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

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Postharvest Disease Summary 321
and E. carotovora (McColloch et al., 1982), which are characterized by
high optimal growth temperatures. Other pathogens may be of local or
occasional importance. Various fungi, such as Trichothecium roseum and
species of Phomopsis, Colletotrichum, Phoma, Pythium, Sclerotinia,
Stemphylium, Cladosporium, Penicillium or Aspergillus, may also be
involved in fruit decay but are considered of minor importance.
A. Botrytis cinerea Pers. [perfect state: Botryotinia fuckeliana (de
Bary) Whetzel]
This fungus is generally regarded as the major pathogen in
greenhouse-grown tomatoes and peppers, while Alternaria is of greater
importance in field-grown crops (Dennis, 1983b). B. cinerea can persist in
the soil or on plant debris as sclerotia and, under cool, moist conditions,
it produces an abundance of asexual spores (conidia) which are dispersed
by air currents. The pathogen can penetrate young fruits through
senescent flower parts (Lavy-Meir et al., 1988), through growth cracks
and wounds or via the stem end, before or during harvesting. However, if
the fruits are weakened by exposure to chilling in the field or during
storage, they become susceptible to direct penetration, and lesions may
develop anywhere on their surface (McColloch et al., 1982). In addition to
penetrating chill-injured fruit, the fungus can directly penetrate the
cuticle of immature fruit but, in this case, further growth is arrested and
*ghost spots' are formed on the growing fruit (Verhoeff, 1974).
The infected tissue is soft and water-soaked. Under humid conditions,
an abundance of gray-brown conidia, sometimes accompanied by black
sclerotia, are formed and serve as inoculum for new infections.
A considerable proportion of the rots caused by B. cinerea spread during
storage by contact between infected and sound fruits.
B. Alternaria alternata (Fr.) Keissler
This is a very common pathogen of solanaceous fruits (Barkai-Golan,
1981), which can limit their commercial life after harvest. The fungus
survives on plant debris and its conidia are very important components
of the air spora.
Alternaria is a weak pathogen that requires injured or weakened
tissue for penetration and development. When free water forms on the
surface of ripening fruit from rain, dew or overhead irrigation, spores
germinate in response to water-soluble nutrients on the fruit surface
(Pearson and Hall, 1975). The fungus can enter via growth cracks, insect
injuries or mechanical damage, but infection is often initiated at the
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