Monarda fistulosa L., native to the Canadian prairies, is drought tolerant, winter hardy, and may yield an essential oil high in geraniol content (Marshall and Scora 1972; Mazza et al. 1987). When this native species is crossed with M. didyma, vigorous hybrids, yielding essential oils rich in geraniol, linalool, thymol, carvacrol, 1,8-cineole, and other terpenes can be produced. In the present study, the content and composition of the nitrogen extracted volatiles and hydrodistillated oils from eight winter-hardy, powdery mildew, and rust-resistant hybrids were determined, with the aim of developing new alternative crops for Canadian agriculture.
The essential oil was extracted by hydrodistillation of the plant material using 600 g in a 5 liter round-bottomed flask with distilled, deionized water (2,400 ml), and a receiver for oils lighter than water. The distillation period was 2 h, and the essential oil content was determined on an oil weight to dry tissue weight basis. Headspace volatiles of the chopped plant material were extracted and concentrated by passing a stream of purified nitrogen (80 ml/min for 15 h; 21±1°C) over the samples. The volatiles were adsorbed onto Tenax GC traps prepared by packing 100±2 mg of 60-80 mesh Tenax GC into a 65 mm i.d. x 12 cm Pyrex tubing between pesticide grade silanized glass wool plugs. Monarda volatiles were subsequently eluted from the Tenax GC traps with 1 ml of freshly redistilled diethyl ether. Essential oil and headspace samples were analyzed using a Varian Model 3400 gas chromatograph equipped with a flame ionization detector (FID). A 30 m x 0.25 mm i.d. fused silica capillary column packed with 1 µm J&W DB-5 [polymethyl(5% phenyl) siloxane] was used for the separation of volatiles. The operating conditions were: injection port temperature, 230°C; detector temperature 250°C; column temperature programmed at 60°C for 0 min, 60deg. to 104°C at 4°C/min, 104° to 182°C at 6°C/min and at 182°C for 6 min; carrier gas flow rate, 1 ml He/min; linear velocity 24 cm/s.
Identification of the compounds was made by combined gas chromatography mass spectrometry (GC/MS) and by comparing retention times of monarda components with those of authentic compounds. A Finnigan MAT 90 mass spectrometer coupled with a Varian Model 3400 gas chromatograph was used for GC/MS analyses.
Linalool represented 45.7% of selection 80-1A, 49.8% of `Marshall's Delight', and 67.0% of selection L87-1 essential oil (Table 1). This substantiates the close relationship existing between these three selections (Fig. 2); however, the other closely related selection, 80-1B, had only 0.4% of linalool, and a high amount of carvacrol (22.3%), 1,8-cineole (22.2%), ß-pinene (13.8%), and ocimene (6.2%). Therefore, a definite genetic segregation appears to have occured.
The oxygenated terpene, 1,8-cineole, occurred in all samples and represented 4.8, 14.1, and 22.2% of the oils from 'Marshall's Delight', '75-1B', and '80-1B' Monarda, respectively. 1,8-Cineole, also known as eucalyptol, cajuputoal, 1,8-oxido-p-menthane, or 1,8-epoxy-p-menthane, occurs in numerous essential oils (about 270) and is used widely in pharmaceutical preparations and food products such as beverages, ice cream, candies, baked goods, and chewing gum.
Propagation of these selections of monarda can easily be achieved through crown divisions, but this method is cumbersome and inefficient. A more effective and rapid method of propagation has been found to be through plant cuttings of actively growing stems. Stem cuttings, approximately 10 to 12 cm in length, are taken and all but two leaves removed, including the shoot tip. The bases of the cuttings are dipped in 1,000 ppm IBA rooting compound and placed in sand in a misting chamber. Cuttings taken in early June when the plants are actively growing produce root initials within one week and are ready for transplanting within 14 to 16 days. Propagation by tissue culture has also been successfully carried out in our laboratory using leaf cuttings.
Weeds do not pose a problem in the production of monarda. Herbicides such as trifluralin, terbacil, solan, and paraquat used together with good cultural practices can maintain a weed-free plantation. Trifluralin (1.12 kg/ha) should be used pre-plant incorporated when monarda is established. In the second year and every year thereafter, paraquat can be applied before the monarda shoots reach a height of 5 cm, to kill the early spring weeds. Application of herbicides in a commercial field, however, should only be used if the chemicals are legally registered for such use on this crop. This also kills off the monarda shoots. Application of terbacil (1.68 kg/ha) and 1 to 2 cm of irrigation should follow.
Rust, Puccinia mentha, is the major disease of Monarda. It has caused defoliation, girdling of stems, and degeneration of plants. The disease is spread by aerial rust spores under cool, cloudy, moist weather conditions. Relatively good control has been achieved by applying a contact herbicide, paraquat, in early spring when the monarda shoots are only about 5 cm tall to destroy all vegetation and thereby remove the required host for the spores.
Essential oil yield varies from about 0.65 to 1.2 g/100 g of fresh plant material (Table 1), or depending on the hybrid, 60 to 125 kg of oil/ha. As a result, it is our believe that four of these hybrids of monarda may have the potential of becoming commercial sources of geraniol, linalool, tymol, and carvacrol.
|Relative composition (% of total oil)|
|Peaky||Constituent||Morden #3||Marshalls Delight||75-1A||75-1B||84-2||80-1B||80-1A||L87-1|
|Yield of oil (g/100 f.wt.)||1.2||0.6||1.1||0.6||1.1||0.7||0.8||1.0|
(% of total essential oil)
|Peaky||Essential oil constituent||Oil||Headspace|