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Grafted and Hybrid Etrogim

Grafted and Hybrid Etrogim

What is a grafted etrog? About the problem specifically in grafted etrogim, the rationale for the prohibition against kila'im, the definition of a pure etrog, and the significance of taking a kosher set of the arba minim

Prof. Zohar Amar, Emunat Itecha, 72 (5768), pp. 36–43

A.   What is grafting?

The issue of the grafted etrog has been the subject of extensive discussions in halachic literature. Indeed, this chapter has been expanded into an entire book.[i] In the footnotes, we will also mention several related historical, linguistic, and agronomic issues as well. The prohibition of grafting two different species of plants or cross breeding two species of animals is a negative biblical injunction, called kila'im (lit. mixture) (Vayikra 19:19; Devarim 22:9–11); indeed, the entire tractate Kila'im is dedicated to this topic. The prohibition of crossbreeding different species of animals is also known in Talmudic literature as harkava.[ii]

Harkava, or grafting, is the term generally used in the laws of kila'im as it relates to the technique of connecting certain plants (rochev, scion) onto other plants from a related family (kana, rootstock)[iii] and the formation of a common tissue that fuses the two together. The scion brings with it the characteristics of the desired fruit, while the rootstock provides the resultant tree with hardiness (to withstand maladies, pests, and the ability to adapt to soil conditions that the scion is incompatible with), the ability to receive nourishment and water from the soil. The rootstock, among other things, also influences the tree's vegetative vigor, its size, and yield.

Until recently, modern research maintained that there are no genetic influences between the scion and rootstock, and that each retained its independent qualities, despite the fact that they receive nourishment from one another. In the past decade, however, it was proved that the scion-rootstock relationship includes gene silencing, regulated by RNA particles. These findings indicate that there are mutual genetic influences, but not that grafting creates a new species.[iv] With citrus trees, for instance, the rootstock influences the fruit's characteristics; nevertheless, influences have not been found to produce a hybrid—such as with sexual propagation produced by the union of a male gamete from one pollen cell with an egg of another plant to create an embryo that carries the genetic characteristics of both parents.[v] That is, if I plant seeds from a fruit that grew on a grafted tree, there will be no genetic influence on the fruit of the resulting tree and no one will know that the fruit was from a grafted tree.

The term harkava is also mentioned in the context of dates: the residents of Jericho would "markivin palm trees," an action that is permitted in and of itself, but that the Sages opposed when performed on erev Pesach.[vi] Today we know that it is impossible to graft palm trees, since they are monocot plants. These plants (as opposed to dicot plants) lack cambium tissues—present in other trees—which has a regeneration capacity, facilitating new tissue formation upon grafting. Therefore, it is clear that this act mentioned in the Mishnah was not grafting but pollination: initiated sexual propagation through the artificial propagation of the male date blossoms in the female date blossoms.[vii] While it seems that in ancient times people were not aware why the vegetative sexual propagation process worked as it did, through accumulated experience they were familiar with this act.[viii] In light of the similarity between the process of pollinating the palm trees and grafting a scion and rootstock, both are known under the name harkava.[ix]

In summary, the term harkava in Talmudic literature includes the technique of scion-rootstock grafting, and rarely, pollination, which is similar to producing hybrid animals through sexual cross-breeding.

B. The problem of grafted etrogim

During the times of Chazal there were different varieties of etrogim available (as there are today), as indicated by textual sources and coin artifacts; large and small, with and without a pitom, bumpy and smooth, some with "narrow waists" (a gartel).[x] These different etrog varieties were apparently cultivated by an act called sipuk: grafting the blanch of one etrog tree onto another from the same species.[xi] Even so, the problem of grafted etrogim is not mentioned by Chazal and there is no indication that such a problem existed in the times of the Mishna or Talmud. Moreover, various types of citrus fruit, such as the hushhash (bitter orange) and the lemon are mentioned extensively only in later literature in the context of a concern of grafted etrogim. This practice entered the agricultural culture in the Middle East only in the Middle Ages.[xii] Indeed, it is only from this period do we hear about the possibility of grafting an etrog with various trees and the possible connection to other types of citruses. In many cases, this is impossible, fantastical grafting, which can be included under the genre of agricultural folklore—such as can be found in the composition by Ibn Wahshiyyah the Nabataean of the 10th century. His work mentions, for instance, grafts of etrog trees with olive or pear trees[xiii] or echoes of the belief that the orange was developed from the etrog.[xiv] Theoretical Arabic agricultural literature mentions grafts of etrog and apple trees;[xv] it seems that this is the Rambam's source of the examples he gives for the prohibition against grafting trees of different species (citing these two species).[xvi] Al-Baghdadi, a physician who was Rambam's contemporary, described various strains of etrogim which seemed to have developed from the hybridization with other citruses.[xvii] In any case, note that the first testimonies of the concern regarding grafted etrogim appear in halachic literature in the 16th century—in the Land of Yisrael, in Italy and Poland.[xviii]

