I also posted a question to Alias concerning his early grapefruit.

As said earlier and gone, I am one of the discoverer of the grapefruit.
This is a random glitch that has a more than 30 years planting.
The plant is largely -12 ° c and spent 2012 with just a few fell to -18 ° C leaves.
In terms of fruit, it is more resistant to cold than the duncan.
While duncan to -5 ° c, then this task falls to the ground, the enzo does nothing.
The small plane grafted my friend Bernard (not Voss to meet Mikkel: Message deleted) had major damage at -18 ° c but it returned with a vengeance.
The ripeness of the fruit is from December but I prefer sweeter around March.
I have another type of grapefruit which is much earlier (mature late November) and softer, grapefruit Welker.
Grapefruit Enzo is turning yellow pink orange at full maturity while Welker is yellow.

We have just deleted me a message?

Alias,
What is this Welker grapefruit? I found no information on it on the web, even in the listing of your collection on Agrumes Passion. Could it be the same as Golden grapefruit of US?

The grapefruit welker is a cousin of Enzo in the sense that it is a seed that was planted.
Enzo grows in a small village at the foot of the Cévennes (small mountain) and Welker pushes Aubagne in France in a very cold area famous.
The only grafted plants are at my friend bernard and home.
It was found that in the south east of France many Grapefruit lived for over 30 years without any real damage.
Its products are all from seed.
There are therefore as many as seed cultivar.

Thank you Alias,
What is the resistance limit of this Welker grapefruit? -10C?

It is cold hardy as the enzo.
To date, there is no significant difference in resistance to cold.

@alias

the facts you have given are very promising.
This could be a good crossing partner. Does Enzo or Welker have zygotic or at least any seeds?
is there a source for Welker? I know only a nursery for Enzo. Can you help?

I would also like Grapefruit Welker and Enzo if there is a source. I would be able to grow them in my garden unprotected, and also to make hybrids with them

you lucky one