The search for the authentic citron (Citrus medica L.): historic and genetic analysis

The citron (Citrus medica L.) was the first citrus fruit known to the Europeans and was probably, for many years, the only one known. The citron has been and is still used for the Jewish ritual of the feast of Tabernacles. Citrons have been grown for many generations all around the Mediterranean. Grafting of the citron on other citrus rootstocks became common during the 16th century. Following the ancient popular belief that grafting results in some kind of hybridization (see Greene, 1983), citron fruit from grafted trees were declared by Jewish authorities as unfit for the ritual of Tabernacles. This initiated a search for citrons growing in areas outside the Mediterranean, which supposedly were never grafted; Morocco and Yemen are among these remote areas. In view of the marked diversity in geographical origin and fruit characteristics, one may wonder whether the different citron types are genetically close to one another. Moreover, the Yemenite type resembles in its external appearance some Indian citrus fruits. Could the Yemenite citron have arrived from India via the sea and actually belong to a different citrus species? These doubts prompted us to undertake a comparison between 12 different citron types, including types from Israel, Italy, Morocco and Yemen, using modern molecular techniques. The results obtained are very clear and, perhaps somewhat surprising. Notwithstanding diverse geographical origin and considerable morphological variation, especially in fruit size and shape, presence of pulp, and persistence of style, all the citron types examined revealed a high degree of similarity. Within the polymorphisms obtained, types from the same geographical origin (Yemen, Morocco) showed the highest similarity. There was no sign of introgression by lemon or other citrus genomes into any of the citrons examined. It is particularly noteworthy that the Yemenite citron did not differ from the rest, thereby confirming its assignment to Citrus medica and rendering the direct India-Yemen link unlikely. Thus, the Yemenite citron as well as the Morocco citron have most probably originated in the Mediterranean. The results of the present study highlight the prominent role played by the Jews in the spread of the citron in the course of their wandering. In conclusion, all the currently acknowledged types of citron appear to be “true”, authentic citrons.