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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
298 Postharvest Diseases of Fruits and Vegetables
G. Phytophthora cactorum (Lebert & Cohn) Schroet. and
Phytophthora syringae (Kleb.) Kleb.
These two species, which are the causal pathogens of Phytophthora rot,
are soil-borne. Infection is closely related to rainfall which splashes infected
soil onto fruits close to the ground (Edney, 1978). The asexual spores
(zoospores), which are the main agents of infection, come into contact with
low-hanging fruits and generally infect them via the lenticels. This process
requires free water or wetness (Edney, 1978). Fallen apple and pear leaves
have also been found to bear the sexual state of Phytophthora (oospores)
and are considered to be an important source of inoculum in the orchard
(Harris, 1979). After a resting period, and under wet conditions, the
oospores germinate to form sporangia that release new zoospores. Fruit
harvested in the early stages of disease development undergo rotting later,
in storage. Decay is spread during storage by contact of infected fruit
with sound fruit, forming 'nests' of decayed fruit (Edney, 1978).
H. Botryosphaeria spp.
Two species are responsible for apple and pear rots (Combrink et al.,
1984; Brown, E.A. and Britton, 1986): Botryosphaeria obtusa (Schw.)
Shoem (imperfect state: Sphaeropsis sp.) and Botryosphaeria ribis
Grossenb. & Duggar (imperfect state: Dothiorella sp.).
JB. obtusa [syn. Physalospora obtusa (Schw.) Cooke], the cause of the
black rot, and B. ribis, the cause of the white rot, may both produce the
asexual state (pycnidia with conidia) and the sexual state (perithecia
with ascospores). The conidia are water-borne while the ascospores may
be dispersed to greater distances by air currents (Snowdon, 1990). Both
stages are capable of producing the disease. The fungi may penetrate into
the fruit via lenticels, bruises, or cracks, while in the orchard, in transit
or in storage. Young fruits are resistant to rotting (Sitterly and Shay,
1960), becoming susceptible on maturation. Thus, fruit harvested shortly
after infection will rot later in storage.
Symptoms may vary with the temperature but both fungi can be
controlled during storage at about 0°C.
I. Mucor piriformis Fischer
Mucor rot can develop on various cultivars of pears and apples. The
fungus in the sexual state, as zoospores, can survive hot dry periods
(Michaelides and Spotts, 1986), while the asexual state (sporangia with
sporangiospores) is of prime importance in the fungal infection. The
fungus may penetrate the fruit through injuries of the skin (Combrink
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