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

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FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE Means for Maintaining Host Resistance 141 GAs on fungal and bacterial growth in vitro has been recorded, and its effect on the development of pathogens has been attributed to maintaining the decay resistance of the fresh celery heads. Dipping harvested celery heads in GA3 solution with TBZ and chlorine served for many years in Israel as a standard treatment in celery intended for export. A recent study showed that spraying the fields with GA3 before harvest delayed the natural decrease in the antifungal compound marmesin (Afek et al., 1995a). Maintenance of the high level of marmesin in the petiole tissues after harvest was suggested to be the mode of action by which the plant hormones inhibit decay development in stored celery. Delay of deterioration by the synthetic auxin, h-naphthalene acetic acid (NAA) was studied in eggplants (Temkin-Gorodeiski et al., 1993). Eggplant fruits deteriorate during prolonged storage, mainly because of accelerated senescence of the calyx, which precedes deterioration of the fruit. Dipping the calyx in NAA solution (200 ppm) maintained calyx freshness, which is an important aspect of the appearance of the fruit, but it did not prevent decay development. The addition of the fungicide prochloraz (900 ppm) retarded both calyx senescence and decay development, caused mainly by A. alternata, and kept the fruit firm. Dipping the whole fruit gave even better results and the residual level of prochloraz in such fruits was less than 0.34 mg T^, which is lower than the maximal level approved by the authorities in Europe. A triple combination of NAA, fungicide solution (Prochloraz, 900 mg l-i active ingredient) and bulk packaging in polyethylene-lined bags with water-absorbent materials, prevented water condensation and maintained eggplant quality along with reduced incidence of decayed fruit during storage (Fallik et al., 1994b). The higher levels of CO2 obtained within the bags (1.2%) may have partially contributed indirectly to the inhibition of decay development, by delaying fruit senescence. Such a combination could considerably expand the export potential of high-quality fruit (Fallik et al., 1994b). The use of auxins is limited since, in high concentrations, these compounds might accelerate ethylene production and thus enhance the aging process. In general, plant growth regulators may be of special importance mainly for fruits and vegetables that cannot be stored at low temperatures because of their cold sensitivity, as well as in developing countries where cold storage cannot be applied. http://arab2000.forumpro.fr
FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE 142 Postharvest Diseases of Fruits and Vegetables D. CALCIUM APPLICATION Another means of suppressing storage disease by maintaining or enhancing the natural resistance of fruits and vegetables to pathogens, is to increase the calcium content of the various plant organs (Conway et al., 1994b). Calcium is an essential element which influences the growth and fruiting of plants and contributes to preserving the structural integrity and functionality of membranes and the cell wall during fruit ripening and senescence. Calcium treatments applied to improve fruit and vegetable quality have primarily addressed the association of low calcium content in plant tissue with the development of physiological disorders. Calcium treatment may reduce storage disorders, such as bitter pit and internal breakdown in apples (Bangerth et al., 1972; Reid and Padfield, 1975) or the internal brown spot in potato tubers (Tzeng et al., 1986). However, many reports have indicated that an increase in tissue calcium content also led to reductions in fungal and bacterial decay. It was thus found that pre-harvest calcium sprays reduced the rate of storage losses caused by Gloeosporium spp. in apples (Sharpies and Johnson, 1977), or Botrytis and Geotrichum rots in stored grapes (Miceli et al., 1999), while postharvest calcium treatments reduced the rate of the blue mold disease caused by Penicillium expansum in this fruit (Conway and Sams, 1983). Similarly, bacterial soft rot caused by Erwinia carotovora pv. atroseptica in potato tubers decreased as tissue calcium increased (McGuire and Kelman, 1984). Various methods for increasing the calcium concentration in storage organs have been investigated. Applying Ca to harvested fruit seems to be the best method for increasing the calcium content in apples; active infiltration procedures with CaCb solution, such as vacuum or pressure that force solutions into the fruits, were more effective in reducing decay following inoculation with P, expansum, than dipping into the solution (Conway et al., 1994a). Vacuum infiltration of Ca(N03)2 solutions also increased potato tuber calcium and was efficient in reducing soft rot in tubers inoculated with E, carotovora pv. atroseptica, although an increase in the calcium content of potato tubers could have been achieved by calcium fertilization during the growth period (McGuire and Kelman, 1984). Calcium enters the tissues through lenticels (Betts and Bramlage, 1977), but cracks in the cuticle and epidermis may also provide important points of entry. The extent of cracking may, therefore, play a http://arab2000.forumpro.fr
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Post harvest diseases fruits and vegetables - Xavier University ...

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