The point of departure of this article is that the etrog, the lemon, and orange are all considered separate species, which is why it is prohibited to graft them with one another or with their offspring.[xix] Note that the prohibition vis-à-vis etrogim (in contrast to other fruit trees) it not only the act of grafting; although the product is permitted to eat post-facto (just like other fruits of trees grafted in a prohibited manner),[xx] it is forbidden to use a grafted etrog for the mitzvah of taking arba minim.

There are extensive references in halachic literature to the differences between pure and grafted etrogim. The most significant markers of the etrog are its bumpy, thick skin, sunken oketz (peduncle), lack of juice, and vertical seeds (the last sign is not accepted by all opinions). In contrast, grafted etrogim have a thin and smooth peel, a raised peduncle, horizontal seeds, and juicy pulp. All of these changes are not genetic, rather the result of grafting. It is for this reason that the shoots taken from a grafted etrog tree (scion) or seeds of its fruit will produce fruit with only the characteristics of a pure etrog; all the rest of the rootstock's characteristics will disappear.[xxi]

C. The relationship between grafting and pollination

Why does the concern regarding grafted etrogim today only have to do with etrogim grafted through the scion-rootstock method—and not with a genuine hybridization through pollination between the various types of citruses, which can take place naturally without human involvement or supervision? Moreover, in the pollination process, wouldn’t the genetic influence on the fruit be more significant than with a grafted etrog? Could it possibly be that in the description of grafted etrogim and their characteristics as they appear in some of halachic literature, there is an interchange of terms: that is, they describe the product of hybridization through pollination, and not a graft, since both acts fall under the halachic umbrella of the term harkava?

The poskim certainly discussed the relationship between grafting and hybridization of etrogim, and answer several aspects of the questions we raised.[xxii] Our conclusion is that it seems that the grafted etrog is invalidated since the prohibition of kila'im was transgressed—the changes that actually occur in the fruit are only testimony of the forbidden action performed. For this reason, it doesn't matter what level of actual change takes place in the etrog: even if it is not apparent from the etrog's characteristics (and even if no physical change is apparent)—the very fact that a forbidden graft was performed[xxiii] casts aspersions on the purity of the species of the peri eitz hadar, which is permitted based on the tradition for the mitzvah. This strengthens the opinion that the rationale of the prohibition of kila'im is meddling with G-d's creation. However, if the hybridization takes place in a natural manner, the product is permitted—since in this way it is G-d's way of showing that He is interested in the creation of this variety.[xxiv]

It turns out that this explanation not only reflects the philosophical idea behind the mitzvah, but is congruent with the botanical and genetic reality as well. Natural hybridization (through wind or insects) between an etrog and another citrus are apparently not common, or do not produce offspring that exist long-term. In the end, the vast majority of etrogim available are the product of same-species pollination {fertilization}. This conclusion is also indicated by genetic studies conducted on various etrog strains (Yemenite, Moroccan, Chazon Ish, Calabaria (Diamante), etc.), which prove that there is vast genetic similarity among them. On the other hand, the study indicates that there are significant differences between the etrog and other citruses, lemons included, thus waiving the concern that the various etrog strains are hybrids with lemons or other citrus. The findings of the study point to a common origin for all types of etrogim; it seems that all of them—including the Moroccan and Yemenite etrogim—are from the Mediterranean basin. And in the words of E. Goldschmidt: "In light of these findings it is possible to say in certain degree of certainty that the etrogim in our hands are 'all beloved, all clear.' All of them are genuine etrogim and are not the results of a hybrid of an etrog and a lemon or other citrus fruit." In contrast, the genetic study could not discern between an etrog that is the product of a graft, and one that was never grafted. Moreover, the findings could not prove that any one of the etrog strains was definitely ungrafted.[xxv]

In conclusion, in light of the scientific research, the concern regarding grafted etrogim as it appears in halachic literature refers to scion-rootstock grafts and not cross-pollination. A graft between similar species of trees is permitted, since naturally it is possible to propagate them. For this reason, it is permitted to graft different pure varieties of etrogim with one another. Pollination is also called harkava, but since it is a natural process, it is permitted, similar to the harkavat dekalim, which is an act that enhances a process that can occur naturally otherwise.[xxvi]

