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

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FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE Physical Means 211 sufficient to reduce Colletotrichum decay significantly, but not Thielaviopsis decay. The reduction of anthracnose was probably the result of ripening inhibition, while higher doses caused darkening of the peel, that increased with the dose (Alabastro et al., 1978). Irradiation is mostly effective in delaying senescence in potatoes and onions, the delay being typically expressed by the inhibition of sprouting during storage (photos 3 and 4). Because of its action on the meiosis in the meristematic area of these crops, irradiation may delay sprouting at doses as low as 50-150 Gy or even less (Thomas, 1983, 1984). Gamma irradiation at 60 Gy has similarly been found effective in preventing sprouting and rooting of fresh ginger rhizomes held at ambient temperatures (Mukherjee et al., 1995). However, in contrast to fruits, in which ripening and senescence delay is accompanied by decay suppression, potato or onion irradiation at sprout-inhibiting doses may result in enhanced susceptibility to storage pathogens. In order to prevent significantly increased decay in irradiated onions and garlic, healthy, good-quality bulbs should be used; they should be irradiated during the dormancy period; and good storage management should be practiced (Thomas, 1984). El-Sayed (1978) reported that the phs^toalexins, rishitin and lubimin formed in potato tubers, and rishitin formed in tomato fruits, in response to infection were reduced after gamma irradiation. In parallel, increased incidence of rotted tubers and fruits was frequently reported after exposure to the radiation doses required for potato sprout inhibition (100 Gy) and for tomato fruit shelf-life extension (3 kGy). Post-irradiation treatment of tubers and fruits with phytoalexins produced by members of the Solanaceae, contributed to the control of microbial spoilage (El-Sayed, 1978). Irradiating carrots at a sprout-inhibiting dose (120 Gy) generally results in increased decay during prolonged storage (6 months at 2°C and 95-100% relative humidity). However, irradiation seems to contribute to decay suppression for short-term storage of carrots (Skou, 1977). Electron irradiation (P rays) apphed only to the top ends of carrots prevented sprouting for 6 months, without increasing the incidence of rot (Skou, 1977). Combined Treatments Treatments that combine radiation with other control means, physical, chemical or biological, were developed in an attempt to reduce the radiation doses required for disease control to beneath the damage threshold of the fruit or vegetable. Among the combined treatments, special attention has been drawn to heat-plus-radiation combinations. http://arab2000.forumpro.fr
FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE 212 Postharvest Diseases of Fruits and Vegetables Hot water dips and gamma radiation were found to react synergistically on spore inactivation of various postharvest fungi (Barkai-Golan et al., 1977a) permitting the use of a lower level of each of the treatments than when it was applied separately. In most cases the combined treatment is more effective when the hot water dip proceeds the irradiation (Sommer et al., 1967) (Fig. 35); the exposure of spores to high temperatures sensitizes them to radiation. As well as conferring the advantage of the synergistic effect of the two physical means, the combined treatment markedly delays decay development in many fruits, such as citrus, papaya, mango, plum and nectarine (Barkai-Golan, 1992). 1 2 3 4 1 2 3 4 The treatment Fig. 35. Survival of conidia after heat treatment and irradiation. 1 = irradiation alone, 2 = heat only, 3 = irradiation followed by heat, 4 = heat followed by irradiation: (A) Botrytis cinerea subjected to 44°C for 4 min or a 75-krad dose, or both; (B) Penicillium expansum subjected to 56°C for 4 min or a 20-krad dose, or both. Vertical lines indicate standard deviations (Reproduced from Sommer et al., 1967 with permission of the American Phytopathological Society). http://arab2000.forumpro.fr
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