פירוש על קידושין 77:15

But, Ulla continues, according to Shmuel’s view, there should be no difference in the rules governing buying orlah and kilayim from a Gentile outside the Land. Both have the same status—prohibited by the rabbis.

Shmuel did indeed emend one of the mishnayot such that both read the same. Thus he accepted Ulla’s criticism.

Mar son of Rabbana, a late amora, was lenient in both cases—as long as the Jew does not gather the orlah or kilayim, the produce is not prohibited.

In the first two cases rabbis will eat orlah outside of Israel, but they will not pick it themselves. It seems that in this way, they can pretend that they’re not sure that this is orlah, and doubtful orlah is not prohibited outside of Israel.
The rabbis of Pumbedita go a step further and say that the prohibition of orlah does not apply at all outside the land of Israel.

R. Yohanan vehemently disagrees with the scholars of Pumbedita. He instructs R. Yehudah, the founder of the school of Pumbedita, to hide the law that doubtful orlah is permitted outside of Israel, he tells him to destroy certain orlah and that doubtful orlah must be hidden. He concludes with a strong exhortation, condemning those who say that there is no prohibition of orlah outside of Israel. The line from the book of Michah about casting a “line by lot” refers to receiving an inheritance. Those who say that there is no law of orlah outside of Israel will not take part in any future inheritance of the land.

The opinion held by the scholars of Pumbedita has a strong pedigree too.

In the mishnah R. Elazar said that “also new produce” is observed outside the Land. This seems to mean that he agrees that kilayim and orlah are also observed outside the Land. That’s why he said “also.” Assuming that R. Elazar is the same sage as “R. Elazar the Great,” then how can he say above that there is no prohibition of orlah outside the Land?
To resolve the problem the Talmud now erases the word “also.” To R. Elazar only the prohibition of “new produce” is observed outside the land—not kilayim and orlah.

R. Yohanan rules that the prohibition of orlah outside the Land is a halakhah to Moses at Sinai. This is a status almost akin to the status of prohibited by the Torah. But R. Zera raises a difficulty on this position. Doubtful orlah is permitted outside the Land. This would seem to mean the prohibition of certain orlah is lower than that of a “halakhah of Moses from Sinai.” R. Assi responds by including the distinction between doubtful and certain orlah into the halakhah of Moses from Sinai. In other words, when the halakhah was given to Moses, it reflected the same halakhah found in the baraita.

In this second statement by R. Assi in the name of R. Yohanan, the sage claims that kilayim is prohibited by the Torah outside of Israel. He expresses this by referring to the punishment for the transgression—a normal way for the rabbis to express the level of a prohibition. If the prohibition is considered to be from the Torah, then it is theoretically punished by lashes.
This again contradicts the baraita we saw earlier, which stated that kilayim outside of Israel is only a rabbinic prohibition.
The answer is that there are several different types of kilayim. One is the prohibition of planting seeds in a vineyard (Deuteronomy 22:9). This prohibition is only “derabanan”

This story takes place outside of Israel. When the two rabbis see someone planting diverse seeds, one rabbi wants to put the planter under a ban, a very serious punishment. The other rabbi refuses, telling his fellow that this halakhah is not clear to him.

This time they see another Jew sowing seeds in a vineyard, and again one rabbi wants to ban the man. But again, the other rabbi refuses, this time explaining that his fellow does not know that one is not liable for sowing seeds in a vineyard unless he throws down the different seeds in the same act. We should maybe detect here a note of one rabbi rebuking another for trying to punish someone without being 100 percent sure that he is deserving of the punishment.

The rules of mixed seeds in a vineyard are stringent inside the Land—one may not derive any benefit from them. Therefore, outside the Land the rule is also stringent. But the rules regarding planting mixed seeds are lenient inside the Land—one may not eat the plants that grow, but one may derive benefit from them. Therefore, this rule is not observed outside the Land.

R. Joseph now retracts his statement that outside of the Land one may plant mixed seeds. The basis for this retraction is the actions of Rav, a Babylonian amora, who seems to plant the garden of the rabbinic academy in rows in order to prevent the mixture of the seeds.

Abaye rejects R. Joseph’s reading of why Rav planted the garden in rows. If he had planted it in the way that gardens were to be planted in order to avoid the mixing of the seeds (four sides of a square, each with a different species and one row of another species in the middle), then we could be sure that he was doing so in order to avoid the problem of kilayim. But since this is not what Rav did, we can offer other assessments of his motivation. He might have done so either because this makes the garden look nicer or to save the attendant, the one harvesting the vegetables, the trouble of having to search for what he was looking for.