Influence of Co-distillation with Weed Biomass on Yield and Chemical Composition of Rose-Scented Geranium (Pelargonium Species) Oil

Abstract

A laboratory experiment was performed to study the influence of distilling rose-scented geranium (Pelargonium species) biomass together with different proportions (0, 5, 10, 15 and 30% by weight of rose-scented geranium biomass) of biomass of weed species growing in rose-scented geranium fields, on the yields % and compositions of oils of cultivars Algerian, Bourbon and Kelkar. Crop:weed mixtures reduced oil yields of all the three cultivars in comparison to control (pure crop biomass). Combined distillation of biomass of cv. Algerian with weed biomass decreased the concentrations of linalool, geraniol, geranyl formate, 10-epi-γ-eudesmol and increased the contents of isomenthone, citronellol and citronellyl formate in its oil. This distillation method resulted in enhancements in isomenthone, citronellol and reductions in geraniol and geranyl formate in the oil of cv. Bourbon. In cv. Kelkar, the percentages of linalool and isomenthone increased, but that of citronellol and geraniol decreased in crop:weed mixed distillations.

Key Word Index

Pelargonium sp., Geraniaceae, rose-scented geranium, weed biomass co-distillation, cultivars, oil yield, essential oil composition, citronellol, geraniol.

Introduction

Weeds compete with crop plants for light, water and nutrients. In our investigations, we observed changes in yields and chemical profiles of oils of citronella (Cymbopogon winterianus Jowitt.) cv. Java 2 and rose-scented geranium (Pelargonium species) cv. Bourbon when these crops were grown in association with weeds (1,2). Different species of weeds grow in rose-scented geranium fields. Some of the grass species and small weeds with prostrate habit grow in close proximity to the base of rosescented geranium plants; often their branches and leaves get intermingled with branches of the crop. Such weed species, if not weeded may get mixed with rose-scented geranium at the time of harvest and get distilled along with the crop biomass. Though, the weed biomass may constitute a small percentage of the crop biomass, information on the influence of admixture of weed biomass with crop biomass at the time of distillation on the composition of essential oil of rose-scented geranium is lacking. Therefore, in this laboratory study, the effect of combined distillation of rose-scented geranium biomass with biomass of weed species growing in rose-scented geranium fields, on yields and chemical compositions of oils of three cultivars of rose-scented geranium was investigated.

Experimental

Rose-scented geranium is cultivated as a multi-harvest, perennial crop in the semi-arid tropics of south India. Three cultivars namely, Algerian, Bourbon and Kelkar are grown. The oil of Algerian is rich in citronellol, that of Bourbon is rich in citronellol and geranioi and the oil of Kelkar is rich in geraniol (3). A number of weeds infest the rose-scented geranium field during its crop growth period. The weed species identified with the crop are: Aerva lanata (L.) Juss.; Boerhaavia diffusa L.; Chloris barbata S.W.; Cleome viscosa L.; Cynodon dactylon (L.) Pers; Cyperus rotundus L.; Catharanthusroseus (L.) G.Don.; Euphorbia hirta L.; Evolvulus alsinoides L; Pathenium histerophorus (L.) Poit; Phyllanthus amarus Schum. et Thonn.; Tephrosia purpurea L.; Trihulus terrestris L. and Tridax procumbens L. (2).

The experiment was carried out at Central Institute of Medicinal and Aromatic Plants, Field Station, Hyderabad, India. The experimental location experiences semi-aridtropical climate. Rose-scented geranium cvs. Algerian, Bourbon and Kelkar were grown following standard agricultural practices (4). Two sets of experimental plots were maintained for all the cultivars. In one set the cultivars were manually weeded and the crops were maintained weed free. In the other set, weeds were allowed to grow along with crop plants. Fully grown rose-scented geranium plants were harvested from weed free plots. At harvest, the shoot biomass of the three cultivars of rose-scented geranium and the above-mentioned weed species (from weedy plots of the three cultivars) were cut separately. Specific proportions (5, 10, 15 and 30 percent by weight of rose-scented geranium green biomass) of biomass of the weed species was mixed with rose-scented geranium biomass (500 g) of the three cultivars. A control (pure rose-scented geranium biomass) treatment was maintained for each of the cultivars, for comparison. All the treatment (three cultivars × five treatments) samples were hydrodistilled in duplicate in modified Clevenger-type apparatus for 3 h for isolation of essential oils. Pure weed biomass was also distilled for isolation of any oil from the weed species. oil yields (oil contents, %) were recorded and the oil samples were analyzed for their chemical composition.

GC analyses were carried out using Perkin Elmer gas chromatograph (model 8500) equipped with flame ioiiization detector (FID), GP-100 printer-plotter and an electronic integrator, employing a bonded phase fused silica capillary column BP-1 (25 in χ 0.5 mm, film thickness 0.25 µm) coated with polydimethylsiloxane. Nitrogen at 40 mL/min flow rate (linearvelocity 34 cm/s) and 10 psi inlet pressure was used as the carrier gas. Temperature programming was from 60°-220°C at 5°C/min ramp rate with a final hold time of 10 min. Injector and detector were maintained at 250°C and 300°C, respectively. The oil samples (0.1-0.2 µL) were injected neat with 1:80 split ratio.