I have seedlings that fruited in 3 years and another going on 6 years with no fruits. Planted within 15' of each other. The one that produced in 3 years was not attacked by the japanese rose beetle. I feel as though the beetle sets it back tremendously. I would suspect there is something in the leaves that either makes the tree attractive or not attractive. If breeding, success would be increased by finding a type the beetle doesn't care for. If you find your tree continuously getting attacked by beetles, start over, as it may be faster.