Allelopathy is understood to mean the mutual influence exerted by goods of vegetable origin through the gases they give off, which have an effect on metabolism. In this way, in ripening fruit in particular traces of ethylene (C2H4) are formed and pleasant-smelling aromatic substances are formed and released. Since respiration is at its most intensive in the climacteric, a particularly large amount of ethylene is produced in addition to carbon dioxide and may cause fruit nearby to ripen more quickly. A concentration of 0.02% of ethylene in air accelerates the ripening process by 4 - 10 times. Ethylene-producing goods of vegetable origin are divided into five groups (see Table 6 and Fig. 82).
Ethylene production rate
Chinese artichoke, Japanese radish, prickly pear, Florence fennel, cassava, pak-choi cabbage, cranberry, black salsify
Very low:
0.01 - 0.1
Pineapple, artichoke, cauliflower, broccoli, watercress, mushroom, chicory, Chinese cabbage, date, endive, pea, Jerusalem artichoke, grapefruit, curly kale, ginger, carrot, potato, cherry, garlic, celeriac, kohlrabi, lime, sweetcorn, mandarin, horseradish, orange, parsnip, parsley root, chanterelle, leek, radish, rhubarb, Brussels sprout, beetroot, red cabbage, turnip, green cabbage, asparagus, spinach, rutabaga, celery, sweet potato, tangerine, taro, grape, white cabbage, lemon, onion
0.1 - 1.0
Winter cherry, aubergine, egg-plant, berries, bitter squirting cucumber, Seville orange, bean, clementine, persimmon, iceberg lettuce, baby sweetcorn, pomegranate, guava, cucumber, starfruit, kiwifruit, coconut, cabbage lettuce, kumquat, pumpkin, limequat, olive, sweet pepper, chili pepper, quince, garden radish, satsuma, watermelon, courgette, zucchini
1.0 - 10.0
Banana, fig, feijoa, honeydew melon, Jack fruit, lychee, mango, mangosteen, plum, tomato
10.0 - 100.0
Apricot, avocado, tamarillo, pear, papaya, peach/nectarine
Very high:
> 100.0
Apple, cherimoya, passion fruit

Table 6: Ethylene production of various types of fruit and vegetables;
taken from Alders (with additions) [2]
Fruits may be divided into two categories on the basis of their respiration profile: "climacteric fruits" and "non-climacteric fruits", (see Table 7).
Climacteric fruits Non-climacteric
Apples Pineapple
Apricots Blueberries
Avocados Strawberries
Bananas Cucumbers
Pears Limes
Figs Oranges
Kiwifruit Satsumas/mandarins
Mangoes Grapes
Papaya Lemons
Passion fruit  

Table 7: Classification of goods of vegetable origin by respiration behavior
during ripening; taken from Alders [2]
Climacteric fruits display the typical respiration profile, as illustrated in Fig. 79 using bananas as an example, which is associated with high levels of carbon dioxide and ethylene production during ripening. Non-climacteric fruits, e.g. potatoes, root vegetables, strawberries, do not display the increase in respiration rate known as the "climacteric rise"; instead, the respiration rate falls during ripening, with only small amounts of ethylene consequently being produced.

Figure 79: Ripening of bananas
1 - preclimacteric (green)
2 - climacteric (turners)
3 - postclimacteric (yellow)
"c.r." - "climacteric rise"

When transporting fruit of a single type by container, it must be ensured that the transportable unripe fruit at the preclimacteric stage is not stowed together with fruit in an advanced state of ripeness, because the ethylene released by the ripening fruit causes the unripe fruit to ripen prematurely. If one item of fruit begins to excrete ethylene, a whole container cargo may begin the increase in respiration associated with the climacteric (see turners in cargoes of bananas).
If an on-board porthole system is used, all the fruit in all the containers with which it is connected may then suffer premature ripening, which may amount to as many as 100 metric tons of bananas, for example.
In addition to the increase in respiration, ethylene initiates other normal ripening processes, such as chlorophyll degradation, starch hydrolysis and sugar build-up.
When fruit and vegetables of various types are being transported by container, care must be taken to ensure that the types of fruit and vegetables belong to different categories of ethylene producer, as shown in Table 6 and Fig. 82. Thus, for example, apples, which produce large quantities of ethylene, cause potatoes to germinate prematurely. Cucumbers turn yellow on exposure to ethylene from apples or tomatoes. Table 8 shows the ethylene sensitivity of various types of fruit and vegetables.
Zero Seville orange, Chinese artichoke, clementine, fennel, kumquat, pak-choi cabbage, chanterelle, cranberry, garden radish, satsuma
Low Pineapple, winter cherry, artichoke, aubergine, egg-plant, berries, bitter squirting cucumber, date, Jerusalem artichoke, fig, feijoa, baby sweetcorn, pomegranate, ginger, prickly pear, starfruit, carrot, cherry, garlic, celeriac, coconut, pumpkin, sweetcorn, cassava, horseradish, sweet pepper, parsnip, chili pepper, parsley root, radish, rhubarb, beetroot, turnip, black salsify, rutabaga, sweet potato, taro, grape, watermelon, onion (dry)
Moderate Tamarillo, bean, mushroom, endive, pea, Jack fruit, grapefruit, guava, potato, cabbage lettuce, lime, lychee, mandarin, olive, orange, leek, asparagus, celery, tangerine, lemon, courgette, zucchini, onion (green)
High Apple, apricot, avocado, banana, pear, cauliflower, broccoli, watercress, cherimoya, chicory, Chinese cabbage, persimmon, iceberg lettuce, curly kale, cucumber, honeydew melon, kiwifruit, mango, mangosteen, papaya, passion fruit, peach, plum, quince, Brussels sprout, red cabbage, spinach, tomato, white cabbage, savoy cabbage

Table 8: Ethylene sensitivity of various types of fruit and vegetables;
taken from Alders (with additions) [2]
In practice, ethylene formation is prevented to a considerable extent by a specific dormancy temperature together with reduced respiratory activity (see Section On the other hand, this effect may be used to advantage in ripening warehouses to bring about ripening at the desired time by exposure to ethylene.
Measurement of ethylene concentration may be performed using an ethylene monitor (see TIS).
Figure 82: Ethylene production of fruit and vegetables

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