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Melon, Cucumis melo / Cucurbitaceae
Postharvest Atmosphere Management
Pre-cooling is recommended after the harvesting, reaching 4-6ºC in the shortest time possible, with levels of relative moisture between 85-90%. This is made possible by means of forced air, although water pre-cooling is also used. This process is mainly put into effect in netted and cantaloup melons; in this case the temperature of the fruit is 2.2-5ºC.

Concerning conservation capacity, there exist some differences among the different botanical varieties; in the last few years, the seed’s companies have bred some types of melon with a greater capacity of storage (‘Long Shelf Life Melons’).

The netted and cantaloup melons, among which we find Galia and Charentais, are more perishable than the odourless varieties, but they are less sensitive to cold conditions. Their storage may last between 1 and 2 weeks at low temperatures, 0 to 4ºC.

The temperature of storage of the odourless varieties, "Piel de Sapo’, "Tendral´, etc., must be between 7 and 10ºC; under these conditions they are stored, depending on the cultivar, between 2 and 6 weeks.

The optimal levels of relative moisture for storage is between 85 and 90% and it is basic for the post-harvest keeping quality; nevertheless, if the fruit is put under excessively high levels of moisture for long periods of time, melons may suffer from damages on the rind.

Ethylene degrades the chlorophyll and causes the yellowing of the green melon approximately ten days after its application; nevertheless, for the efficiency of this treatment, melons must be harvested in a satisfactory state of maturation. The application of this gas was a common practice in the United States for ´Honey Dew´ varieties, but at present it tends to disappear. "Cantaloup" melons are moderately sensitive to exogenous ethylene, resulting in over-maturation during ¡ distribution and storage.

Research has been carried out on melon storage under controlled atmosphere; the results show that controlled atmosphere on "cantaloup melons" generates certain benefits under conditions of suitable humidity. Hard rind melons (" Negro’ and "Tendral") show the best adaptation to this technique. Maturation is delayed after 14-21 days under CA, respiration is reduced, having an influence in the loss of sugar and the inhibition of the surface deterioration. Levels over 10-20% of CO2 are tolerated, although it may bring along the efervescence of the melon flesh. Low levels of O2 (<1%) or high levels of CO2 (> 20%) result in maturation damage, loss of taste and aroma, etc. The most suitable conditions are 3-5% of O2 and 10-15% of CO2.
Postharvest Problems
Some physiological alterations such as sunburn, chilling injuries, hollow fruit, cracking or water core may affect the fruit, along with fungic alterations caused by various fungi and diseases caused by bacteria.

Physiological alterations:

Sunburn
Mature melons are more vulnerable to this alteration than the green ones. The brown spots turn into black, bearing a chlorotic edge in the area where the fruit has been exposed to sunlight.

Chilling injuries
They are caused by storage for several days at temperatures below 2ºC; in order to prevent this type of injury it is recommended to store the produce at temperatures over 5ºC. The wet holes resulting from the damages exude water to the surface.

Hollow fruit
It is due to hydric imbalances and to the use of phytohormones.

Cracking
It usually has a longitudinal shape. It is caused by hydric imbalances (environmental moisture or irrigation) during the fruit formation.

Water core
It is a degenerative process once the fruit has matured, together with a fast decay. This alteration has been solved with the so-called "long storage melons".

Fungic alterations:

Colletotrichum lagenarium
The disease caused by this alteration is known as antracnosis or fog. The fruit affected shows some rounded cracked spots of brown colour at the beginning and black afterwards, covered with small pink spots.

Cladosporium cucumerinum
It gives rise to some small, concave spots covered by a grey down. It usually appears during transport and storage, sometimes with special virulence.

Fusarium cucurbitae
The rind of those melons with blows and bruises becomes soft and watery, with a rounded injury, not very deep in the flesh. The fungus mycellium is white or pink and it extends with the shape of small brushes.

Botrytis cinerea
Known as " grey mould’, favoured by high temperatures and environmental moisture.

Rhizopus nigricans
It is manifested in wounds and bruises at temperatures over 8ºC. The flesh softens and gives off a slightly bitter scent.

Phytophthora sp.
This fungus causes the appearance of spots in the rind, slightly depressed and with a reddish border. The rind ends up wrinkling and the melon flattens under its own weight.

Bacteria:

Erwinia aroideae
It refers to the well-known " Bacterial soft rot’, characterized by the decay of the rind and subsequent exudation. It usually appears in injured fruit, in rainy and warm harvestings.

Pseudomonas lacrimans
Some wet-like spots appear on the fruit, covered with a bright white exudation.
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