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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
260 Postharvest Diseases of Fruits and Vegetables
suspension culture indicated that salicylic acid may act as an
inhibitor of ethylene biosynthesis, by blocking the conversion of
1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene (Leslie and
Romani, 1986) and, therefore, may function as an inhibitor of fruit
ripening. Studies with tomato fruits showed that salicylic acid may
inhibit the increased expression of ACC gene, which is activated by fruit
wounding (Li et al., 1992). By functioning as an inhibitor of ethylene
production, salicylic acid would be able to enhance disease resistance
against pathogens that do not attack non-ripening tissues.
Antioxidants
Antioxidants are another class of compounds that can reduce
postharvest decay by modulating the natural fruit resistance. The
antifungal diene, which is responsible for the inhibition of Colletotrichum
gloeosporioides development in the young unripe avocado fruit, is
apparently oxidized by lipoxygenase during fruit ripening, allowing the
fungus to resume colonization of the fruit tissues. The activity of this
enzyme in the peel of ripening fruit is regulated by the natural antioxidant
epicatechin (Prusky and Keen, 1993). Laboratory studies showed that
infiltration or dip treatment of avocado fruit with several antioxidants,
such as a-tocopherol, butylated hydroxytoluene, butylated hydroxyanisole
and tert-hutyl hydroquinone, inhibited lipoxygenase activity, retarded the
decrease of the antifungal diene and, consequently, inhibited the
development of anthracnose (Prusky et al., 1985b). Following these findings
Prusky et al. (1995) showed that a dip or spray of avocado fruit (cvs. Hass
and Fuerte) with a commercial formulation of the antioxidant, butylated
hydroxyanisole (1200 iiig a.i. ml^) or the antioxidant combined with the
fungicide prochloraz (250 |xg a.i. ml-i) consistently reduced the incidence of
postharvest anthracnose caused by C. gloeosporioides in small and
semi-commercial experiments. The effect of the antioxidant plus prochloraz
lasted longer than that of the antioxidant alone, although prochloraz alone,
even at higher concentrations, did not always reduce decay incidence. It was
concluded that the antioxidant, which is a common food additive, prevented
the conversion of quiescent infections into active ones, a process associated
with fruit ripening and reduced resistance to infection.
3. BIOLOGICAL ELICITORS
The ability of various antagonistic microorganisms to act as
alternatives to systemic fungicides and control postharvest diseases may
be connected with their ability to produce and secrete antibiotic
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