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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
12 Postharvest Diseases of Fruits and Vegetables
Penetration of the various Phytophthora species into the host, in the
field or in the orchard, is not hnked with a typical quiescent infection
wherein the pathogen development ceases following its penetration into
the tissues or at an earlier stage. The principle concerning this fungus is
that the harvest ends its development within the host while the latter is
still on the parent plant, thus causing the decay to occur after harvest or
during storage.
In many vegetables, such as carrot, cucumber, lettuce, celery, cabbage,
cauliflower and others, a soft watery decay caused by Sclerotinia
sclerotiorum is common. This fungus, common in the soil, and especially
in heavy soil, might attack the vegetable when still in the field or during
harvest and continue to develop in its tissues throughout storage or
marketing.
Quiescent or Latent Infections
The fungi that penetrate into the host in the field also include
pathogens that cause latent or quiescent infection. These pathogens reach
fruits or vegetables that are still on the parent plant. However, during
one of the phases between their reaching the host and the development of
progressive disease, their growth is arrested until after the harvest,
when physiological and biochemical changes occurring within the host
will enable their renewed growth. Verhoeff (1974) has described such
arrested infections as "latent infections". However, since this term has
been used for describing different phenomena in various areas, it was
later suggested by Swinburne (1983) to leave the term "latent infection"
for wider uses and adopt "quiescent infection" for cases in which the
pathogen growth is temporarily inhibited. In some instances we find that
the inactive state is termed 'latent' if not visible to the eye and 'quiescent'
if visible (Smilanick, 1994), while in others the two terms are frequently
used to describe the same phenomenon. Jarvis (1994) believes that the
latent state of the pathogen, whether involving spores that have landed
on the host surface, spores that have commenced germinating, or
primary hyphal development within the host tissues, is linked to a
dynamic balance among the host, the pathogen and the environment.
The physiological and biochemical changes occurring in the host tissues
after harvest and during storage might affect the pathogen, the host and
their interrelationships and lead to the activation of the latent pathogen.
The gray mold, which is the main cause of decay in harvested
strawberries, is an example of disease originating in a quiescent infection
with Botrytis cinerea that is acquired in the field. The Botrytis spores.
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