Why my apricot/peach graft failed (part 2) - How to test if a root is alive or dead

After it became certain the graft had failed, I took the tree apart to determine what had gone wrong. As you can see, there is no green under the bark. It appears that the tree is dead all the way down to the roots, so the graft never had a chance. I still don't know what killed the tree, but I'm guessing the roots were too soggy. I mixed more woodchips into the soil after removing the dead peach tree.