) for 3 or 7 days of storage at 18ºC deteriorated rapidly. Exposure to reduced the rind thickness and firmness of melons. Almost all of the melons exposed to 30 or 60 ul/liter ethylene for 7 days were unacceptable for consumption. Sugar content does not change after harvest, but flavor may be improved due to loss in acidity of slightly immature melons. Fruit can get over-ripe fairly quickly if not cooled. However, watermelon color will continue to improve for up to 7 days after harvesting if kept at temperatures of 18º- 22ºC, but it will actually fade (get lighter) if kept at temperatures of below 12ºC for long periods of time. It is important to note that once harvested the sugar content or sweetness will not improve. Chilling injury will occur after several days below 5ºC. The resulting pits in the rind will be invaded by decay-causing organisms. Moisture content and pH of the injured watermelon were higher than those of normal watermelon. However, color tone (Lab), hardness, soluble solid, and total amino acid and sugar contents of the injured fruit were lower than those of normal fruit.
Watermelons exposed to various concentrations of ethylene () for 3 or 7 days of storage at 18ºC deteriorated rapidly. Exposure to reduced the rind thickness and firmness of melons. Almost all of the melons exposed to 30 or 60 ul/liter ethylene for 7 days were unacceptable for consumption.
Less than 50% of the melons exposed to any concentration of ethylene were acceptable for consumption.
Watermelons, particularly early in the season, are sometimes shipped in mixed loads with other produce or they may be stored in central warehouses near products that may emit .
Watermelons are usually harvested at their peak maturity and flavor, generally will not improve with storage. An increase in production is associated with the respiratory peak and with the end of senescence after harvest.
Watermelons are detrimentally affected by ethylene and should not be held with cantaloupes, honeydews or other mixed melons. The whole fruit may become spongy and the internal pulp may become mealy and breakdown if exposed to low concentrations (>0.5 ppm) of ethylene.
Principal Postharvest Diseases: Postharvest diseases are important sources of postharvest loss in watermelon production. This loss depends on cultural practices adopted during production and also the local climatic conditions at harvest. Disease pressure is greater in areas with high rainfall and humidity during production and harvest. A number of pathogens may cause postharvest decay of watermelon. The primary defense against the occurrence of decay is the exclusion of diseased fruit from the marketing chain through careful selection at harvest and appropriate fruit grading before shipment. Holding fruits at 10ºC will slow down the rate of disease development, compared to ambient temperature storage. There are no postharvest fungicide treatments for watermelon. Common fungal diseases that cause rind decay after harvest include black rot (Didymella sp.), anthracnose (Colletotrichum sp.), Phytophthora (Phytophthora sp.) fruit rot, Fusarium, and stem-end rot (Lasiodiplodia theobromae). The most common postharvest bacterial disease is soft rot.
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Anthracnose decay of watermelon fruit. |
Greasy spot and associated whitish mold growth of Phytophthora infected fruit. |
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| Fusarium rot on 'Sugar Baby' watermelon. | Symptoms of stem-end rot. |
For more information on diseases of watermelon go to: http://watermelons.ifas.ufl.edu/diseases/diseases.htm