Why does violating the integrity of the outer skin of fruits that ripen off the tree or vine terminate ripenin?

Actually, the ripening of fruit may be accelerated by breaking the skin. "There are two types of fruit: climacteric and non-climacteric. Climacteric fruits continue ripening after being picked (which will be accelerated by ethylene gas). Climacteric fruits include: apples, apricots, avocados, bananas, cantaloupes, figs, guava, kiwis, mangoes, nectarines, peaches, pears, plums, and tomatoes. Non-climacteric fruits ripen only while still attached to the plant. Their shelf life is diminished if harvested at peak ripeness. Non-climacteric fruits include: cherries, grapes, limes, oranges, pineapples, and berries (blue-, black-, rasp-, straw-, etc.).

Now, without understanding what hormone was involved, agriculturalists have known about the fruit ripening process for thousands of years. Let’s look at what they knew and see if we can draw any conclusions ourselves:

Ancient Egyptians would gash figs. They noticed this would stimulate ripening. Wounding often stimulates ripening. Even picking an unripe fruit can induce ripening.

Ancient Chinese would burn incense in closed rooms. This would assist pear ripening.

Fruit infected with a bacteria or fungus can cause surrounding fruits to ripen quickly.

In the mid-1800s, people began noticing that some plants were twisted and had abnormally thickened stems. After investigation, it was noticed that only plants near street lights were affected. What do you remember about street lights of the time?

Has anyone told you to put a banana in the bag with your apples or pears to help them ripen?

Does the saying ‘one bad apple ruins the bunch’ actually mean anything?

In 1901, after studying the street light phenomenon, Dimitry Neljubow showed that the active component causing the plant’s malformation was a deceptively simple compound: ethylene!

Ethylene production is induced at several key stages of the plant’s life. Notable for us, ethylene production is promoted during fruit ripening and abscission (dropping) of leaves. However, it is now known that ethylene production can be artificially increased by external factors: wounding of the fruit, environmental stress, and exposure to certain chemicals.

Here’s the problem for the fruit industry. Ripened fruits don’t ship well. That Chaquita Banana commercial with the happy yellow banana in the comfy bed on the ship being transported to the US… not accurate. In fact, bananas are usually picked when green and artificially ripened after shipment. To ripen the bananas, the company gasses the unripe bananas with external gaseous ethylene. Recall from above that exogenous ethylene upregulates the biosynthesis of endogenous ethylene. The bananas ripen, then are sold.

The picking of unripe fruit and artificial ripening later is not uncommon."

You can read more about it here:

http://www.chemistry-blog.com/2011/10/12/fruit-rip...

The skin is just like your skin; if you puncture your skin, infection sets in. Same thing happens with fruits. They start rotting because microbes infect it - bacteria and mold.

Admittedly the fruits rot without the skin cut also; the fruits themselves release enzymes/ethylene to cause that; so that the seeds can get away. But that rot is more of culmination of ripening process - the fruit continues ripening growing ever softer.

About avocado: The avocado fruit does not ripen on the tree, but will fall off or be picked in a difficult, "inexperienced" state, then it'll ripen rapidly on the bottom, but depending on the amount of oil that it has, the taste is also very distinct.