A Grafted Esrog
“Passul When Missing Even a Tiny Bit”
Hybrid esrogim are a very serious concern, and one must be careful when choosing an esrog to ensure that it is in fact from a pure strain. Today, most boxed esrogim come with a kashrus certificate, asserting that the esrog in the box is not grafted, the field in which the esrog grew has been in use for many generations, and is known to contain no mix of other species.
Grafting Lemon Branches onto Esrog Trees
The esrog tree is known to be weak and to have a short life span. Therefore, an esrog farmer may wish to graft branches from hardier lemon trees onto his esrog trees in order to produce a hybrid that is sturdier and more profitable. Fruits grown from such mixed species are often more beautiful than purebred esrogim. The Poskim question whether mixing lemons and esrogim transgresses the prohibition against planting or benefiting from kilayim. Since lemons and esrogim are so similar, this might not be included in the prohibition against mixing strains (see Shvus Yaakov 1: 36; Chazon Ish, Kilayim 3:7). This article does not focus on whether making such a hybrid is permitted. Rather, the question is whether this hybrid is kosher for use as an esrog on Sukkos. Hybrid esrogim have been discussed by the most prominent Poskim of the last four hundred years. Numerous teshuvos in regard to this matter have been written by the Rema; Maharam Alshich; the Mabit; Rabbi Betzlalel Ashkenazi; and many others their conclusion is that a hybrid esrog is passul – invalid.
A Hybrid Esrog Is Not an Esrog
Several explanations have been offered as to why hybrid esrogim are passul. The most commonly cited reason is that “a hybrid esrog is not an esrog at all.” This means to say, that the Torah referred to a fruit that is purely esrog, not the combination of an esrog and another fruit (Teshuvos Rema, 117; Magen Avraham 648 s.k. 27; Mishna Berura s.k. 65).
Distinctive Traits of an Esrog
A pure esrog has certain traits that distinguish it from a hybrid. The stem of a hybrid esrog juts out from the bottom, whereas a pure esrog’s stem grows from an indentation on the bottom. The skin of a hybrid is smooth, whereas a purebred esrog is bumpy. The inner white flesh of a hybrid is thin like a lemon’s, whereas a pure esrog’s flesh is thicker. (see Mishna Berurah ibid; the Four Minim – Esrog). Nonetheless, the Mishna Berurah cites from the Chasam Sofer that one may only use these signs to deem an esrog to be passul. When choosing an esrog to use for Sukkos, one must choose only an esrog that was grown in an orchard known to be of pure lineage (see Sha’ar HaTziyun, s.k. 74).
With recent technological advances in horticulture, it is now possible to subject a fruit to laboratory tests, and thereby determine its genetic makeup. Is such a test sufficient to deem a certain, unknown breed of esrogim to be pure and kosher? Rabbi Yechiel Michel Stern, a contemporary expert on esrogim, consulted with other experts in the field and came to the conclusion that even pure and kosher esrogim have some genetic traces of lemons. Therefore, genetic testing is useless to definitively determine which esrogim are kosher (Kashrus Arba’as Haminim, p. 181). How is it that pure esrogim, which had never been grafted with lemons, somehow show traces of lemon?
The esrog plant produces its fruit by means of pollination. Bees carry pollen from the stamens to pistils, causing fruit to grow. However, bees might also happen to carry pollen from the stamens of lemon flowers to the pistils of esrog flowers, thus effecting a cross-pollination of the two species. The resulting fruit carries traces of both parents. One might very well ask why this is not passul, just as the result of grafting the two species is passul. Rabbi Shlomo Zalman Auerbach, zt”l, (cited in Kashrus Arba’as Haminim, p. 182) explained that the branch of a lemon tree is capable of producing fruit by itself. Therefore, when it is grafted to an esrog tree, this is considered the joining of two viable species, resulting in a third, hybrid fruit – which is not considered an esrog. However, the pollen of a lemon flower cannot grow into a fruit by itself. It only provides genetic material, allowing the pistil of the esrog to develop into a fruit. Therefore, the result is considered a kosher esrog fruit, with some traces of lemon.
According to this explanation, it would seem that esrog farmers might be allowed to make use of the latest techniques in agricultural biotechnology, in which chromosomes of a certain species are isolated and injected into a different species, giving it traits of the first species. Since this genetic material could not develop into a plant on its own, and is only capable of altering its new host, the resulting tree may very well be a kosher esrog tree with the longevity and durability of a lemon tree. However, the Chazon Ish (Kilayim 2:15) noted that even in such a case, the esrog would only be kosher if it has both the outer and inner appearance of a pure esrog.