I have had, and just starting some seed again this year of American elm. I second what
@Zach Smith says, the leaves do reduce nicely, once you get some ramification. Also, dutch elm disease is not a problem, as a bonsai tree is too small to attract the bark beetle that carries the disease, and if you do get the disease. the elm being in a bonsai pot, it is easy to drench the tree with the appropriate fungicide.
American chestnut. Castanea dentata - here the chestnut blight is everywhere east of the Rocky Mountains, and persists as many other species of trees and shrubs can serve as alternate hosts for the chestnut blight. There are scattered areas free of chestnut blight west of the Rockies, but I am unclear as to where these areas are. There are some blight free, cultivated American chestnuts in a few northern west coast cities. These trees have no resistance to blight, but persist because the disease is not present there ,,,, yet. So far limited disease resistance has been bred into American chestnut by conventional plant breeding. Strong resistance has been achieved by GMO techniques, using a gene from a grass to achieve strong resistance (not total, but pretty strong). I don't know the availability of the GMO chestnuts. Good resistance is achieved through hybridization with Chinese chestnuts which are immune to the blight. The Chinese-American hybrids have been back bred to be fairly close in character to American chestnut, but they are still hybrids none the less.
The chestnut blight will infect American chestnuts usually by the time they are 10 or 15 years old. In a bonsai pot it might be possible to treat chemically, but I am not aware of any proven fungicide that will work on chestnut blight. Seed of the pure, wild form of the species is expensive when you find it. Seedlings are limited in availability, and there are waiting lists to get the transgenic GMO seedlings. The hybrid trees are of uneven quality and resistance. Some of the hybrids grow low and wide like their Chinese chestnut ancestor, the ones that grow tall like the American chestnut are still uncommon.
The American chinquapin, Castanea pumila - is just as susceptible to blight as the American chestnut. Since it suckers from the roots, and produces seed on fairly young trunks, it has persisted in the wild better than the American chestnut. Seed, when you can find it is expensive.