D. Defining a pure etrog variety

This topic is another example of the difference between the halachic and scientific definition of "species." The halachic definition is broad and can change in light of various indices, and is not necessarily measure in light of the degree of genetic similarity between two organisms. A grafted etrog is not considered a species of etrog (that can be used as one of the arba minim), even though, theoretically speaking, its genetic similarity is larger to a genuine etrog than the product of a natural hybridization that can develop between an etrog and other types of citruses. The link between the myrtle with three-leaved nodes we use for the mitzvah of taking a hadas and the wild myrtle is a similar issue. We see that they are halachically considered two separate species, even though genetically they are considered the same species, from which there are two presentations.[xxvii]

E. The idea behind taking a kosher set of arba minim

The issue of the identity of the genuine species of the arba minim and the rationale behind taking them is mentioned in Talmudic literature, and the question about the kashrut of the similar species are discussed throughout the Acharonim regarding the arava (Salix includes many common hybridized species);[xxviii] and the lulav (such as the Canary Palm).[xxix] It turns out that specifically taking all of the arba minim symbolizes not only the aspiration for unity among all parts of the Jewish People and their spiritual elevation,[xxx] but also a demand for the clarification of its pure genetic identification. This is why different "species" that are not of Jewish descent are not allowed to marry within the Jewish community. This was the case in the days of Ezra and Nechemiah, after building sukkot, all of the gentiles were distanced from the Jewish seed:

They found written in the Teaching that the L-rd had commanded Moshe that the Israelites must dwell in booths during the festival of the seventh month, and that they must announce and proclaim throughout all their towns and Jerusalem as follows, “Go out to the mountains and bring leafy branches of olive trees, pine trees, myrtles, palms and [other] leafy trees to make booths, as it is written.” So the people went out and brought them, and made themselves booths on their roofs, in their courtyards, in the courtyards of the House of G-d, in the square of the Water Gate and in the square of the Ephraim Gate. The whole community that returned from the captivity made booths and dwelt in the booths—the Israelites had not done so from the days of Joshua son of Nun to that day—and there was very great rejoicing. … On the twenty-fourth day of this month, the Israelites assembled, fasting, in sackcloth, and with earth upon them. Those of the stock of Israel separated themselves from all foreigners, and stood and confessed their sins and the iniquities of their fathers. (Nechemiah 8:14 – 9:2)

*I would like to thank Rabbi Yoel Friedemann for his important comments.


[i] Indeed, this chapter has been expanded into an entire book: Zohar Amar, Arba'at haminim – iyunim hilchatiyim bemabat histori, botani, ve-eretz yisraeli (The four species: halachic studies through the lens of history, botany and the land of Israel), Neve Tzuf, 5770. See especially pp.41–54 (Heb.). 

[ii] See, for instance, Pesachim 54a: "Adam brought two animals (a female horse and a male donkey), and mated them with each other, and (the resultant offspring that) emerged from them was a mule."

[iii] Mishnah Kila'im 1:8; Yerushalmi Kila'im 1:4.

[iv] This is Prof. Goldschmidt's comment to me on this article.

[v] This subject is discussed at length by Prof. Yehuda Feliks, "Kilei zera'im and grafting," Tel Aviv 5727, pp. 7–13 (Heb.); Prof. Eliezer Goldschmidt, "The problem of the grafted etrog and the nature of etrogim prevalent today," Techumin, 2 (5741), pp. 135–145 (Heb.).

[vi] Mishnah, Pesachim 4:8.

[vii] See HaAruch (the earliest dictionary on Talmudic literature: Natan ben Yechiel, Rome, 11th Century), entry Nasan.

[viii] An additional example of artificial cross-pollination is the method of hanging male flowering branches of the caprifig or caprifigs in the trees of domesticated female fig (this facilitates pollen transfer by fig wasps – MB), which, in turn, develop its fruit. This process is called caprification. See Prof. Yehuda Feliks, "Types of fruit trees," Jerusalem, 5744, pp. 50–51, 91–93 (Heb.).

[ix] See Rivka Brand, "Grafting palm trees," Techumin, 13 (5752 – 5753), pp. 106–115; Mordechai Kislev, "Why did the Sages permit the people of Jericho to pollinate date palms on Sabbath eve," Ketedra, 72 (5754), pp. 13–22 (Heb.); Solomon Gandz, "Artificial fertilization of date-palms in Palestine and Arabia," Isis, 23 (1935), pp. 245–250.

