The grafted etrog
Grafting, a widespread agricultural procedure, involves attaching a branch of a certain tree to a tree of a different species. It is particularly common to graft branches taken from cultivated trees onto wild trees, which are considered agriculturally stronger and more immune to botanical disease. Over the course of many generations, people would commonly graft branches of etrog trees onto lemon trees. We refer to an etrog grown in this manner as "etrog ha-murkav," or a "grafted etrog."
The Gemara never addresses the suitability of such an etrog for the mitzva of the four species on Sukkot. Nor do we find any Rishonim who address the issue. The discussions concerning this issue begin to appear only in the last several centuries. The Acharonim dealt with this question at length and gave different reasons to disqualify an etrog ha-murkav from use on Sukkot. We may classify all the different reasons under two general categories:
A) We disqualify the etrog because the identity of its species.
B) The etrog is invalid because of the prohibition that had been violated through the grafting procedure.
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