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

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Postharvest Disease Summary 285
weather, are capable of infecting uninjured papaya fruits. Infected fruits
fall to the ground and serve as a source of new infections in developing
fruits (Srivastava and Tandon, 1971). Invasion may, however, occur at
the cut stem and result in stem-end rot development (Alvarez and
Nishijima, 1987).
4. Rhizopus stolonifer (Ehrenb. Ex Fr.) Lind
Rhizopus rot, caused by Rhizopus stolonifer, is a destructive rot of
papaya. Spores of the fungus are ubiquitous and infection originates only
via injuries inflicted during harvesting and handling. Severe problems
occur particularly during extended rainy periods (Nishijima et al., 1990).
The fungus infects mature fruits, causing a soft watery rot. Under
warm humid conditions, a loose white mycelium bearing black sporangia
(giving rise to sporangiospores) is being developed. Infected fruits, which
rapidly collapse, cause contact infection of neighboring fruits during
shipment and storage (Quimio et al., 1975). Nishijima et al. (1990) found
that the optimum temperature for disease development was about 25°C
and that no disease developed at 5 or 35°C; they also showed that the
fungus is consistently capable of infecting the fruit through lesions
caused by Colletotrichum gloeosporioides, Phomopsis sp. or Cercospora sp.
Control Measures
Postharvest diseases of papaya are controlled by frequent fungicide
sprays in the plantation followed by postharvest hot water and fungicide
treatments (Eckert, 1990). The frequent fungicide sprays in the
plantation control quiescent infections of Colletotrichum and incipient
infections of Phytophthora, and reduce the inoculum levels of Phoma
(Mycosphaerella), Botryodiplodia and other pathogens that invade the
fruit through wounds (Alvarez et al., 1977; Bolkan et al., 1976). The
traditional treatment of hot water at 48°C for 20 min was used in Hawaii
for many years to control anthracnose, stem-end rots and incipient
Phytophthora infections (Akamine, 1976; Aragaki et al., 1981). However,
this treatment delayed color development and caused a slight heat
injury, accompanied by an increase in Stemphylium infection (Glazener
and Couey, 1984). A combination of shorter, hotter water sprays (54°C
for 3 min) followed by a fungicide treatment, was recommended for
papayas destined for long distance shipment (Couey and Alvarez, 1984).
In order to satisfy the quarantine requirements for eradication of fruit
flies in papaya shipments to fly-free zones, the double hot water dip (30
min at 42°C followed by 20 min at 49''C) was adopted. This treatment,
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