North American Fruit Explorers mailing list at ibiblio

["Lon J. Rombough" <lonrom@hevanet.com>]

Trifoliate orange fruits will give about one teaspoon of juice - the rest of the pulp is full of seeds, and the fruits also contain a bitter resin that quickly gums up anything it contacts.  Cut a fruit and you have to scrape the resin off the knife blade.  
At one time there was a lot of work done in trying to hybridize trifoliate orange with other citrus to get cold hardy citrus.  Some selections weren't bad, but none were very good.  I had a hybrid of pommelo with Poncirus trifoliata that looked like a grapefruit with lots of seeds and wasn't too bad for juice but wouldn't go as a grapefruit substitute.  
The main problem with most of the hybrids is that they produce all nucellar seedlings.  That is, the seedlings come from mother tissue, not from a union of sperm and egg, so it's very hard to get past the initial hybrid to select out the undesirable traits.  
Go to the NAFEX library and look up the late Major Collins' work on hardy citrus.
-Lon Rombough
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On Nov 28, 2008, at 7:23 PM, Stephen Sadler wrote:

<x-tad-bigger>One could also try growing trifoliate orange, an interesting-looking plant that’s extremely cold hardy for a citrus.  The coldest extreme I’ve heard mentioned for it is 20 below; of course, I wouldn’t count on that… There are a few citrus that will survive zero degrees, but I think we’re looking for something even more cold tolerant.  Trifoliate orange is sour and a bit bitter, as I recall; and any citrus is sour when underripe (I expect and welcome corrections whenever wrong, btw).  I hope someone here might have some experience with it as more than just a dwarfing rootstock.</x-tad-bigger>