development of metalaxyl-resistant isolates of
Phytophthora parasitica, with EC50 values for inhibition of linear
mycelial growth exceeding 700 \xg ml-i, as compared with values of
0.25-3.08 |Lig ml-i for the sensitive isolates. However, the resistances to
the mycelium growth may differ from that for the formation of sporangia
or chlamidospores.
Metalaxyl-resistant genotypes emerged rapidly worldwide and are
responsible for a lack of Phytophthora infestans control in potatoes and
tomatoes. A cross-resistance was reported for this class of fungicides, and
the metalaxyl-resistant isolates were also resistant to oxadixyl, while
the metalaxyl-sensitive isolates were also sensitive to oxadixyl; both of
these are systemic fungicides (Sedegui et al., 1999). Resistance to
metalaxyl, which is mediated by a single gene (Cooke, 1991), has evolved
where this fungicide was used as a single product for disease control. A
coordinated strategy of using the systemic fungicide, metalaxyl in
mixtures with protective multisite fungicides, such as chlorothalonil,
has been effective in slowing the development of resistance (Cooke, 1991;
Kadish et al., 1990).
Fosetyl al (Fosetyl aluminum) is another selectively active fungicide
against incipient infections of Phytophthora (GauUiard and Pelossier,
1983). It is applied to harvested citrus fruits to protect against and to
control Phytophthora spp., but it also reduces the incidence of green mold
(Penicillium digitatum) in storage (Eckert and Ogawa, 1985).
Among the fungicides that have proven efficient in controlling citrus
fruit decay, including infections by Geotrichum candidum, we have to
mention fenpropimorph and flutriafol. These compounds considerably
reduce the rate of rot, both in artificially inoculated lemons and in those
under natural infection conditions in the packinghouse. Their major
action is the suppression of contact-spread of the sour rot and the green
and blue molds following close contact with diseased fruit in the
container (Cohen, 1989).
Fungicides and fungistats, used for postharvest decay control, and
their chemical structures are given in Fig. 27. Detailed descriptions of
chemical compounds used for the control of postharvest diseases, and
their effect on disease development, are given in two comprehensive
reviews by Eckert and Ogawa (1985, 1988).
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