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

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Postharvest Disease Summary 325
parasitica (Dastur) Waterh. and P. capsici Leonian (Snowdon, 1992).
These species are soil inhabitants and can survive in seeds as
thick-walled oospores (the sexual state) or chlamidospores. Infection
takes place in the field in warm, wet conditions, which favor the
production of thin-walled sporangia, the asexual state (Bhardwaj et al.,
1985) giving rise to numerous zoospores, which are swimming spores
that must have free water to survive and cause fruit infection. They are
capable of penetrating both unripe and ripe uninjured fruit. Infection is
generally confined to fruits growing low down on the plant, near to or in
contact with the soil (Springer and Johnston, 1982). When disease
development is interrupted by harvest, growth continues afterwards and
may be spread to healthy fruits by contact during storage.
In peppers, infection frequently originates at the stem end, whereas in
eggplants lesions often appear near the distal end. Phytophthora rot of
tomatoes is usually called TDuckeye rot' and is characterized by the
formation of concentric, brown rings around the point of disease
initiation. In humid conditions, an off-white mycelium, giving rise to
numerous sporangia, is developed on the surface of the infected area
(McColloch et al., 1982). The occurrence of the disease depends upon
weather conditions, regardless of geographical location.
I. Rhizoctonia solani Kuhn [perfect state: Thanatephorus
cucumeris (Frank) Donk]
This fungus causes soil rot or Rhizoctonia rot, which is of importance
mainly in tomatoes (Baker, K.F., 1970). Rhizoctonia is a soil-inhabiting
fungus, which produces both the sexual state (a hymenium giving rise to
basidiospores) and the sterile state (sclerotia). Infection occurs under wet
conditions by splashing of contaminated soil onto the low-hanging fruits
(Baker, K.F., 1970), but fruits in contact with the ground are generally
infected by penetration of the fungus from the soil through injuries
(Murphy et al., 1984). The disease develops on both green and ripe fruits
and is common in tomatoes intended for processing, since they are
generally grown without stakes and many of them remain in contact with
the soil until fully ripe. The rate of infection depends upon weather
conditions (McColloch et al., 1982): the optimal growth temperature is
26-27°C and there is little development below 10°C. Tomatoes that were
infected in the field but showed no evidence of decay, or were overlooked
during grading and packing, may decay during transit.
Typical spots on ripe fruits are firm and reddish brown, while the
infected flesh is soft or even watery. At an advanced stage of
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