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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
62 Postharvest Diseases of Fruits and Vegetables
(1) The inducement of disease symptoms by the isolated toxin;
(2) Demonstration of the presence of the toxin within the diseased
host;
(3) Demonstration of a correlation between the rate of toxin
production in vitro and the pathogenicity of the isolate within the
host;
(4) A correlation between disease susceptibility and toxin sensitivity.
Although this is the main criterion for host-specific toxins, it may
also be applicable to some non-host-specific toxins at the cultivar
level, e.g., tenuazonic acid from Alternaria alternata or the raw
toxin solution from Fusarium moniliforme;
(5) Indications of the role of toxins during pathogenesis can be
obtained when their activity in vivo is inhibited within the host or
by specific environmental conditions, and these manipulations
result in suppression of disease development.
Examples of non-host-specific fungal toxins that have a role in disease
development, or have been suggested to be involved in disease, are
produced by fungi that may be responsible for postharvest diseases. They
include: fumaric acid, produced by Rhizopus species; oxalic acid,
produced by Sclerotium rolfsii and Sclerotinia sclerotiorum; ophiobolins
produced by Helminthosporium species; fusaric acid produced by
Fusarium oxysporum; malformin produced by Aspergillus niger;
coUetotrichins produced by Colletotrichum species; and tentoxin
produced by A alternata f. tenuis (Macko, 1983; Scheffer, 1983). In fact,
most Alternaria species may produce non-host-specific toxins, which are
not prerequisite for infection.
A. alternata, one of the most common postharvest pathogens of various
fruits and vegetables (Barkai-Golan, 1981), has been reported to produce
several toxic compounds in harvested fruits. Stinson et al. (1981)
reported that the major toxin produced in tomato fruits was tenuazonic
acid, with a maximal concentration in tomato tissue of 13.9mg/100g;
alternariol, alternariol monomethyl ether, and altenuene were produced
in much smaller amounts. The major toxins recorded in apples were
alternariol and alternariol monomethyl ether, with maximum
concentrations in tissue of 5.8 and 0.23mg/100g, respectively. Inoculation
of oranges and lemons with the same fungal isolate showed that the
predominant toxins in these hosts were tenuazonic acid, alternariol
monomethyl ether and alternariol, with concentrations in tissue of only
2.66, 1,31 and 1.15mg/100g, respectively. Working with another strain of
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