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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
272 Postharvest Diseases of Fruits and Vegetables
temperatures for growth are 30°C for Diplodia and 23°C for Phomopsis
and Dothiorella. In general Phomopsis occurs throughout the harvest
season, whereas Diplodia is more common during the ethylenedegreening
season and in the late spring, when there are warmer
weather and frequent rains. Under humid conditions a superficial, fine
white mycelium may be developed on the Phomopsis-iniected fruits.
Surface growth is seldom seen on Diplodia-intected areas.
Alternaria citri is widely distributed in citrus-growing areas. Being
dispersed by wind and air currents in the grove, the conidia can be found
at the stem end, as well as on or underneath the 'button' of citrus fruits
of any age. In Navel oranges, fungal conidia may be located at the stylar
end (Singh and Khanna, 1966). However, infection may occur only if the
fruit has been injured or physiologically weakened by unfavorable
growing conditions. After harvest, infection may originate in peel injuries
or more frequently through the stem end, resulting in stem-end rotting.
Freshly harvested lemons, however, are resistant to Alternaria infection
while immature. Infection through the button occurs only at the
senescent stage, when the fungus is capable of progressing into the fruit,
affecting the central core and to some extent the inner tissues of the rind.
In this case, internal rot is frequently developed before the appearance of
external disease symptoms (Brown, G.E. and McCornack, 1972).
In oranges, grapefruits and some hybrids, the internal tissue becomes
black; hence the common name for Alternaria infection - the black rot
(Singh and Khanna, 1966). In Navel oranges, infection usually originates
at the stylar end. The ability of the fungus to penetrate the fruit through
senescent buttons may explain the prolonged prevalence of A, citri.
Similarly, citrus fruits that have been degreened by ethylene to
accelerate color development are liable to be infected by A, citri. Ethylene
treatment, by hastening senescence and thereby the death of the green
button, predisposes the fruit to invasion by stem-end fungi. In contrast,
the application of growth-regulating substances such as 2,4-D retards
senescence of the fruit button and delays disease initiation (Eckert and
Eaks, 1989).
3. Phytophthora spp.
Phytophthora citrophthora (Smith & Smith) Leon., Phytophthora
hibernalis Carne, Phytophthora nicotianae (van Breda de Haan)
var. parasitica (Dastur) Waterh. and other Phytophthora species are
the causal organisms of brown rot of citrus fruits.
Brown rot is a major fruit disease in all citrus growing areas and is
http://arab2000.forumpro.fr