Characterization and Yield Evaluation of Essential Oils from Different Tagetes Species(a)

Journal of Essential Oil Research: JEOR, Sep/Oct 2004 by Marotti, Mauro, Piccaglia, Roberta, Biavati, Bruno, Marotti, Ilaria

Abstract

Six species of Tagetes (T. erecta, T. filifolia, T. lucida, T. minuta, T. patula and T. tenuifolia), grown in northern Italy, were evaluated for their morpho-phenological characteristics, biomass yield and essential oil composition. The species showed marked differences in plant height, shape, flower size, habit and vegetative cycle length as found for T. filifolia which finished the vegetative cycle without reaching the flowering stage. The leaves always showed fresh material yields many fold higher than flowers (on average 26.8 and 4.4 t ha,^sup -1^ respectively). Tagetes erecta and T. patula produced significantly higher amounts of flowers than the other species (7.3 and 6.4 t ha,^sup -1^ respectively), whereas Tagetes lucida and T. filifolia were those with the highest yields of leaves (41.9 and 33.31 ha,^sup -1^ respectively). The oils isolated by steam distillation from the flowers and leaves, were analyzed by GC and GC/MS. The flowers and the leaves of each species showed very similar qualitative oil compositions and the leaves, on average, were richer in oil contents. The oil yields between the flowers and leaves showed differences highly significant (on average 1.8 and 150.3 kg ha,^sup -1^ respectively). Tagetes erecta, T. minuta, T. patula and T. tenuifolia comprised the same pool of components (dihydrotagetone, tagetones, ocimenones and piperitone) which showed different and typical ratios in each species and, piperitone, (E)-tagetone, terpinolene and (E)-ocimenone were those more abundant respectively. Tagetes filifolia and T. lucida had methyl chavicol as the main compound.

Key Word Index

Tagetes erecta, Tagetes filifolia, Tagetes lucida, Tagetes minuta, Tagetes patula, Tagetes tenuifolia, Asteraceae, morpho-phenological characteristics, essential oil composition, limonene, (Z)-[beta]-ocimene, (E)-[beta]-ocimene, dihydrotagetone, terpinolene, (E)-tagetone, methyl chavicol, (E)-ocimenone, piperitone, [beta]-caryophyllene.

Introduction

Tagetes (marigold) is an important genus belonging to the Asteraceae family, native to Mexico and Central America, brought from the New World to Europe in the 16th century and, at present, worldwide spread. Some species such as T. erecta, T. patula and T. tenuifolia are cultivated as ornamental plants, while T. minuta can also be found as wild species and, in some countries i.e. Australia and South Africa, it has become a noxious plant (1). Marigold, in the native areas is also traditionally exploited for human use as beverage (2), as condiment and in folk medicine (3). In the last years, characterized by an increasing attention toward medicinal plants for the maintenance of personal health and well-being, this genus has been the subject of renewed interest in most developed countries, as a source of numerous multifunctional secondary metabolites which found application as natural substances instead of chemical synthetic compounds. Marigolds are rich in carotenoids, used as food colorants and feed additives (4), that also are reported to possess anticancer and antiageing properties (5). Other constituents such as flavonoids are reported to have pharmacological properties (6), while thiophenes possess marked biocidal activity (7,8). Finally, essential oils are known for their antibacterial and insecticidal properties (9,10). In particular, some typical constituents of Tagetes ssp. oils are reported to have specific properties i.e. ocimenones show antifungal and larvicidal activity (11,12) and dihydrotagetone, tagetones and piperitone possess a strong inhibition activity against the growth of Grampostive and Gram-negative bacteria (13). Moreover, ocimenones, dihydrotagetone, tagetones, ocimenes along with methyl chavicol possess a pleasant scent and are currently employed in flavor and fragrance industries (14). Methyl chavicol which is mainly used in food products since 1965 when it was recognised as safe (15) and then approved by FDA, more recently, has been object of discussion considering the evidence of its carcinogenicity in experimental animals. Due the need of long-term studies to better assess the implications of this compound for human health, a limit of 0.05 mg/kg is recommended by the CEFS (16).

The oil composition shows a great variability in the Tagetes genus (1,17) and this chemical diversity, which is genetically determined and strictly related to the species, can represent a valuable contribution for the correct chemotaxonomic identification of the plants (18). It is also well known that several factors such as crop growing location, plant development stage, different parts of plant used for oil isolation (19, 20), soil composition (21) and mineral fertilization (22) can influence the oil content and the quantitative ratios of the oil components within the same species. The oil composition along with the agronomic characteristics, are parameters of great importance to determine the quality and the uses of medicinal and aromatic plants (23).

In our work, the agronomic yields and the oil compositions of some Tagetes ssp. grown in northern Italy, were evaluated for the possible exploitation of this genus as alternative crop of economical interest in some marginal areas considering also that the current European Agricultural Policy encourages the cultivation of no-food crops for industry.