Grafting has been developed for horticultural crops as an agricultural method in Japan. Grafting is a method to combine two kinds of plants. For example, it is possible to generate a crop that is robust to disease and tasty by combining a crop that is sensitive to disease but tasty and a crop that is robust to disease but tasteless. Grafting has been often used for agriculture. However, it is still unclear why two different plants are able to combined and bear fruits.