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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
18 Postharvest Diseases of Fruits and Vegetables
100 -f-
80
I 40
20 4-
Germ tube elongation
50 100 150 200 250 300
Resorcinols' concentration (ing/mr^)
Fig. 6. Effect of 5-substituted resorcinols on spore germination (o) and germtube
elongation (•) oiAlternaria alternata. Vertical bars indicate standard error
(Reproduced from Droby et al., 1986 with permission of Academic Press).
fungal suppression are greater than those naturally present in the fruit
(Swinburne, 1983).
The resistance of Bramley seedling apples to N. galligena has been
attributed to induced phytoalexin formation. Nectria invades wounds and
lenticels of apple fruits before harvest, but fruit rotting does not become
severe until after harvest.
The quiescence of Nectria in apples has been attributed to the
formation of benzoic acid in the necrotic tissue, following fungal
penetration into the fruit (Swinburne, 1978). The fungus resumes active
growth when the fruit ripens and the benzoic acid is decomposed
(Swinburne, 1983).
Some of the preformed compounds, such as the antifungal diene in
unripe avocado fruits, can be further induced in the host tissues.
Induction of higher concentrations of this compound was found in
response to challenge inoculation of unripe, but not of ripe fruit with C.
gloeosporioides.
The preformed antifungal substances naturally residing within the
host, the inducible preformed substances, and the phytoalexins formed as
a result of infection, and their role in host resistance, will be discussed
below in the chapter on Host Protection and Defense Mechanisms.
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