I have to ask, how often is tissue culture used? I'm not sure of it's exact usecases like respawning old tree samples but it does seem very related.
Apple trees are pretty easy to propagate if they're alive. Snip off a twig, graft it onto another tree, and away it goes.
Some poor-condition trees can certainly present a challenge in terms of finding ideal graftable wood, but even a poor-quality scion is a lot easier to propagate via grafting than trying to culture in a petri dish.
We haven't been doing that for now. The success rate doing so is somewhat less than directly grafting the whole top of the tree onto rootstock, for a few reasons. Since our primary goal is preservation and a lot of these trees have zero clones and could be wiped out by wildfire on any given year, our first priority is to get clones of every tree.
Do you know any good first resources about this? I'd like to give it a try.