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

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Postharvest Disease Summary 317
by wet weather (Hewitt, 1974). The lesion is dark brown and firm and
the margins of the infected area are less distinct than those of
Cladosporium rot (Harvey and Pentzer, 1960).
D. Aspergillus niger v. Tieghem
This pathogen can be a serious problem when grapes are marketed at
ambient temperatures (Mandal and Dasgupta, 1983). The fungus
survives on plant debris in the soil at high temperatures (25-30°C) and
airborne spores infect berries via injuries caused by insect punctures,
splits and stem-end fractures. Infection occurs only in mature berries;
young berries are resistant to infection even when wounded (Abdelal et
al., 1980). Infection can also take place through injuries incurred during
handling. Since the fungus does not grow at temperatures below 5°C,
cold storage is effective in suppressing disease development (Matthee et
al., 1975).
E. Penicillium spp.
Several species of Penicillium, including P. citrinum Thom, P. cyclopium
West, and P. expansum Link, can infect harvested grapes causing the
blue mold rot (Barkai-Golan, 1974). Although infection can sometimes be
initiated before harvest, the disease is usually associated with wounds
and cracks in the skin at harvest (Harvey and Pentzer, 1960). Infection is
induced in injured berries by conidia, which are dispersed by air
currents, winds and insects. Decay continues to develop, although at a
very slow rate, during the prolonged cold storage of grapes at 0°C
(Harvey and Pentzer, 1960), and it may spread through the bunch.
F. Rhizopus stolonifer (Ehrenb. Ex Fr.) Lind and R. oryzae Went &
Prinsen Geerligs
Rhizopus rot, incited by both of these species, can become a problem
for grapes that are marketed at ambient temperatures (Mandal and
Dasgupta, 1983).
The fungi exist and sporulate in the soil and on plant debris. Asexual
spores (sporangiospores) are spread by air currents and primary infection
is via injuries (Barbetti, 1980). R, oryzae is also capable of penetrating the
intact skin of mature berries in the presence of exuded grape juice.
Infection continues to spread during storage, when rotted berries infect
adjacent healthy berries by contact. The infected tissue rapidly becomes
covered with sporangia (white when young, later turning black), which are
borne on sporangiophores that arise in clusters on the white mycelium.
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