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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Factors Affecting disease Development
buffering their environment in a range suitable for their growth and the
activity of their pectolytic enzymes (Bartz and Eckert, 1987).
2. GROWTH STIMULI
Certain compounds in the host tissues might, on certain occasions, affect
the host susceptibiUty to infection by stimulating pathogen growth.
Generally, spores o{ Penicillium digitatum do not germinate in water on the
surface of citrus fruit until the peel is injured (Smoot and Melvin, 1961).
However, when the peel is wounded, during harvesting or subsequent
handling and processing, P. digitatum spores germinate and their germ
tubes may penetrate the fruit, to initiate infection and, eventually, to
develop the typical green mold symptoms. Ascorbic acid and a number of
terpene compounds in citrus fruits, much hke their stimulating effect on the
germination of P. digitatum spores, can also stimulate mycehal growth of
this fungus, which is specific to citrus fruits (Pelser and Eckert, 1977;
French et al., 1978). Thus, the presence of citrus juice with the appropriate
acidity level can determine both the germination rate and the germ tube
growth and, in turn, the rate of fungal development and the incubation
period of the disease (Pelser and Eckert, 1977) (Fig. 9).
100
Fig. 9. Conidia germination and germ tube growth of Penicillium digitatim in
1% (v/v) orange juice dialysate at several pH values (Reproduced from Pelser
and Eckert, 1977 with permission of the American Phytopathological Society).
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