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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
13 8 Postharvest Diseases of Fruits and Vegetables
delayed aging of the stem-end button, which is the usual point of attack
by the stem-end fungi, resulting in considerable reduction of stem-end rot
(Schiffmann-Nadel et al., 1972). The pathogenic fungi lodge in the
button area in a quiescent state, and the delayed dropping of the button
from the fruit which results from 2,4-D treatment delays their transition
to the active state, so retarding decay development. The effectiveness of
2,4-D in preserving green buttons and suppressing decay development,
has been proven both by using preharvest spraying in the orchards and
by postharvest treatment by dipping the fruits in aqueous solutions of
2,4-D or of waxes containing 2,4-D (Stewart, 1949; Schiffmann-Nadel et
al., 1972). Most lemons grown in California are treated with 2,4-D before
storage to delay senescence of the button, and a wax formation
containing 2,4-D is applied to various citrus cultivars in South Africa and
Israel, to control stem-end rot during long-distance shipment and
prolonged storage (Ben-Arie and Lurie, 1986).
Gibberelins, which are hormones found naturally in plant tissue, may
also function in a similar way. The increased susceptibility of citrus fruits
to Penicillium digitatum and P. italicum, as they become physiologically
older, may be due to the reduction in resistance to fungal entry as well as
to an improvement of the rind as a medium for the pathogen growth.
Gibberelic acid (GA3) application delayed the senescence of the rind of
Navel oranges, as exhibited by softening, the appearance of intercellular
spaces, weakened or broken cell walls and increased fruit resistance to
infection (Coggins and Lewis, 1965).
A more recent study (Ben-Yehoshua et al., 1995) indicated that
dipping lemon fruits in GA3 (50 or 100 ppm) or in 2,4-D (200 ppm) prior
to storage retards the decrease in the antifungal citral compound in the
fruit rind (the flavedo), suppresses the antifungal activity of the rind and
results in reduced decay during storage. The inhibition of the
decomposition of the antifungal compounds in the rind is the basis of the
mode of action of the growth regulators in decreasing decay in the
harvested lemon fruit.
Pre-harvest sprays with GA3 (20 mg ml^) applied during the
development of persimmon fruits were effective in reducing decay caused
by the black spot disease (Alternaria alternata)^ which typically appears
in the high humidity environment beneath the calyx in stored persimmon
fruits (Perez et al., 1995). As a result of GAs treatment, the calyx of the
fruit remained erect until harvest and fruit softening was inhibited, and
in parallel, the fruit area covered with the black spot was markedly
reduced during 3 months of storage at O'^C. The plant hormone had no
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