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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
306 Postharvest Diseases of Fruits and Vegetables
tubes may give rise to appressoria when they have reached lengths of
10-15 |am. Thin infection hyphae (or infection pegs) formed from the
inner appressorium wall enter the substomatal cavity of the fruit via
stomata. In the green fruit no further fungal growth occurs, probably
because of resistance reactions characteristic of young tissue, such as
the presence of preformed phenolic compounds or callose at the site of
infection (Fourie and Holz, 1995). When nectarines are invaded by
B, cinerea at an advanced stage of fruit maturity (near the picking-ripe
stage), the majority of infection hyphae do penetrate the cuticle. In
plum fruits at this stage of maturity, only a small number of successful
penetrations have been recorded. In both nectarines and plums,
however, susceptibility to infection increases with fruit maturity.
Enhanced infection in mature nectarine fruits can also result from the
appearance of cuticular micro-cracks on the fruit surface. These can
provide alternative penetration routes for the pathogen (Fourie and
Holz, 1995). The fruit can also be invaded via injuries sustained during
harvesting and handling.
The gray mold rot is soft and, under humid conditions, produces
abundant surface mycelium. Under dryer conditions sporulation is
prolific and a mass of gray conidia are formed, which constitute a ready
source for initiation of new infections.
C. Rhizopus spp.
Rhizopus stolonifer (Ehrenb. ex. Fr.) Lind and Rhizopus oryzae Went &
Prinsen Geerligs cause Rhizopus rot, one of the most serious postharvest
diseases of stone fruits (Hall and Scott, 1989b). It inflicts heavy losses,
especially in peaches, nectarines and cherries. Rhizopus spp. exist on dead
material and their asexual spores (sporangiospores) are disseminated in
the air where they form important components of the air spora and are
responsible for disease initiation. The fungi generally infect the fruit via
injuries sustained during harvesting and handling. Infected areas are
water-soaked and covered with a profuse white mycelium which gives rise
to globular sporangia with new sporangiospores. The fruit becomes very
soft and, at the progressive stage of the disease, releases juices having a
sour odor. During storage a rotted fruit infects sound fruit by contact (Hall
and Scott, 1989b), causing extensive 'nesting'.
The fungi tolerate high temperatures, having optima of 25°C for
R. stolonifer and 35°C for R, oryzae, and infection is favored by a warm,
moist environment (Pierson, 1966).
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