The American Chestnut is not extinct as many believe. We have a half dozen or so on the farm. It has been some years ago, but there was a biologist from state university who was at the farm. She said how many had been planted. I can not remember now, but I know it was in the million. She said in the prime, there were so many billion of the American Chestnut Trees. I do enjoy the roasted nuts at Christmas time.
I agree with the hybridized trees. Seems like you mess with nature and it never works out. The biologist also said that no trees were immune, but the Japanese and Chinese chestnut trees grow over the infection where the American trees will not. Again, I am going by memory. It’s been years and I have slept, several times, since then. Like @Errant alluded to, she called it a "century project" meaning that the people working so hard to bring the American Chestnut back to its former glory will never see the fruits of their labor.