In short, it takes several generations to do this transfer. In each generation, the disease resistant trees are crossed to American trees. Then resistant trees are chosen from among the offspring, and the cross is made again. Each cross to American chestnut trees makes the offspring more like an American chestnut tree and less like a Chinese chestnut tree.
The process continues until blight resistant, American-type trees are produced. It takes at least six years to grow and test each set of trees. So, whether the results of back-crossing are successful or not may not be known for decades.
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