[x] Yerushalmi, Sukkah 3:7; Bavli, Sukkah 36b; Ya'akov Meshorer, Treasure of Jewish coins, Jerusalem, 5758, pp. 128–129 (Heb.).

[xi] Yerushalmi, Orlah 1:3. Regarding the act of sipuk, see the Rambam on the Mishnah in Orlah 1:5.

[xii] Z. Amar, Crops in the Land of Israel during the Middle Ages, Jerusalem 5760, p. 245 (Heb.); A.M. Watson, Agricultural Innovation in the Early Islamic World, London-New York, 1983, pp. 45–48.

[xiii] Ibn Waḥshiyyah, Al-Filaḥah al-Nabaṭiyah (Nabataean Agriculture) (his work is mentioned by Rambam and Rabbi Yehuda HaLevy), Tawfīq Fahd (ed.), Damascus 1993–1995, pp.13, 1289 (Arabic).

[xiv] Ibid., p. 177.

[xv] See, for instance, the Andalusian book on husbandry, written by an anonymous author circa 10–11th century. This text also mentions grafting an etrog and orange, as well as an etrog with a common jujube or pear: Andalusi Anonimo, Kitab fi Tartib Awqat al-Girasa wa-I-Magrusal (<<Un tratado agrícola andalusí anónimo>>, An anonymous agricultural treatise), Ángel C. López (ed.), Madrid, 1990, pp. 74–75 (Span.). See also the work by Abd al-'Ani al-Nablusi, 17–18th Century, Kitab al-em al-malaha fi 'al-em al-falaha (The husbandry profession), Beirut, 1979, pp. 77–78 (Arabic).

[xvi] Rambam, Hilchot Kila'im 1:5: "For example, the one who grafts a tree on another tree, for instance, an apple on an etrog or an etrog on an apple, behold this one receives "Torah lashes" [for transgressing a Torah law] in any place, whether in the land or outside of the land. And the same applies to one who grafts a vegetable on a tree, or a tree on a vegetable, this one is lashed in any place. " The Rambam specifically cites an example of an impossible graft, which cannot persist. It could be that this is because he believed that the rationale for the prohibition is not necessarily due to the concern that they will produce new grafted offspring, but due to the prohibition against unnatural intercourse (Guide for the Perplexed III, chap. 49, Kapach ed., pp. 396–398) and to distance ourselves from idolatrous customs and the immoral practices accompanying them. Rambam writes that grafting two different species of trees is prohibited, since "we must keep away from the opinions of idolaters and the abominations of their unnatural sexual intercourse "; even any act that is unrelated to idolatry is prohibited if it negates common sense (ibid., part III, chap. 37, pp. 361).

[xvii] Abd al-latif al-Baghdadi, Kitab al-ifadah wa'l-i'tibar, (The Eastern Key). London, 1965, pp. 66.

[xviii] See, for instance, Responsa Alshich, §110; Responsa Rema, §126.

[xix] This premise is discussed at length by Rabbi Mordechai Yafe, Levush Malchut, OC §649:4. For other rationale on why grafted etrogim are invalid, see Rabbi Avraham Yitzchak HaCohen Kook, Eitz Hadar HaShalem, Rabbi Y. Zoldan ed., Jerusalem 5746, pp. 11–14. For differing opinions on the etrog and lemon and whether they are considered kila'im when grafted together, see Rabbi A. Y. H. Kook, Chukot Ha'aretz, Torah VeHa'aretz Institute, Ashkelon 5766, p. 173, nn. 42–44. Rabbi Kook followed the Rambam's view (Hilchot Kila'im 3:6) that the etrog and lemon are not considered different species (as opposed to Ra'avad; see Eitz Hadar Hashalem, §28. p 137). In my humble opinion, this conclusion may depend on the etrog variety. That is, if it is a Yemenite etrog, then there is a considerable difference in the fruit shape and taste, while the trees are only similar in leave shape. According to the criteria cited by Rambam, then this would mean that the Yemenite etrog and lemon would be considered different species and thus prohibited due to kila'im.

[xx] Rambam, Hilchot Kila'im 1:7.

[xxi]. Note the Chazon Ish's stringency, who ruled that "the offspring of a grafted tree is invalid for the arbat haminim." He maintains that if a shoot or seeds from a grafted etrog tree are planted and a new etrog tree grows from it, all of its fruit will be invalid for the arba minim. The vast majority of poskim disagree.

