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Celery, Apium graveolens / Umbelliferae
Postharvest Atmosphere Management
Celery
Celery should be first subjected to pre-refrigeration and subsequently, the optimal temperature for preservation is 0ºC with relative humidity between 90-95%.

Celery may be preserved for several weeks and even two or three months at temperatures of 0-1ºC and relative humidity between 90 and 95%. The optimal temperature is 0ºC and optimal relative humidity is 98-100%. To slow down the metabolic processes of the celery, and thus prolong their post-harvest life, they are subjected to a pre-refrigeration process. This may be carried out in a number of ways, with cold air, with cold water (‘hydra-cooling’) or by vacuum, with the last option being the best, due to the rapidity and the fact that it can be applied to celery that is already boxed. The cycle necessary for lowering the temperature from 21ºC to 8ºC may take 13 minutes. Celery must be moistened before bagging to avoid excessive drying with the pre-refrigeration. If good quality is to be maintained, they should not be stored at temperatures above 5ºC for more than two weeks.

Transport may be in refrigerated trucks or not, but good ventilation should always be ensured, depending on the season and the distance to the market.

Regarding the effects of ethylene, at low temperatures celery is not very sensitive to reduced levels of the same in the atmosphere. However, where the concentration of ethylene is 10ppm or more, at temperatures greater 5ºC, a loss of greenness may be produced.

Modifying the levels of the components in the atmosphere may lengthen the preservation time of the green colour and control the appearance of putrefaction. The controlled atmosphere for the combined storage of celery and lettuce or its long-distance transport has a commercial application. Elevated levels of CO2 retard the yellowing and rotting of the celery leaves, but is not recommended in mixed loads with lettuce, as it does not tolerate atmospheres enriched with CO2. It is also known that there are senescence delays with 2-4% of O2 and 3-5% CO2.
Postharvest Problems
The problems of post-harvest of celery that can be produced are fading, yellowing, different rotting caused by fungus and some physiological alterations.

During the post-harvest period, there can be changes produced in the celery due to physiological alterations and others produced by illnesses.

The main post-harvest problems are the following:

Wilting
Produced when the celery loses water. The leaves dry out, shrinking, changing texture and losing weight. It is recommended to subject celery to relatively high conditions of moisture to retard this withering process.

Yellowing
Caused by the degradation of chlorophyll. A process associated with senescence.

The main illnesses affecting it are:

Grey Mould
Caused by the Botrytis cinerea fungus that grows above all on the petioles. The appearance of the affected tissue is first watery and lightly consistent, and after turns a greying colour and becomes soft. If the relative humidity is also excessively high, it becomes covered with grey mycelia that can spread to adjacent pieces and form nests.

Atmospheres low in oxygen (1.5%) with 7.5% CO inhibit the growth of the mycelia and the sporulation of the fungus. These effects are also obtained, to a lesser degree, if the CO is substituted by 4% CO²

Water Rot
Caused by different fungus belonging to the Sclerotinia genre. The attack of these fungi happens during growth, especially in rainy periods. The affected plants are not normally picked but the infection may not be detected in some in the initial stages and thus, may advance during post-harvest causing watery, soft stains that are a light-grey colour with a pink border. The neck and base of the leaves become covered with pinkish-white mycelia over which sclerotia develops, which is black.

Soft Rot
Caused by the Erwinia carotovora bacteria. The tissue first has a watery appearance and then later changes to a greyish-brown colour with an unpleasant odour. If relative environmental humidity decreases, the bacteria stops advancing, and the affected zone appears dry and sunken. In this case, the illness is called ‘crat rot’.

Cercospora Apii
Symptoms begin with circular, yellow stains on the foliage that later turn to greyish-brown tones. These stains spread quickly, and can cover entire leaves and petioles. Later, the stains turn grey again, until resulting in foliage necrosis.

Mycocentrospora Acerina
Also known as Liquorice Rot. The fungus produces black damage almost always near the base of the petiole of the outermost leaves. It may attack during growth, producing stains similar to those of Cercospora as well as during post-harvest.

Physiological Alterations:

Holes in the petioles
Due to the susceptibility of some varieties to freezing, drying or over-maturing in the fields, the alteration is produced that starts on the petioles of the outermost leaves. If the affected celery is stored for a long time, the sugars move towards the inner petioles and cause cell death, and holes.

Black Petioles
Also known as ‘black-stem’. The affected celery frequently presents longitudinal black lines and if cut, the blackened veins can be observed. Sometimes, the black stains spread over the entire surface of the petiole. Above all, it affects the inner leaves. Another alteration whose symptoms are similar is that known as ‘Pencil stripe’, although this appears in the fields and the black colour advances from the nodes.

Atmospheres with 3% de O² and 2% CO² practically prevents the appearance of this alteration of celery.

Black Heart
A greyish-brown or dark black colour is observed on the inner leaves. It is produced due to poor movement of the calcium and may be due to a high saline content in the soil, excessive nitrogen and potassium, lack of sun, soil with poor calcium content or lack of hydric equilibrium.
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