The genus Carum Rup. ex Linn. Syst. ed I. (1735) from the family Umbelliferae (= Apiaceae) comprises 195 species. In Europe five species grow: Carum carvi L., C. heldreichii Boiss., C. multiflorum (Sibth. et Sm.) Boiss., C. rigidulum (Viv.) Koch, ex DC, and C. verticillatum (L.) Koch. From the economical point of view, the most important is caraway, Carum carvi L. Sp. PL, 263 (1753), known also as Carum aromaticum Salisb., C. decussatum Gilib., C. officinale S.F. Gray, and C. careum Bub. (Index Kewensis 1895-1974).
Caraway is biennial herb which grows up to 150 cm, indigenous to Europe and Asia, and widely cultivated in many countries for its aromatic fruits. Leaves are two-to three-pinnate, lobes 3 to 25 mm linear-lanceloate or linear. The lowest leaf segments are at least twice as long as wide. Petals whitish or pink. Fruits 3 to 6 mm, ovoid, 3 to 3.5 times as long as wide, with low rounded ridges, smelling strongly after crushing, 2n = 20.
Carum carvi L., caraway, is known as a spice and a medicinal herb. Fruits of this plant are used as flavoring spice in various foods. Dried fruits are used for preparing a stimulating tea, they are also a mild stomachic.
Caraway fruits contain essential oil (localized in vittae) from 3 to 7%, 20% of fixed oil (i.e., nonvolatile oil) and proteins. The main component of the essential oil is the ketone carvone from 50 to 60%, the terpene d-limonene from 40 to 50%, and small amounts of other constituents, including carveol and dihydrocarvone. Salveson and Baerheim Svendsen (1976), using gas liquid chromatography, presented the detailed composition of caraway oil. Embong et al. (1977) described the 12 main constituents of the essential oil obtained from plants growing in Canada. Dijkstra and Speckmann (1980) studied autotetraploids of caraway. In these plants the yield of essential oil in fruits was 35.6% higher when compared to diploid plants.
Caraway oil possesses carminative properties, is often used to correct nausea and griping. Lewis (1977), discussing the problem of allergy, mentioned carvone as a sensitizing substance and for this reason classified Carum carvi among the plants causing contact dermatitis. Because of this allergic potential essential oil cannot be used as a flavor for toothpaste.
Weiss (1982) classified the fruits of Carum carvi, together with fruits of Foen-iculum vulgare and Anethum graveolens, as the most important plant raw stuffs with carminative properties. Lutomski et al. (1987) mentioned Fructus Carvi as one of the components of four prescriptions for making plant mixtures. Three of these compositions are used as Remedia Carminativa, one as Remedium Digestivum. Oleum Carvi is also a component of a drug used as Remedium Corminativum.
Caraway has great nutritional requirements and therefore the cultivation of this plant is not easy. There are many factors, which influence the dynamics of growth and the crop of caraway. Formanowicz (1969) observed that a significant dependence of the germination capability on moisture content is found in caraway seeds. Bochefiska and Kozlowski (1969) studied the fluctuations in essential oil, water content, and germination capability of C. carvi L. fruits, during ripening and storing. These authors found that seeds of high germination capability, above 80%, and of high essential oil content, within 5 to 7%, can be obtained only when the weather during the ripening season is warm (daily temperature about 18 °C), with not more than 400 mm of rainfall. Okoniewska (1977) tested various mutagenic agents for application in caraway. As a result of this work, two mutants were selected, scrub line 211, after irradiation by fast neutrons, and line 298, with large fruits obtained by chemical mutagen treatment. Kordana et al. (1983) found that the increase of mineral fertilization level accelerates the rate of the plant mass production, enhances the mass of fruits but does not affect the content of essential oil. Caraway has a high demand for nitrogen and potassium but lower for calcium and phosphorus. Weglarz (1983) studied the effect of fertilization, soil moisture, time of sowing, and amount of seeds per ha on the development and cropping of caraway. It was found that these factors significantly influenced the number of leaves, root mass, the number of flowering plants, and the crop itself. A favorable growth, development, and crop of caraway were observed in the case of an early sowing in the spring, a low amount of sowing seeds (5 kg/ha), and a high level of mineral fertilization.
