Distribution and Importance
Lavandula species are of great interest due to their content of essential oils, which are important to the perfume, cosmetic, flavoring and pharmaceutical industries. They also have numerous other applications, including their uses as ornamental and melliferous plants.
The genus Lavandula, of the family Labiatae (Lamiaceae), encompasses about 20 species almost exclusively distributed in the Mediterranean area, where they are characteristic components of the degradated mediterranean shrublands. They usually grow in zones with scanty summer rainfall and exhibit marked xerophytic tendencies. Lavandula plants are evergreen shrubs up to 100 cm (-200 cm). Their stems have a characteristic square shape and the leaves are almost linear to oblong-lanceolate, and usually tomentose. The upper branches bear terminal spikes consisting of ver-ticillasters six- to ten-flowered, with purplish corollas. Most aboveground plant organs are covered in hairs and glands that emit an aromatic fragrance.
Within the genus Lavandula, only three species are considered to be of current economic interest: Lavandula angustifolia Miller (Synonym: L. officinalis Chaix, L. vera CD., L. spica L. nom ambig.), Lavandula latifolia Medicus (synonym: L. spica auct., non L.), and the hybrid lavandin (L. angustifolia X L. latifolia). The distribution and importance of these chalk-growing species are summarized below.
L. angustifolia is native throughout the western Mediterranean areas, growing wild, at altitudes between 600 and 1000 m, on the dry, barren, sunny mountain slopes of southern France or Italy and the northeast of Spain. It is commonly cultivated in many countries, in addition to those in the Mediterranean Basin, England, U.S.S.R., U.S.A., India etc. L. latifolia has a geographical distribution similar to that of L. angustifolia, growing wild at low altitudes (200-1000 m). Usually it is not planted, since it grows naturally and abundantly in Spain, the main producing country of this species. The hybrid lavandin grows wild at medium altitudes, in those regions where the parent plants coexist. This plant is cultivated on a large scale, especially in France, Italy, and England.
The essential oils of Lavandula species are obtained by steam distillation from the fresh flowering spikes. The amount varies according to the variety, season, and method of distillation. The essential oil of L. angustifolia (lavender oil) has a weight per ml of 0.878 to 0.892 g. Genuine continental lavender oil normally contains not less than 35% esters, calculated as linalyl acetate, the chief constituent of this oil. Other constituents include: cineol; amyl alcohol; d-borneol; geraniol; lavadulol; linalool; nerol; acetic, butyric, valeric, and caproic acids (as esters); traces of d-pinene, limonene, and the sesquiterpene caryophyllene; ethyl n-amil ketone; an aldehyde (probably valeric aldehyde); and coumarin. Lavender oil is chiefly used in perfumery, although it also has uses as a carminative and as a coloring or flavoring agent. It is sometimes applied externally as an insect repelent and is occasionally used in ointments and other pharmaceutical preparations to cover disagreeable odors.
The essential oil of L. latifolia (spike lavender oil) has a wt./ml of 0.894 to 0.915 g. It contains a small amount of esters but a high proportion of free alcohols, especially cineol, camphor, linalool, and borneol. Spike oil resembles lavender oil in its properties and is mainly used in perfumery.
The oil from hybrids of L. latifolia and L. angustifolia (lavandin oil) has a wt./ml of about 0.89 g. It shows characteristics of both lavender and spike oils, containing 20 to 28% esters, calculated as linalyl acetate. Lavandin oil is a substitute for lavender oil in perfumery, being more fragrant than spike oil. It is used largely in the soap industry as a source of linalool and linalyl acetate.
Conclusions and Prospects
Clonal propagation of Lavandula by means of tissue culture technology appears feasible. A review of the present literature clearly demonstrates that in vitro regeneration of Lavandula can be easily achieved through organogenesis from a variety of explant sources, including isolated cells. These results suggest potential applications for selection experiments and somaclonal variation studies, specially for fast multiplication and high yield of desired products. Nevertheless, in order to fully exploit the benefits of the tissue culture technology, more work is required to establish the conditions for plant regeneration from Lavandula protoplasts. Also, more and detailed studies on factors controlling micropropagation of Lavandula via somatic embryogenesis must be undertaken. All these in vitro techniques will certainly improve the breeding and productivity of this important aromatic crop in coming years.
The major secondary products reported from in vitro cultures of Lavandula are essential oils, biotin, and blue pigments. One great success has been the induction and selection of high biotin-producing cell strains. Another important achievement was the immobilization of Lavandula cells and the prolonged production of the blue pigment by gel-entrapped cells. In contrast, progress on essential oil production by cultured Lavandula cells is still lacking. Callus and suspension cultures of Lavandula are unable to accumulate monoterpenes, but contain the enzymes responsible for terpenoid anabolism and may biotransform some monoterpenoid aldehydes to their corresponding primary alcohols. Up till now, our knowledge is not sufficient to overcome the absence of monoterpenes in cultured cells of Lavandula. Consequently, more studies are needed to elucidate the suppression mechanism(s) of terpenoid accumulation to raise its productivity in callus or suspension cultures.
Cryopreservation techniques have been used successfully in suspension cultures of Lavandula. The retention of metabolic and plant regeneration potentials of the retrieved cultures suggests the use of this technology for the storage of germplasm from Lavandula plants with high essential oil content.
Selections from the book: “Medicinal and Aromatic Plants III”, 1991.