Foeniculum vulgare Miller: Cell Culture, Regeneration, and the Production of Anethole

Abstract

Fennel (Foeniculum vulgare Miller) belongs to the Umbelliferae family and was originally found around the Mediterranean Basin. It has long been cultivated and introduced into many regions outside of that zone and has become naturalized in some of them. Although it can bear widely different climates and be cultivated in cold climates as well as in tropical regions, it develops best in temperate climates. In the Mediterranean climate, wild fennel often grows densely, with a potentiality of invading crops. In some areas where it has become naturalized, as in California for example, it has spread so much that in some cases it has become a weed (Bailey 1930). As in most UmbeUiferae, the plant has secretory canals in all the organs (Kadry et al. 1978) and produces an essential oil rich in aromatic components. The chief constituent of the essence is anethole (Fig. 1), which gives the plant its anise fragrance, but it also contains, in variable quantities, other elements, such as fenchone, estragole, anisaldehyde and terpenes (d-pinene, α-d-phellandrene, camphene) (Vlahov et al. 1964; Fujita et al. 1980). The genus Foeniculum is monospecific, and is represented only by the vulgare species. The latter, however, has been split into two subspecies: ssp. piperitum (Ucria) Coutinho and ssp. capillaceum (Gilib.) Holmboe (Hegi 1966). Foeniculum vulgare ssp. piperitum is a perennial type of fennel that only grows wild and can be differentiated from ssp. capillaceum by its short and rigid lobed leaves, as well as by a small number of rays in the umbels and by its very bitter fruit. The ssp. capillaceum, on the contrary, is characterized by long and supple lobed leaves as well as by a large number of rays in the umbels and less bitter fruit. In the latter subspecies, three varieties are usually distinguished. The variety vulgare (Miller) Thellung (Foeniculum vulgare Miller) (bitter fennel) comprises a group of perennial plants with rather long fruit having a more or less bitter taste. The variety dulce (Miller) Thellung (=Foeniculum dulce Miller = Foeniculum panmorium DC.) (sweet fennel), on the contrary, consists of annuals, exceptionally biannuals, with smaller fruit, whose sweet taste is a result of the low fenchone content in the essential oil (Osisiogu 1967; Betts 1968). The variety azoricum (Miller) Thellung (=Foeniculum azoricum Miller) (Italian fennel, Florence fennel), probably stemming from one of the above varieties by horticultural selection, also consists of annuals producing small sweet fruit. In these plants, however, young leaves of the rosette have hypertrophied and thick sheaves that form a “bulb” similar to that of celery.