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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
312 Postharvest Diseases of Fruits and Vegetables
and raspberries can arise, either from germination of spores on the
surface of the fruit or from renewed growth of the quiescent infection
that had been initiated in the field. Davis and Dennis (1979) found that
the majority of strawberry infections occurring during storage appear on
the surface of the fruit and only a small proportion are initiated from
quiescent infections at the stem-end. Sporulation on diseased flowers and
fruits becomes an important source of secondary inocula in annual
production systems where flowers are continuously produced over several
months (Legard et al., 2000).
The decay is brown and firm, and its surface becomes covered with an
abundance of conidiophores bearing gray-brown conidia. Under humid
conditions, a white to gray mycelium with only a few spores
characteristically grows over the lesions (Dennis, 1983a). Sclerotia are
rarely found, and their development is dependent on Botrytis strains or
isolates and environmental conditions. Having a minimal growth
temperature of about -2°C, the gray mold is capable of development even
at the low temperatures used for storage (Dennis and Cohen, 1976). The
decay can spread readily by contact between rotten and healthy fruits,
causing 'nesting' during storage (Sommer et al., 1973). Rapid reduction of
the temperature from the field level to 1°C, and low-temperature storage
can only delay fungal development.
B. Rhizopus spp. and Mucor spp.
These fungi are responsible for the "leak" disease, a destructive soft
watery disease of soft fruits. The Mucor species involved are M piriformis
Fischer and, occasionally, M hiemalis Wehmer. The Rhizopus species are
R. stolonifer (Ehrenb. ex Fr.) Lind, a heterothallic species (requiring the
presence of two physiologically compatible mycelia for sexual reproduction),
and in some areas R, sexualis (Smith) Callen, a homothallic species
(having a self-fertile mycelium).
Mucor and Rhizopus are soil inhabitants but, unlike Botrytis, they do
not sporulate on plant debris in the field. Sporulation usually occurs only
on infected ripe fruits. The soil-borne inocula of the two fungi cause
limited early infection in the plantation. After being established in ripe
fruits the inoculum level increases and the latter part of the season is
characterized by enhanced contamination and higher rates of infection by
these fungi (Dennis, 1978). Infection is initated by the asexual spores
(sporangiospores). Germination of sexual spores (zygospores) of i?. stolonifer
has been observed only rarely (Alexopoulos, 1961), while those of
http://arab2000.forumpro.fr