Apart from agricultural factors which affect cropping of Carum carvi, the second problem which also must be taken into account is that caraway is often attacked by a large number of diseases, that cause a decrease in fruit yield. Heavy losses are caused by bacteria, fungi, and insects, which can damage all parts of the plant. Roots are infected by various species of bacteria: Fusarium, Erwinia, Pseudomonas, and also by the insect, Psila rosae. Diseases of the stems are caused by bacteria (Erwinia, Pseudomonas, Xantomonas), fungi (Centrospora acerina, Phoma anethi), and insects: Aceria carvi, which deforms leaves and umbels; Lygus campestris, Lygus calami, Lygus lucorum attaceka, the young stems, leaves, and umbels; species of Cavariella and Aphis subdue, the higher part of stems; Lasioptera carophila damages the umbels. Depressaria nervosa feeds on flowers and fruits of caraway.
Aromatic Compounds in In Vitro Cultures
The production of essential oil and its components in tissue culture is still not satisfactory. Plant tissue culture in many cases lost the ability to synthesize the components of essential oils typical for intact plants. Th is may be caused by lowering the level of cell differentiation necessary for the formation of secretory structures. Kuzovkina et al. (1975), discussing the problem of essential oils in the culture of isolated plant tissues, paid attention to the close connection between the bio-synthetic property of the tissues cultured and their morphology. For the study of the biogenesis of essential oils in tissue culture, it is very important to know the physiological dependences and primary and secondary metabolism in intact plant and in tissue culture. Staba (1980) mentioned only four species in which the production of essential oils in tissue culture has been studied, and none of them belonged to the Umbelliferae (= Apiaceae) family. Among the many plants which contain essential oil, most studies are on members of the Labiatae, in which the biosynthesis of the components of essential oil in tissue culture was observed. Fewer studies concern the plants of the umbellifers. Sardesai and Tipnis (1969) found geraniol in tissue culture of Coriandrum sativum. Becker (1970) studied the formation of volatile substances in plant tissue cultures of: Pimpinella anisum, Foeniculum vulgare subsp. capillaceum var. azoricum, and Levisticum officinale. The steam distillates of Pimpinella anisum roots and leaves differentiated in tissue culture showed a substance which was already known from the entire plant, but not in the same quantitative proportion. Becker (1970) also discussed the dependence of the accumulation of volatile compounds on the degree of differentiation. Collin and Watts (1986) found that suspension culture of celery (Apium graveolens) produced phthalides (flavor compounds) and limonene (terpenoid — a component of essential oil) during the exponential phase. The cultures lost the ability to synthesize the flavor compounds after a prolonged period of subculture.
Mulder-Krieger et al. (1988) presented a review on the production of essential oils and flavors in plant cell and tissue cultures. In this publication six species from the Umbelliferae (Apiaceae) family were mentioned. The most interesting was the production of the phthalides compounds (components of essential oil) by suspension with embryoids of Apium graveolens. In suspension culture of this species phthalides and monoterpene compounds were also found. Monoterpene compounds were produced by callus of Coriandrum sativum, Daucus carota, Foeniculum vulgare, Levisticum officinale, and Pimpinella anisum.
Conclusions and Prospects
Many of the experiments done on micropropagation of caraway indicated that this method should find practical application. A high rate of micropropagation can be obtained in vitro via somatic embryogenesis. The number of caraway plants produced through somatic embryogenesis was significantly higher as compared to the micropropagation from existing meristem in seedling shoot tip.
It is expected that in vitro techniques will help to solve some of the problems concerning improvements of caraway and its breeding. In future, more attention should be paid to encapsulation of somatic embryos in gel-like substances as synthetic seeds, which could be comparable to dry seeds from the point of view of planting equipment. Micropropagation of medicinal and aromatic plants, from the Umbelliferae (= Apiaceae) family, especially caraway, appears a very promising method.
Selections from the book: “Medicinal and Aromatic Plants III”, 1991.