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

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FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE 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, http://arab2000.forumpro.fr
FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE 286 Postharvest Diseases of Fruits and Vegetables coupled with regular field spraying programs, also provides control of postharvest diseases of papaya (Alvarez and Nishijima, 1987). However, in the light of the sensitivity of various papaya cultivars to heat injury, a single hot dip (49°C for 15 min) was suggested as optimal for disease control with minimum effects on fruit quality (Nishijima, 1995). A hot water dip at 49°C for 20 min is effective in reducing early Rhizopus infections, mycelium being more sensitive to heating than fungal spores. Decay was further reduced and almost eliminated when a hot water treatment was coupled with fungicide field sprays. The main control measures against Rhizopus soft rot are, however, sanitation procedures. These include the removal of decaying fruit from areas around the packinghouse, and regular disinfestation of floors, packing lines and other packinghouse equipment and of bins used for transferring fruit from the field to the packer (Nishijima et al., 1990). Holding the fruit at 7-10°C will retard decay development during storage. AVOCADO The most significant postharvest diseases of avocado fruits are: anthracnose, caused by Colletotrichum gloeosporioides; fruit rot, caused by Dothiorella gregaria; and stem-end rots, caused by Botryodiplodia theobromae, Dothiorella gregaria, Alternaria spp. and Phomopsis spp. (Darvis, 1982; Muirhead et al., 1982). Other, less significant postharvest pathogens include Fusarium spp., Pestalotiopsis versicolor, Rhizopus stolonifer, Pseudocercospora purpurea, Trichothecium roseum, Penicillium spp., and the bacteria Erwinia carotovora and Pseudomonas syringae, 1. Colletotrichum gloeosporioides (Penz.) Sacc. (Perfect state: Glomerella cingulata (Stonem.) Spauld. & v. Schrenk) This fungus, which is responsible for anthracnose, may exhibit both the asexual state (acervuli and conidia) and the sexual state (perithecia and ascospores), but the asexual conidia play the main role in fungal infection. Initial infection of avocado peel takes place in the plantation during the growing season but, since avocados do not ripen on the tree, the infection remains quiescent in the immature fruits (Binyamini and Schiffmann-Nadel, 1972). Quiescence is exhibited by appressoria that are formed by germinating conidia and are located on the fruit surface, or by thin infection hyphae that penetrate under the cuticle or the external layers of the epidermis (Muirhead, 1981b; Prusky et al., 1990). Renewed http://arab2000.forumpro.fr
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