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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
278 Postharvest Diseases of Fruits and Vegetables
The benzimidazole compounds and imazalil applied to control the
wound pathogens of citrus fruit are not effective against Phytophthora,
On the other hand, metalaxyl is uniquely effective in eradicating
incipient infections of Phytophthora and has no effect on the development
of other postharvest diseases (Eckert and Ogawa, 1985). This compound
delayed the development of brown rot on citrus fruit (Cohen, 1981),
suppressed the growth of Phytophthora on the fruit and prevented
contact spread of the disease on inoculated grapefruit at 11°C. Later
studies (Ferrin and Kabashima, 1991) described the development of
metalaxyl-resistant isolates of P. parasitica as indicated by the increased
metalaxyl concentration needed for the suppression of mycelium growth
and of sporangia and chlamidospore formation. Fosetyl aluminum
applied after harvest was found to provide both protective and curative
action against P. parasitica infection (GauUiard and Pelossier, 1983).
Hot water dip treatments for 3 min at 46-49°C are effective in
eradicating Phytophthora infections when applied shortly after infection
(within a few days), while the fungus is still confined to the external
layers of the fruit peel where heat will penetrate rapidly (Klotz and
DeWolfe, 1961).
Disease control is dependent on careful handling and shipping of
strong, top-quality fruits and the avoidance of prolonged storage.
Harvesting of fruit at prime maturity can avoid the need for prolonged
degreening of the immature fruit with ethylene, which generally
increases fruit susceptibility to anthracnose. Preharvest ethephon
sprays, which promote fruit ripening with relatively small color changes
from green to yellow or orange, may allow the crop to be picked at prime
maturity and may also lead to triggering the resistance mechanisms of
the fruit (Barmore and Brown, G.E., 1978).
Suppression of citrus stem-end rots greatly depends on proper
refrigeration during storage and transportation, and temperatures
between 4 and 7°C are required to control these rots in transit.
However, for various citrus fruits, such as lemons, limes, grapefruits,
pomelos and certain hybrids, which are sensitive to low temperatures
and develop chilling injuries, higher temperatures should be
maintained. Since the minimum growth temperature of Colletotrichum
gloeosporioides is 9°C (Sommer, 1985), temperatures below 10°C would
delay the appearance of anthracnose symptoms. Storage temperatures
below 10°C also result in a very slow growth of the wound pathogen
G. candidurriy which has a high optimal growth temperature of 25-30''C
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