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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
44 Postharvest Diseases of Fruits and Vegetables
Eckert and Ratnayake (1994) found that a mixture of limonene,
acetaldehyde, ethanol, CO2 and other volatile compounds emanating
from wounded oranges induced germination of P. digitatum conidia on
water agar. Fungal conidia that accumulate in water condensate on
citrus fruits can also be induced to germinate by volatile compounds
emanating from adjacent wounds. On the other hand, washing wounded
lemon fruit peel (epicarp) was found to greatly suppress P. digitatum
infection, when the fruit was inoculated with fungal spores, so that only
2% of the fruit showed green mold symptoms. However, when a
comparable amount of isolated lemon peel oil was topically applied to the
washed wounds, 92% of the inoculated wound sites did develop complete
green mold symptoms (Arimoto et al., 1995).
In the light of the finding that peel oil extracts applied to wounded
epicarps can restore disease development potential to the pathogen,
Arimoto et al. (1995) investigated the possibility that some components of
the lemon peel oil might be essential for fungal development in the peel
tissues. These studies indicated that lemon epicarp oil, with the limonene
removed, promoted the production of green mold symptoms on only 28%
of the wounds, suggesting that limonene was one facilitator of green mold
formation on wounded fruits. However, another promoting factor was
isolated from the oil and was identified as prangolarin by spectrometric
analysis. Prangolarin by itself enhanced P. digitatum development on
wounded epicarps of lemons, resulting in the development of green mold
symptoms because of the production of masses of conidiophores and
conidia (Arimoto et al., 1995).
In potato tubers a close connection was found between the reducing
sugar content and the susceptibility of the tuber to bacterial soft rot
during storage at various temperatures (Otazu and Secor, 1981). A
correlation was also found between the sugar contents of nectarine and
plum fruits and their susceptibility to Botrytis cinerea infection (Fourie
and Holz, 1998); this finding will be discussed below in regard to
enhanced susceptibility to decay during the ripening stage. Edlich et al.
(1989) found that certain sugars taken up by B. cinerea could stimulate
fungal growth and enhance its infection capability, but suggested that
the stimulation was due to the active oxygen formed rather than to a
nutritional effect. Pollen exudates from weeds commonly found in stone
fruit orchards have also been found to be stimulators of J3. cinerea growth
(Fourie and Holz, 1998). When added to the fungus conidia during the 4
weeks prior to the picking-ripe stage the exudates significantly increased
the aggressiveness of the pathogen on plum and nectarine fruits. The
http://arab2000.forumpro.fr