Chokkon
It refers to a root that comes out for the first time directly from under the place where its seed is planted. It is also called a burdock root. The force of the root to extend underground enables a tree to grow its height and a trunk to become thick. If visible roots of a tree should be handled well early, the spreading of deep roots in all directions takes place by removing the chokkon root while it is young.
translated by Kyodo News