[xxii] For a comprehensive discussion of the matter, see Rabbi Yaakov Epstein, Chevel Nachalato II, Atzmona, §40, and note by Rabbi Yaakov Ariel, ibid., p. 150; responsa by Rabbi Yoel Friedemann, Emunat Itecha, 67 (Elul 5766 –Tishrei 5767), pp. 72–73.

[xxiii] For this reason, there are those who do not rely on these characteristics, rather on tradition only, similar to the laws of kosher fowl. See Chatam Sofer, OC, §207; Mishnah Berurah OC, §648:65; Rabbi A.Y.H. Kook maintained that it is even difficult to rely on a chazakah and tradition—only on strict supervision of etrog cultivation in the Land of Israel. See Eitz Hadar Hashelem (ibid.), pp. 15–16, and §54, pp. 256–257.  

[xxiv] This can explain why it is permissible to mix tree seeds together: this process can also take place naturally. In contrast, the prohibition of kilei ilan refers to an artificial, human act "kilei ilan refers only to grafting" (Rambam, Hilchot Kila'im 1:6).

[xxv] E. Goldschmidt, "Comparative genetic study of 12 etrog strains," Halichot Sadeh, 146 (5765), pp. 21–31 (Heb.). We are not completely ruling out the possibility of natural hybridization of the etrog with other types of citruses, whose genetic influence manifests also in the seeds and not only in the fruit itself. Even if it is true that only from a tree sprouted from such seedlings (as opposed to fruit produced from an etrog tree shoot) can there be fruits that display characteristics of other citrus fruits. In recent generations, the etrog tree is propagated vegetatively through shoots, so the fruits are not a result of natural hybridization. It is for this reason, it is impossible for any other tree to pollinate it. However, it turns out that there were extended periods where seedlings were chiefly used for etrog propagation, which is the way Jews were able to bring etrogim with them to all over the Diaspora (see Goldschmidt, ibid., pp. 25, 29–30). The bottom line is, though, while theoretically such pollination is possible, in practice the concern of hybridization between etrogim and other citruses is not supported by the genetic studies on the matter.

[xxvi] In contrast, it is possible that artificial, initiated sexual propagation between two different species would be prohibited just like grafting two different species of trees. This is the opinion of Rabbi Shmuel HaLevy Wozner, Responsa Shevet HaLevy IX, §224. Rabbi Shaul Yisraeli, though, was lenient in his response to Rabbi Yoel Friedemann: HaTorah VeHa'aretz III, Kfar Darom 5777, p. 121. It seems that this is the main consensus among the poskim: since kilei ilan is derived from cross-breeding, the prohibition relates only to a physical bond with the tree, similar to the intercourse that takes place when there is a physical contact between the bodies of two different animals. See also Rabbi Y. Epstein, Chevel Nachalato II, p. 148.

[xxvii] Rabbi Yigal Ariel, "Anaf etiz avot," Techumin, 11 (5750), pp. 180–181.

[xxviii] M. E. Wiechselfish, "What is an arava and what is a tzafafa," Teva Va'eretz, 11 (5730), pp. 285–290 (Heb.); "A kosher aravah, an invalid aravah, and tzafafa," Hama'ayan 11 (5731), pp. 37–49 (Heb.); Y. Feliks, Flora and Fauna in the Bible, Jerusalem 5744, pp. 159–163 (Heb.); Rabbi Y.H. Amichay, "What is the aravah," Emunat Itecha, 12 (5776–7), pp. 12–15, especially n. 3. In contrast, see Rabbi Tzvi Pesach Frank, Har Tzvi, YD, Jerusalem 5724, §181; Rabbi Y. Zoldan, "The aravah is not a eucalyptus (response)," Emunat Itecha, 13 (5757), pp. 27–30 (Heb.).

[xxix] Extensive literature has been written on the subject. See the summary of the topic by Prof. Yehuda Feliks, Flora and Fauna in the Torah, p. 149–156 (can be found online in Otzar HaTorah, Chay vatzomeach ba-torah, see the first 40 pages); A. Weisfisch, The Canary Palm: on its kashrut for Sukkot, Jerusalem 5778 (Hebrew).

[xxx] See Vayikra Raba 30:12: "Just as this willow lacks taste and smell, so too are the People of Israel: they include people who have neither Torah or good deeds. And what does the Holy One Blessed Be He do to them? It is impossible to destroy them; rather, says the Holy One Blessed Be He: 'They should all be bundled together in one bunch, and those [the other types of Jews] should atone for those. And if you did so, at that moment I am exalted.'"