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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Factors Affecting disease Development 41
within the package, which results from extreme changes in the storage
and shipping temperatures. Perforating the hning is of primary
importance, since the holes allow limited vapor emission, with acceptable
weight loss (with no visible shriveling), prevent ethylene accumulation in
the herbal atmosphere, and protect the leaves from decay (Aharoni, 1994).
Many fruits and vegetables are more susceptible to the pathogen when
their tissues are in a turgid state through being under high RH. In many
cases, the increased decay rate should be attributed to moisture held
within the wounds, lenticels or stomata under these conditions. Fungal
spores use this moisture when germinating, prior to their penetration
into the tissues. Crops such as apples and pears, with well developed
cuticle and epidermal layers, tolerate relatively lower RH levels, which
helps to prevent storage decay due to the inhibition of fungal spore
germination (Spotts and Peters, 1982b). However, when Anjou pears were
wounded prior to inoculation, spores of some of the important pathogens,
such as Botrytis cinerea and Penicillium expansum, did germinate and
cause decay at 97% RH in cold storage (-l.l^C). It is well known that
accumulated water drops on the surface of citrus fruits stimulate the
development of the green mold (Penicillium digitatum). Therefore, slightly
drying the fruit might reduce its susceptibility to decay (Eckert, 1978).
The water content of host tissues (water status) is a major
contributing factor in the development of soft rot bacteria. In various
vegetables, such as bell peppers and Chinese cabbage, high water status
has frequently been associated with high potentials for bacterial soft rot
(Bartz and Eckert, 1987). Accumulation of free water on potatoes stored
in a relative humidity of over 95% and at a low temperature increases
the rate of soft rot caused by bacterial penetration through the lenticels.
Ventilated storage rooms and dried-up tubers can, therefore, reduce the
bacterial decay (Perombelon and Lowe, 1975). On the other hand,
Botrytis and Rhizopus easily attack carrots that have commenced
withering and have lost over 8% of their water volume (Thorne, 1972).
The increased susceptibility of the carrot under these conditions is
attributed to the cell separation and enlargement of the intercellular
spaces, which accompany the dehydration.
Studies conducted by van den Berg and Lentz (1973, 1978) found that
the decay rates in cabbages, Chinese cabbages, cauliflowers, carrots, celery
and other vegetables, in cold storage with relative humidity of 98-100%,
were no higher than those under lower relative humidity, and at times
were even lower. Under hyper-humidity, the firmness and freshness of
vegetables were preserved much longer, and the pectolytic action of the
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