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

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Postharvest Disease Summary 299
and Fourie, 1984) or via the stem end (Lopatecki and Peters, 1972). In
some apple cultivars, penetration occurs through the open calyx tube
(Sharpies and Hims, 1986; Spotts et al., 1988) resulting in core rot.
Although the susceptibility of apple cultivars to M piriformis may differ
among different locations or different years, Granny Smith and Braeburn
have generally been found to be the most susceptible cultivars and Royal
Gala the most resistant one to Mucor infection (Spotts et al., 1999).
Fruits with unseen initial infection may be introduced into the storeroom
where fungal development proceeds even at 0°C (Lopatecki and Peters,
1972). According to the site of fungal penetration, lesions may appear on
the fruit surface (Combrink and Fourie, 1984), at the stem end
(Lopatecki and Peters, 1972), or in the core region (Spotts et al., 1988).
The rot is soft and watery, and under humid conditions is
characterized by the appearance of minute black heads, which are the
sporangia of the fungus. It differs from Rhizopus watery rot in its lack of
a sour odor (Combrink and Fourie, 1984).
J. Rhizopus spp.
Rhizopus stolonifer (Ehrenb. ex Fr.) Lind and, to a lesser extent,
Rhizopus oryzae Went & Prinsen Geerligs, are the cause of Rhizopus rot
of pome fruits. However, while Rhizopus rot is a serious postharvest
disease of stone fruits, it is not considered a major disease of pome fruits.
Infection is initiated by the asexual spores (sporangiospores), which
are common components of the air spora (Barkai-Golan et al., 1977b).
The rot is soft and watery and, at its progressive stage, releases juices
having a sour odor. The sexual state (zygospores) has rarely been
reported. The fungus is heterothallic and requires the presence of two
physiologically different and compatible mycelia for sexual reproduction
(Alexopoulos, 1961). The development of both species of Rhizopus is
inhibited at temperatures below 5°C and the rot is, therefore, prevented
at the storage temperatures recommended for apples.
K. Alternaria alternata (Fr.) Keissler
This fungus is the main cause of Alternaria rot in pome fruits. Infection
is initiated by conidia that are produced in abundance on leaf debris and
other plant material in the orchard. The conidia, which are very important
components of the air spora (Barkai-Golan et al., 1977b), are disseminated
by wind and rain, and are generally present on the fruit surface at harvest
time. The fungus is a weak pathogen that frequently colonizes damaged or
senescent fruit. Several different symptoms can be produced following
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