some little bit of info about chestnut and elm:
http://www.endangeredspecieshandbook.org/projects_saving.php
ah ha! Here it is.
http://www.libertyelm.com/about.htm
The Liberty elm is not a hybrid. ERI’s American Liberty elm is actually a group of six genetically different cultivars. All six look like classic, old fashioned American elms. “You have to look closely and know what you’re looking for to tell the difference among the six,” says Hansel. “To be sure which one you have, you really need DNA analysis.”
Genetic differences provide diversity. Having six cultivars in the series is insurance against all the elms being wiped out by any disease or problem, even one that might show up in the future. ERI mixes all six cultivars in its shipments.
The difference with elms is that while Dutch Elm Disease is also destructive, it’s not quite as rampant as Chestnut Blight, to where it’s not all that unusual to see American Elms of large size here and there, but large American Chestnuts are VERY rare, some feel there are less than 100 large, healthy American Chestnuts left in North America.
I see 100 American Elms on my way to work each day. They WILL get DED and die eventually, but most of them live to be old enough to reproduce and therefore the species is a lot more common.
That said the resistant-elms could also prove to bring the species back to it’s fullest extent.