Commentary for Avodah Zarah 40:19

Rabbi Meir holds that one should not even rent houses to non-Jews in the land of Israel, lest he come to sell them as well. This is true of houses and even truer with regard to fields, for with fields there is the added problem of tithes. Once a Jew sells his field to a non-Jew the field’s produce is not liable for tithing. In this way, the sale reduces the holiness of the field. In Syria, which is adjacent to Israel and was conquered by David but is not considered fully a part of Israel, we can be slightly more lenient. Houses may be rented to non-Jews, but fields still may not, because the produce grown in Syria is still subject to tithes. Outside of the land, a Jew may sell houses, but he still may not sell fields, lest by habit he come to sell fields in the land of Israel as well.