Commento su Kil'ayim 1:7

Introduction This mishnah discusses the prohibition of grafting.

They may not graft from one tree to another, or from one vegetable to another, or from a tree to a vegetable, or from a vegetable to a tree. This section is in some ways a continuation of mishnayot four and five. The prohibition of grafting is also a prohibition of mixing different kinds of trees or vegetables two different kinds are prohibited. Assumedly, the mishnah relies on the lists already found above trees and vegetables that can be grown together, can also be grafted.

Rabbi Judah permits it from a vegetable to a tree. Rabbi Judah allows one to graft from a vegetable onto a tree (I don’t really know if this works). According to the Tosefta, he also allows from a tree onto a vegetable. The commentators explain that when a vegetable and tree are grafted together, a new species is not formed, even though they the plant grafted onto the mother plant benefits. According to Rabbi Judah, the Torah prohibits the formation of a new species, but does not prohibit grafting when new species will not be formed. The rabbis are stricter and rule that any grafting of different species is prohibited.