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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
90 Postharvest Diseases of Fruits and Vegetables
directly with the inducement of these compounds at the wound site. It
was further found that dipping the fruits in the non-toxic compound,
potassium phosphonate, increased the resistance of the wound to
P. digitatum infection (Wild, 1993). This was only noticeable when at
least 24 h was allowed between dipping the freshly wounded fruits and
inoculating them with Penicillium spores. Since this compound has no
direct effect on Penicillium growth in vitro, it was concluded that the
potassium phosphonate was eliciting enhanced production of these
antifungal compounds in the host, and this conclusion was further
supported by the finding that cycloheximide, which is a protein synthesis
inhibitor, negated the effect of the phosphonate (Wild, 1993).
Studies with young apricot fruits indicated that the mechanical
barrier formed in response to fungal penetration may also prevent
reactivation of a quiescent infection. The cell-wall suberization of living
cells surrounding the infection point of Monilinia fructicola in the young
fruit and the accompanying accumulation of phenolic compounds, have
been hypothesized to be the reason for the non-activation of the quiescent
fungus growth (Wade and Cruickshank, 1992). When the fruit ripens,
however, viable hyphae of M fructicola may escape from the arrested
lesions and cause fruit decay. Curing effects and decreased incidence of
Botrytis cinerea can be obtained in kiwifruit by prolonging the time
between harvesting and cool storage (Pennycook and Manning, 1992). In
determining the critical conditions required during curing of kiwifruit in
order to minimize Botrytis rot during storage, Bautista-Bafios et al.
(1997) concluded that temperatures between 10 and 20°C, together with
relative humidity (RH) higher than 92% for a three-day curing period,
should provide adequate disease control without lowering fruit quality
during cold storage (0°C); increased temperature or decreased RH
generally resulted in increased fruit weight loss.
F. ACTIVE OXYGEN
Active oxygen, produced by plant cells during interactions with
potential pathogens and in response to elicitors, has recently been
suggested to be involved in pathogenesis. "Active oxygen species",
including superoxide, hydrogen peroxide and hydroxyl radical, can affect
many cellular processes involved in plant-pathogen interactions (Baker
and Orlandi, 1995). The direct antimicrobial effect of active oxygen
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