Hi guys/gals I am quiet interested how exactly do people develop low-chill variety fruiting plants? I tried searching the internet pretty hard and there seem to be nothing that explains this!

I would love to experiment on developing my own lower-chill varieties of fruiting plants! For example currant/gooseberry/cherry.

Does this involve constantly re-grafting buds/sticks or to a low-chill variety plant or slowly reducing chill hours every year?

What exactly defines/determines the chilling hours of a plant? Is this requirement embedded in the roots or main wood and branches?

I know our climate does change very gradually over very extended period of time so the plants have to adopt some-how and I'm trying to understand exactly how and how to employ this process for my benefit.

I know this should be possible since plant propagators do develop low-chill Peaches(University of Florida)/Cherries(Dave Wilson) with a certain process, and I want to know the process/different ways to do it :D.

Any books or links, advice, or info will be greatly appreciated!

Thanks in advance!