History of Citron (Citrus medica L.): Biological and Cultural Features

The citron (Citrus medica L.) is assumed to be one of the three forefathers of the Citrus genus and the first to have reached the Near East. For many generations citron fruits, praised for their beauty and medicinal properties, have been the major citrus fruit known in Europe, as indicated by the large portion of Ferrari and Volkamer classical texts devoted to citrons. Its adoption by the Jews for the sacred Tabernacles worship turned the citron(=Etrog) fruit into a Jewish symbol, subject to intense legal and customary discourse. Jews apparently played a central role in the distribution of citrons within the Mediterranean and beyond. Thus, the history of the citron has in addition to its bio-evolutionary course, a unique human dimension; both aspects acted in close interaction and are reflected in the current state of citron horticulture and trade. The ancient history of the citron in its South-East Asia center of origin is still shrouded in mystery, but its contribution to the genetic makeup of the lemon tribe and other cultivars is beyond doubt. Interestingly, although citrons are mono-embryonic and mainly propagated by seed, the vast majority of emerging seedlings  show close similarity to the mother plants, with hybrids only seldom encountered. This indicates, along with ecological evidence, that citrons maintain a self-fertilization mechanism, which preserves their species identity. Citron may however serve as the male parent; e.g., the Bergamot, which has been shown to be a citron-sour orange hybrid and, like the citron, has a persistent, non-abscising style. A central theme in the use of citron-Etrog for Tabernacles is the grafting problem. Citron trees are very degenerate, sensitive to Phytophthora root collar rot and, to a lesser degree, exocortis. Grafting has been used extensively to overcome these problems, at least since the 16^th century. However, the use of ‘grafted’ citrons for Tabernacles was controversial, according to religious authorities, and rejected by most religious communities. This prompted a search for non-grafted or allegedly never-grafted citrons in remote places such as Yemen and Morocco. As a matter of fact, according to current scientific views, grafting is not expected to involve genetic changes in the scion, and there seems to be no scientific basis for the rejection of grafted citrons. Furthermore, a genetic comparison between Mediterranean, Yemenite and Morocco citrons showed them to be closely similar and distinctly different from lemon and other citrus species.