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

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Postharvest Disease Summary 323
The infected tissue becomes soft and water-soaked and, later, the skin
may spht hberating an infecting liquid. Decay spreads rapidly from fruit
to fruit, forming nests of decay, especially under shelf-life conditions at
temperatures above 20°C. Keeping the fruits under refrigeration during
transport and storage suppresses bacterial growth.
D. Rhizopus stolonifer (Ehrenb. Ex Fr.) Lind
This species is the cause of Rhizopus rot, which can occur wherever
tomatoes, peppers and eggplants are grown. In tropical countries another
species, R. oryzae Went & Prinsen Geerligs, is common (Snowdon,
1992).
R. stolonifer is widely distributed in the soil and in the atmosphere and,
although it may produce sexual spores (zygospores), it commonly exists in
the asexual state as sporangia and sporangiospores. Spore germination
occurs in a warm, moist environment and penetration takes place via
injuries or damaged tissues (Barkai-Golan and Kopeliovitch, 1981). The
infected area of tomatoes and peppers appears water-soaked through the
distended skin, which often ruptures and releases an abundance of liquid.
Sporulation occurs on the surface of infected fruits and the disease is
spread to adjacent fruit, resulting in extensive 'nesting' during storage
(Barkai-Golan and Kopeliovitch, 1981). However, the disease develops
slowly in fruits stored at the recommended temperatures.
E. Geotrichum candidum Link ex Pers.
This fungus is responsible for the sour rot in stored tomatoes. It is a
soil-borne pathogen whose spores are transmitted mainly by insects.
Flies are known to transfer spores from rotten fruits to healthy fruits and
also to create wounds that enable fungal penetration (Butler, 1961). The
fungus is a wound pathogen, infecting both mature-green and ripe fruits
via the stem scar or any wound on the fruit surface. If fruits are infected
shortly before harvest, symptoms will not be visible at harvest and the
decay can develop during storage or marketing.
G. candidum has a high optimum growth temperature (about 30°C)
and can develop under warm, moist conditions. The infected tissues in
ripe fruits are soft and watery whereas those in mature-green fruits are
characteristically water soaked. In both cases decay is accompanied by a
sour odor. At an advanced stage, the infected skin splits and a
white-to-creamy mycelium begins to develop on the exposed tissue and
forms conidia (oidia or arthrospores) by fragmentation of the hyphae
(Butler, 1961).
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